Audio signal representation decoding unit and audio signal representation encoding unit

Abstract

an audio signal representation decoding unit (500) for generating an expanded Ambisonic spatial audio signal representation (562) from a compressed Ambisonic spatial audio signal representation (502) representing an audio signal, the compressed Ambisonic spatial audio signal representation (502) comprising at least one transport channel (501) and side information (503), the side information (503) comprising sound field parameters (529, 549, 718), the sound field parameters comprising, for each spatial sector of a plurality of spatial sectors, a directivity parameter (529, 549, 718) providing information regarding a direction of arrival DoA in the spatial sector, and the sound field parameters comprising, for at least one spatial sector, a sector diffuseness parameter (529, 549) providing information regarding a sector diffuseness of the audio signal in the at least one spatial sector; an audio signal representation decoding unit including a plurality of sector decoding paths (521, 541), each configured to decode a directional sector signal (532, 552) of the expanded Ambisonic spatial audio signal representation (562) in each spatial sector by applying a spatial sector directivity parameter (529, 549) and a sector spread parameter (529, 549) to at least one transport channel (501) or a sector signal (528, 548) derived from at least one transport channel; the audio signal representation decoding unit includes a global diffuse signal decoding path (505) configured to derive a global diffuse signal (501) by applying a global diffuseness parameter (507, 507', Ψ) or other information related to the global diffuseness of the audio signal to at least one transport channel (501); the audio signal representation decoding unit includes a global diffuse signal inserter (560) that combines the plurality of decoded directional sector signals (532, 552) and the global diffuse signal (510) to output an expanded Ambisonic spatial audio signal representation (562); An audio signal representation decoding unit (500).

Description

[Technical Field]

[0001] This document refers to an audio signal representation decoding unit, an audio signal representation encoding unit, an apparatus comprising them, a method and a non-transitory storage unit.

[0002] This document details a new architecture for higher-order directional audio coding (HO-DirAC) for transmission from higher-order Ambisonics (HOA) input to output. This document is also directed to sector-based DirAC systems that combine first- and higher-order DoA with diffusion estimation. [Background technology]

[0003] According to the standard conventional Ambisonics audio signal representation, there is a single direction of arrival (DoA) and a single diffuseness for the entire space. However, it is known that there can be multiple DoAs and diffuseness in multiple spatial sectors. Therefore, a different, more accurate sound field parameter model is proposed herein.

[0004] In contrast to commonly used first-order parameter estimators, the additional information available in the higher-order channels of HOA is exploited. Specifically, the sound field can be characterized by two or more dominant directions of arrival (DoAs), which allows the encoder to separate multiple sound sources per critical band.

[0005] At the decoder, these additional DoAs control the synthesis of multiple directional DoA streams that may originate from multiple sound sources.

[0006] Despite the additional information, the proposed technique may implement current coder structures, maintain the robustness of current first-order Ambisonic (FOA) DirAC, and allow seamless switching between both designs for different coding scenarios.

[0007] Essentially, the proposed technique improves upon the previously known HO-DirAC method by leveraging sector-local and global diffusion information. Specifically, the new technique enables more accurate modeling of realistic sound scenes by accurately and robustly reproducing the global diffusion energy ratio of the input signal, resulting in improved perceptual quality during HOA audio coding and spatial enhancement over previous designs.

[0008] This is because the global diffusion path is similar to that of a first-order system, thus maintaining relative robustness and stability. At the same time, by measuring the DoA for each sector of any number of sectors and reconstructing multiple directional components of the sound field, a more accurate spatial image can be obtained.

[0009] Additionally, the integration of multiple DoAs into an existing primary DirAC system is greatly simplified by the present invention.

[0010] Directional audio coding parameterizes the spatial audio scene in terms of perceptually relevant parameters. These parameters include, for each time-frequency tile, the direction of arrival (DoA) Ω of the incident sound field and a sound field diffuseness measure Ψ that indicates the ratio between the directional and diffuse sound field components. Both parameters are extracted from an active intensity vector estimated from first-order Ambisonics (FOA) (see (References)). The active intensity vector i is given by the well-known formula (see (References)): i=pv The direction of i gives the DoA estimate, and the length compared to the acoustic energy gives a measure of diffusion.

[0011] The decoder may recover certain higher-order signal components from the transmitted FOA signal, as detailed in the HO-DirAC Coder patent (reference). According to (reference), the input FOA signal is split into two rendering paths based on the estimated diffuseness Ψ to perform directional (i.e., 1-Ψ) and diffuse (Ψ) rendering. The directional component is assumed to be a plane wave, and therefore the omnidirectional pressure signal x 00 is decoded as an HOA signal in the direction of Ω by a plane wave extension of . The latter is extracted from the transmitted subset signal. The diffusive component results in the FOA signal, scaled by a function that depends on Ψ.

[0012] The HOA signals allow the input sound field to be segmented by multiple spatial weightings, i.e., beamformers, as shown in Figure 3. The HOA inputs therefore allow the formulation of appropriately weighted FOA signals, as shown in Figure 4. These segmented FOA channels, i.e., sound field sectors, therefore allow the simultaneous estimation of multiple Ω and Ψ in a sound field sector (as in HO-DirAC sector processing (reference)).

[0013] The sector parameter is proposed in (References), but not for spatial audio coding and compression, but for speaker-based rendering and spatial sharpening.

[0014] Prior art devices transmit a single DoA and diffuseness (primary estimate Ψ, Ω) or partially recover these estimates at the decoder.

[0015] Current conventional sound field models assume a mixture of a single directional sound source and a diffuse sound field per time-frequency tile. However, this conventional model is often violated in practice, for example, by multiple directional sound sources within the same time-frequency tile or by specular reflections. Multi-DoA models, such as the proposed sector model, can resolve such scenarios with multiple directional sound sources, thus improving the perceived audio quality.

[0016] Furthermore, the sector-based model can stabilize parameter estimation in situations with competing directions, and sector weighting biases the DoA estimator, reducing directional fluctuations and stabilizing and improving performance. In general, this technique improves rendering situations consisting of highly spatial and directional sound events.

[0017] Combining the use of first-order (global) and higher-order (directionally local) sound field diffuseness estimates during rendering can improve performance in a coding framework. This is because the diffuseness level is crucial to the impression of the rendering, as it distributes the signal energy between the directional and diffuse rendering streams. See Figure 5a (block Ψ). Spatially averaged global diffuseness captures this feature of the sound scene accurately and with good stability, and therefore may actually provide better perceptual quality.

[0018] Lower bitrate scenarios can only transmit a single (primary) set of estimates, and therefore switching to a higher bitrate, enabling the proposed architecture, should not readjust the ratio of directivity to diffuseness of the rendered HOA signal. This is avoided by utilizing the global diffuseness Ψ to adjust the global directivity to diffuseness ratio. The directionally local sector diffuseness is then utilized to adjust the local sector directivity recoding.

[0019] The combination of global and sectoral diffuseness also enables diffuseness-dependent bit savings in the metadata, e.g., by limiting the quantization step of the directional parameters in sectors with dominant diffuse content: in sound scenes with high Ψ, only little energy is distributed to the directional stream, thus requiring only a coarse quantization of the directional parameterization.

[0020] Furthermore, the FOA can be assumed to be sufficiently restored at the decoder for sufficient bitrates, which makes it possible to restore a first-order estimate at the decoder, which in particular includes Ψ, and therefore does not need to be transmitted.

[0021] 2 shows an example related to the prior art. It can be seen that a FOA (first order Ambisonic) signal 202 is split in a signal splitter 204 between a single directional path 221 and a global diffuse path 205. The signal splitter 204 is adjusted by the global diffuseness Ψ of the FOA signal 202 (or alternatively adjusted to the complement of the global diffuseness Ψ of the FOA signal 202, which may be 1-Ψ).

[0022] In signal divider 204, the FOA signal 202 is scaled by a weight depending on the directionality of the signal (1-Ψ). In block 224, the omnidirectional pressure x is divided by 00 is applied to the FOA. The directional signal 226 is also transformed by applying a spherical harmonic function of DoA(Ω) in block 228. In the divider 204, the signal divider 204 also outputs a global diffuse signal 210, which is routed to the second path 205, for example, by weighting the FOA signal 202 with a weight conditioned by Ψ. In the energy compensator (208) (see (References)), the global diffuse signal 210 is obtained. In block 260, the global diffuse signal 210 and the directional signal 222 are added to obtain the HOA signal 262. The DoA Ω and the global diffuseness Ψ are obtained from the bitstream.

[0023] It is intended to more accurately model realistic sound scenes by resolving simultaneous multi-source scenarios, resulting in improved perceptual quality during HOA audio coding and spatial enhancement over current designs. Summary of the Invention [Means for solving the problem]

[0024] According to one aspect, there is provided an audio signal representation decoding unit for generating an expanded Ambisonic spatial audio representation from a compressed Ambisonic spatial audio signal representation representing an audio signal, the compressed Ambisonic spatial audio signal representation comprising at least one transport channel and side information, the side information comprising sound field parameters, the sound field parameters comprising, for each spatial sector of a plurality of spatial sectors, a directivity parameter providing information about a direction of arrival DoA in the spatial sector, and the sound field parameters comprising, for at least one spatial sector, a sector spreadness parameter providing information about a sector spreadness of the audio signal in the at least one spatial sector; an audio signal representation decoding unit including a plurality of sector decoding paths, each configured to decode a directional sector signal of the stretched Ambisonic spatial audio signal representation in each spatial sector by applying a spatial sector directivity parameter and a sector spread parameter to at least one transport channel or a sector signal derived from at least one transport channel; the audio signal representation decoding unit includes a global diffuse signal decoding path configured to derive a global diffuse signal by applying a global diffuseness parameter or other information related to the global diffuseness of the audio signal to at least one transport channel; An audio signal representation decoding unit includes a global diffuse signal inserter for combining the plurality of decoded directional sector signals and a global diffuse signal to output an expanded Ambisonic spatial audio signal representation.

[0025] In some examples, at least one transport channel may actually include multiple transport channels (or at least may be processed, for example, by upmixing, to obtain multiple transport channels). For example, at least one transport channel may actually include multiple transport channels upmixed from a first number of transport channels (which may be one or more) to a second number of transport channels (the second number of transport channels being more than the first number of transport channels and therefore typically multiple). Thus, even if the bitstream includes a single transport channel (or a specific number of transport channels), in some examples, the audio signal representation decoding unit may process the single transport channel (or the specific number of transport channels) to obtain multiple upmixed transport channels (more than the specific number of transport channels). Then, the directional path and the global diffusion signal decoding path are applied to the multiple upmixed transport channels.

[0026] According to one aspect, the audio signal representation decoding unit is configured to apply the sector spread parameter to at least one transport channel or a sector signal derived from the transport channel by weighting the transport channel in at least one sector decoding path using mixing weights derived from the sector spread parameter to derive a directional sector signal.

[0027] According to one aspect, the audio signal representation decoding unit is configured to weight at least one transport channel or sector signal derived from the transport channel using mixing weights that are positive coefficients received from or processed from the sector spreadability parameters or that are derived from the positive coefficients.

[0028] According to one aspect, the audio signal representation decoding unit is configured to weight, for at least one spatial sector, at least one transport channel or a sector signal derived from the transport channel using a mixing weight; The blending weights are or are derived from coefficients that indicate the sector directionality in a particular spatial sector.

[0029] According to one aspect, the audio signal representation decoding unit is configured to weight, for each spatial sector, at least one transport channel or sector signal derived from the transport channel using a mixing weight; The mixing weights are or are derived from coefficients that indicate the relative directivity of a signal in a particular spatial sector relative to the relative directivity of the spatial sector as a whole.

[0030] According to one aspect, the audio signal representation decoding unit is configured to weight at least one transport channel or a sector signal derived from the transport channel for at least one first spatial sector using a first mixing weight that is a coefficient indicative of a sector directivity in the first spatial sector or that is derived from the coefficient; and configured to weight at least one transport channel or sector signal derived from the transport channel using a second mixing weight for at least one second spatial sector; The audio signal representation decoding unit is configured to obtain second mixing weights obtained by interpolating a coefficient indicating sector directivity in the first spatial sector to a predetermined fixed value.

[0031] According to one aspect, the audio signal representation decoding unit is configured to derive each of the (N-1)th mixing weights from parameters described in the side information and to derive one Nth mixing weight by complementing the other (N-1)th mixing weights to a constant positive value, where N is the number of spatial sectors.

[0032] According to one aspect, the decoding unit, in each sector decoding path, calculates the DoA (Ω) in the spatial sector to extend the directional signal of the spatial sector to a higher Ambisonic order. s ) to apply a directivity parameter to the at least one sector signal by multiplying the at least one sector signal by a vector of spherical harmonics evaluated along

[0033] According to one aspect, the decoding unit is configured to apply a spatial filter to the at least one transport channel or a processed version of the at least one transport channel to limit the at least one transport channel to one spatial sector for each sector decoding path.

[0034] According to one aspect, the decoding unit comprises: x s =x s *Y(Ω s )=[x s *Y 00 (Ω),x s *Y 1-1 (Ω), x s *Y 10 (Ω), x s *Y 11 (Ω),...] where s denotes a spatial sector and x sis the transport channel or its processed version in a particular spatial sector s, and Ω s is the directivity parameter of a particular spatial sector s, and Ω s If Y, which is a function of [Y 00 (Ω s ), Y 1-1 (Ω s ), Y 10 (Ω s ), Y 11 (Ω s ),...Y nm (Ω s )], and Y nm (Ω s ) are spherical harmonics of order n and order m.

[0035] According to one aspect, the decoding unit of any of the previous aspects comprises: x H,s =(1-Ψ)*a s *Y(Ω s )*x s is configured to calculate at least one directional sector signal for at least a particular spatial sector using s is the sector spread parameter expressed as the relative sector directivity for at least one sector signal, and Y(Ω) is the DoAΩ in a particular spatial sector. s is a vector of spherical harmonics evaluated along

[0036] According to one aspect, the decoding unit is configured to read the global diffuseness parameter from the side information.

[0037] According to one aspect, the decoding unit is configured to estimate a global diffuseness parameter from at least one transport channel.

[0038] According to one aspect, the decoding unit applies a global diffuseness parameter or a global diffuseness weight obtained from information about the global diffuseness of the audio signal to weight at least one transport channel, thereby obtaining a global diffuseness signal version to be used in a global diffuseness signal decoding path; The method is configured to apply a second weight complementary to the global spreading weight to weight the at least one transport channel, thereby obtaining at least one global unspread signal to be processed in the multiple sector decoding paths.

[0039] According to one aspect, the decoding unit is configured to derive mixing weights for the global diffuse signal and the directional sector signals from a global diffuseness parameter or information about the global diffuseness of the audio signal.

[0040] According to one aspect, the decoding unit is configured to apply, for each sector decoding path, a weighting parameter to at least one transport channel that is complementary to a global spreading parameter used to derive the global spreading signal, such that at least the transport channel is weighted using the weighting parameter.

[0041] According to one aspect, the global diffuseness signal decoding path is configured to weight at least one transport channel by a global diffuseness gain, which is or is derived from a global diffuseness parameter or other information regarding the global diffuseness of the audio signal; Each of the multiple sector decoding paths is configured to weight at least one transport channel by a global directivity gain that is or is derived from a global diffuseness parameter or other information regarding the global diffuseness of the audio signal.

[0042] According to one aspect, the global diffusivity gain is 1+g(Ψ),

[0043]

number

[0044] where Ψ is or is derived from a global diffuseness parameter or other information about the global diffuseness of the audio signal, L is the Ambisonic input order, and H is the Ambisonic output order.

[0045] According to one aspect, the global diffusivity gain is 1+g(Ψ),

[0046]

number

[0047] where Ψ is or is derived from a global diffuseness parameter or other information about the global diffuseness of the audio signal, and f comp is the diffusion correction coefficient.

[0048] According to one aspect, the diffusion correction factor is:

[0049]

number

[0050] where l is the order of the spherical harmonics, L is the Ambisonic order of the input signal, H is a higher Ambisonic order, or the signal contains transport channels and channels generated through the use of a decorrelator, and m is the index of the spherical harmonics, ranging from -l to l.

[0051] According to one aspect, the range of values ​​of the global diffuseness gain is limited to a particular range of values ​​to prevent excessive deviation from the global diffuseness signal.

[0052] According to one aspect, the global diffuse signal decoding path includes an energy compensation unit that applies a gain to the global diffuse signal to adjust the energy distribution in order to obtain a more physically realistic Ambisonics output signal.

[0053] According to one aspect, the audio signal representation decoding unit comprises: a low-order operating mode in which, among the plurality of sector decoding paths, at least one sector decoding path is deactivated, and only one of the sector decoding paths is activated, and the side information does not include sound field parameters of the at least one deactivated sector decoding path; a high-order operating mode, in which all of the sector decoding paths are activated or at least fewer sector decoding paths are deactivated compared to the low-order operating mode, and the side information includes sound field parameters of all of the sector decoding paths as well as a global diffuseness parameter; The system is configured to switch between

[0054] According to one aspect, the audio signal representation is configured to convert the spatial audio signal representation from the at least one encoded transport channel to a decoded version of the at least one encoded transport channel.

[0055] According to one aspect, the audio signal representation comprises an EVS decoder that decodes the encoded at least one transport channel into a decoded version of the encoded at least one transport channel.

[0056] According to one aspect, the audio signal representation decoding unit is configured to transform the decoded Ambisonic spatial audio signal representation from the filterbank domain to the time domain.

[0057] According to one aspect, the audio signal representation decoding unit is configured to upmix at least one transport channel from a first number of transport channels to a second number of transport channels, the second number being greater than the first number.

[0058] According to one aspect, the audio signal representation decoding unit comprises a mixing matrix estimator configured to process the sound field parameters to derive a covariance matrix or other covariance information between different transport channels, the mixing matrix estimator being configured to reconstruct the mixing matrix or other mixing information from the covariance matrix or other covariance information and to apply the mixing matrix or other mixing information to the transport channels.

[0059] According to one aspect, the mixing matrix estimator is configured to process sound field parameters including DoA parameters and sector dispersity parameters of multiple spatial sectors and a global diffuseness parameter or other information related to global diffuseness in order to derive a covariance matrix or other covariance information between different transport channels; the mixing matrix estimator is configured to reconstruct a mixing matrix from the covariance matrix or other covariance information in order to use the sound field parameters in order to derive a covariance matrix or other covariance information for at least one frequency band; and the audio signal representation decoding unit is configured to derive a covariance matrix or other covariance information for at least one other frequency band without using the sound field parameters.

[0060] According to one aspect, the audio signal representation decoding unit is configured to derive, for at least one other frequency band, a mixing matrix or other mixing information from covariance information received from the side information.

[0061] According to one aspect, the sound field parameters are modified to achieve a rotation of the sound field represented by the output Ambisonic signal.

[0062] According to one aspect, an audio signal representation decoding unit according to any of the preceding aspects; a bitstream reader and an inverse quantizer configured to read a bitstream in which an encoded low-order spatial audio signal representation is present and to provide an audio signal representation decoding unit with a high-order spatial audio signal representation; An apparatus is provided comprising:

[0063] According to one aspect, an apparatus includes: The system further comprises a renderer for rendering an audio signal from the Ambisonic spatial audio signal representation.

[0064] According to one aspect, the apparatus further comprises an encoding unit for encoding the high-order spatial audio signal representation into a second spatial audio signal representation.

[0065] According to one aspect, there is provided an audio signal representation coding unit for encoding an input spatial audio signal representation representative of an audio signal into a compressed Ambisonic spatial audio signal representation representative of the audio signal, said audio signal representation coding unit comprising: an audio signal representation coding unit configured to downmix the input spatial audio signal representation to derive at least one transport channel; the audio signal representation coding unit is configured to derive side information, the side information including sound field parameters, the sound field parameters including, for each spatial sector of the plurality of spatial sectors, a directivity parameter providing information about a direction of arrival DoA in the spatial sector, and the sound field parameters including a sector diffuseness parameter providing information about diffuseness of the audio signal in at least one spatial sector; the audio signal representation coding unit includes a plurality of sector parameter estimators, each configured to process a particular sector signal of the input spatial audio signal representation in a particular spatial sector among the plurality of spatial sectors to derive information regarding directivity parameters and diffuseness of the audio signal in at least one spatial sector; The audio signal representation encoding unit includes a bitstream writer for encoding at least one transport channel and side information.

[0066] According to one aspect, the audio signal representation coding unit comprises a global diffuseness parameter estimator for estimating a global diffuseness parameter to be inserted in the side information.

[0067] According to one aspect, the audio signal representation coding unit is configured to refrain from writing a global diffuseness parameter in the bitstream.

[0068] According to one aspect, the audio signal representation coding unit is configured to estimate the relative directivity of each particular spatial sector with respect to the directivity of all spatial sectors and write (e.g., in side information) coefficients (e.g., denoted a1, a2, etc. hereinafter, which may be mixing weights) or information indicative of the relative directivity as sector diffuseness parameters (e.g., one sector diffuseness parameter for at least one of the plurality of spatial sectors, such as one sector diffuseness parameter for each spatial sector of the plurality of spatial sectors, or one sector diffuseness parameter for each of all spatial sectors except one of the plurality of spatial sectors).

[0069] In some examples, for each sector diffuseness parameter, it is possible to write each coefficient (a1, a2, etc.) or information indicating relative directivity (e.g., in the side information). In some examples, all but one coefficient or information indicating relative directivity is written (e.g., in the side information) because the sum of the coefficients (or information indicating relative directivity) may be known (e.g., 1), and one of the coefficients can be skipped and the decoder can reconstruct it, and the single coefficient or information indicating relative directivity is skipped. For example, a2+a1=1 may be, therefore, it is possible to simply write a1 as side information, and the audio signal representation decoding unit may derive a2 from a2=1−a1. Thus, in some examples, the side information may include all coefficients, and in some other examples, at least one coefficient (e.g., only a1) may be written, and at least one coefficient may be obtained from the first coefficient (e.g., as a2=1−a1).

[0070] According to one aspect, the audio signal representation coding unit is configured to estimate the relative directivity as comprising at least one of a first and a second spatial sector, denoted a1 and a2, respectively;

[0071]

number

[0072] and, a2=1-a1 where Ψ1 is or is obtained from sector spread information of the first spatial sector and Ψ2 is or is obtained from sector spread information of the second spatial sector.

[0073] According to one aspect, the audio signal representation coding unit comprises:

[0074]

number

[0075] Here, Σ j a j =1 where i denotes the ith specific spatial sector, j denotes the jth general spatial sector of the plurality of spatial sectors, and Ψ i and Ψ j denotes the sector diffuseness information of the i-th specific spatial sector and each j-th general spatial sector.

[0076] According to one aspect, the audio signal representation coding unit is configured to perform an active downmix of the audio signal or a processed version thereof using a downmix matrix or other downmix information calculated by a downmix information calculator, the downmix information calculator being configured to process the sound field parameters to derive the downmix matrix or other downmix information based on a global and sector diffuseness parameter and a directivity parameter for each spatial sector of the plurality of spatial sectors.

[0077] According to one aspect, the information matrix calculator is configured to perform inter-channel prediction to derive a downmix matrix or other downmix information based on an inter-channel covariance matrix or other inter-channel covariance information, the inter-channel covariance matrix or other inter-channel covariance information being derived from a directivity parameter and a sector spread parameter for each spatial sector of the plurality of sectors and a global spread.

[0078] According to one embodiment, the inter-channel covariance matrix C is the element C between Ambisonic channels with orders and indices l and l′, respectively, and Ambisonic channels with orders and indices l′ and m′, respectively. lm,l'm' and C lm,l'm' = (1-Ψ)*E x *a 2 *Y lm (Ω1)*Y l'm' (Ω1)+ (1-Ψ)*E x *(1-a) 2 *Y lm (Ω2)*Y l'm' (Ω2)+ +Ψ*σ 2 *E x *δ lm,l'm' is defined as calculated according to x is the signal energy, and δ lm,l'm' is the Kronecker delta which is 1 on the diagonal of the inter-channel covariance matrix and 0 off the diagonal of the inter-channel covariance matrix, Ω1 and Ω2 are the first and second directivity parameters, respectively, “a” is another parameter indicating the relative directivity, i.e., the ratio between the directivity in a spatial sector and the overall directivity of the entire spatial sector, or another information about the relationship between them, Ψ denotes the global diffuseness parameter, and σ is an energy scaling factor.

[0079] According to one aspect, the inter-channel covariance matrix or other inter-channel covariance information is calculated for each spatial sector by DoA(Ω1, Ω2, ..., Ω N ) and the spherical harmonic weighted energy and mixing weights (a1, a2, ..., a N ) and is based on

[0080] According to one aspect, the audio signal representation coding unit is further configured to transform the input spatial audio signal representation into a filterbank domain to derive a filterbank version of the input spatial audio signal representation; further configured to downmix a filterbank domain version of the input spatial audio signal representation to derive at least one transport channel in the filterbank domain; The filter bank domain is further configured to perform a filter bank synthesis of the at least one transport channel from the time domain.

[0081] According to one aspect, the audio signal representation coding unit is configured to downmix the input spatial audio signal representation using a channel selector to derive at least one transport channel by selecting a lower order channel from other higher order channels of the input spatial audio signal representation.

[0082] According to one aspect, the audio signal representation encoding unit is further configured to perform Enhanced Voice Services (EVS) encoding to provide an EVS encoded version of the at least one transport channel.

[0083] According to one aspect, a low-order operating mode in which, among a plurality of sector paths (e.g., sector coding paths), at least one sector path is deactivated and only one of the sector paths is activated, and the side information does not include sound field parameters of the at least one deactivated sector path; a high-order operating mode, in which among the plurality of sector paths, all of the plurality of sector paths are activated or at least fewer sector paths are deactivated compared to the low-order operating mode, and the side information includes sound field parameters of all of the plurality of activated sector paths as well as a global diffuseness parameter; An audio signal representation coding unit is provided that is configured to switch between

[0084] According to one aspect, the audio signal representation coding unit may be configured to select between a low-order mode of operation and a high-order mode of operation based on the bit rate, such that the low-order mode of operation is selected for a low bit rate and the high-order mode of operation is selected for a bit rate higher than the low bit rate.

[0085] According to one aspect, the audio signal representation coding unit comprises: the audio signal representation coding unit selecting a low-order mode of operation when measurements related to the quality of the network connection indicate low quality (e.g., high latency and / or high error rate, and / or low connection bandwidth, etc.); If a measurement related to the quality of the network connection indicates high quality, and the high quality is higher than low quality (e.g., low latency and / or low error rate, and / or connection bandwidth, etc.), the audio signal representation coding unit selects the high-order operating mode. Thus, the network controller may be configured to select between a low-order mode of operation and a high-order mode of operation based on measurements related to the quality of the network connection (e.g., latency-related measurements and / or error rate measurements, and / or connection bandwidth measurements, etc.).

[0086] (To perform the selection, measurements related to the quality of the network connection may be evaluated with respect to predetermined quality thresholds to classify the quality of the network connection. For example, to determine whether the quality is high or low, measurements related to the quality of the network connection may be evaluated with respect to at least one quality threshold to distinguish between high quality and low quality. For example, latency may be evaluated with respect to a latency threshold, e.g., to classify the quality as low if the average latency exceeds a latency threshold, and classify the quality as high if the average latency is below a latency threshold. Or, error rate may be evaluated with respect to an error rate threshold, e.g., to classify the quality as low if the average error rate exceeds an error rate threshold, and classify the quality as high if the average error rate is below an error rate threshold. Or, connection bandwidth may be evaluated with respect to a connection bandwidth threshold, e.g., to classify the quality as low if the average connection bandwidth is below a connection bandwidth threshold, and classify the quality as high if the average connection bandwidth is above a connection bandwidth threshold.)

[0087] According to one aspect, the audio signal representation coding unit comprises: the audio signal representation coding unit selecting a reduced mode of operation when the battery supply related measurement indicates a low battery supply of a battery powering the audio signal representation coding unit; If the battery supply-related measurement indicates a high battery supply that is higher than a low battery supply, the audio signal representation coding unit selects the high order operating mode. Thus, the power supply may be configured to select between a lower and a higher mode of operation based on battery supply-related measurements.

[0088] (To perform the selection, the battery supply may be evaluated with respect to predetermined battery supply thresholds (charge thresholds) to classify the battery supply and perform the selection based on the classification. For example, to determine whether the battery supply is high or low, the battery supply measurement may be evaluated with respect to at least one battery supply threshold (charge threshold) to distinguish between high and low battery supply.)

[0089] According to one aspect, the audio signal representation coding unit may be configured to select between a low-order mode of operation and a high-order mode of operation based on a feedback signal from a receiver (e.g., a decoding unit) to select the mode of operation requested in the feedback signal.

[0090] According to one aspect, an audio signal representation coding unit according to the previous aspect; a quantizer and a bitstream writer for writing the low-order spatial audio signal representation into a bitstream; An audio encoder is provided, comprising:

[0091] According to one aspect, there is provided a method for decompressing an Ambisonic spatial audio signal representation representing an audio signal, the compressed Ambisonic spatial audio signal representation comprising at least one transport channel and side information, the side information comprising sound field parameters, the sound field parameters comprising, for each spatial sector of a plurality of spatial sectors, a directivity parameter providing information about a direction of arrival DoA in the spatial sector, and the sound field parameters comprising, for at least one spatial sector, a sector spreadness parameter providing information about a sector spreadness of the audio signal in the at least one spatial sector; The method includes using a plurality of sector decoding paths, each of which decodes a directional sector signal of the Ambisonic spatial audio signal representation in each spatial sector by applying a spatial sector directivity parameter and a sector spread parameter to at least one transport channel or a sector signal derived from the transport channels; The method includes using a global diffuse signal decoding path to derive a global diffuse signal by applying a global diffuseness parameter, or other information regarding the global diffuseness of the audio signal, to at least one transport channel; The method includes combining a plurality of decoded directional sector signals and a global diffuse signal via a global diffuse signal inserter to output a stretched Ambisonic spatial audio signal representation.

[0092] According to one aspect, there is provided a method for encoding an input spatial audio signal representation representative of an audio signal into a compressed Ambisonic spatial audio signal representation representative of the audio signal, comprising: The method includes deriving at least one transport channel and side information, the side information including sound field parameters, the sound field parameters including, for each spatial sector of a plurality of spatial sectors, a directivity parameter providing information about a direction of arrival (DoA) in the particular spatial sector, and the sound field parameters including a sector diffuseness parameter providing information about diffuseness of the audio signal in the at least one spatial sector; The method includes using a plurality of sector parameter estimators, each sector parameter estimator processing a particular sector signal of the input spatial audio signal representation in a particular spatial sector of the plurality of spatial sectors to derive information about directivity parameters and diffuseness of the audio signal in at least one spatial sector; The method includes using at least one transport channel and encoding side information into a bitstream.

[0093] According to one aspect, a non-transitory storage unit is provided that stores instructions that, when executed by a processor, cause the processor to perform the method of the previous aspect.

[0094] According to one aspect, a compressed Ambisonic audio signal representation is provided comprising at least one transport channel and side information, the side information comprising sound field parameters, the sound field parameters comprising, for each spatial sector of a plurality of spatial sectors, a directivity parameter providing information about a direction of arrival (DoA) in the spatial sector, and the sound field parameters comprising, for at least one spatial sector, a sector diffuseness parameter providing information about the diffuseness of the audio signal in the at least one spatial sector and a global diffuseness parameter.

[0095] According to one aspect, there is provided a compressed Ambisonic audio signal representation, for example generated according to the method for encoding an input spatial audio signal representation described above. [Brief explanation of the drawings]

[0096] [Figure 1] FIG. 1 is a diagram illustrating an example of a linear basis function of an Ambisonic representation. [Figure 2] FIG. 1 illustrates an embodiment of the prior art. [Figure 3] FIG. 1 shows an example of how to divide a sphere into two sectors. [Figure 4] FIG. 4 shows the basis functions of FIG. 1 after filtering with one of the sectors in FIG. 3. [Figure 5a] FIG. 2 illustrates an example of an audio signal representation decoding unit according to the present disclosure. [Figure 5b] FIG. 2 illustrates an example of an audio signal representation decoding unit according to the present disclosure. [Figure 5c] FIG. 2 illustrates an example of an audio signal representation decoding unit according to the present disclosure. [Figure 6] FIG. 10 shows the results of a subjective listening test comparing the present invention with the prior art. [Figure 7] FIG. 2 illustrates an example of an audio signal representation coding unit according to the present disclosure. [Figure 8] FIG. 5B shows an example of an apparatus including the audio signal representation decoding unit of FIGS. 5a to 5c. [Figure 9a] FIG. 1 illustrates an example of the present technique. [Figure 9b] FIG. 1 illustrates an example of the present technique. [Figure 9c] FIG. 1 illustrates results obtained using the present technique. [Figure 9d-1] FIG. 1 illustrates results obtained using the present technique. [Figure 9d-2] FIG. 1 illustrates results obtained using the present technique. [Figure 9d-3] FIG. 1 illustrates results obtained using the present technique. [Figure 10] FIG. 2 illustrates an example of an audio signal representation coding unit according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0097] 7 and 10, each of which illustrates an audio signal representation encoding unit (700, 700b) (also referred to as an "encoder") for encoding an input spatial audio signal representation (702) representing an audio signal (e.g., in higher-order Ambisonics) into a compressed Ambisonic spatial audio signal representation (502, 802) representing the audio signal (702). The audio signal representation encoding unit 700, 700b may be configured to downmix the input spatial audio signal representation (702) (e.g., in a downmix stage 1700a or 1700b) to derive at least one transport channel (736). The audio signal representation encoding unit may be configured to derive side information (503). The side information (503) may include sound field parameters (e.g., 714, 718, 549, 529). The sound field parameters (e.g., 714, 718, 549, 529) may include, for each spatial sector of the plurality of spatial sectors, a directivity parameter that provides information about the direction of arrival (DoA) in the spatial sector. The sound field parameters may include a sector diffuseness parameter that provides information about the diffuseness of the audio signal (702) in at least one spatial sector (e.g., diffuseness parameters may be written into the audio signal representation 502, 802 for at least one spatial sector, but they may provide information about the diffuseness for the entire spatial sector). The audio signal representation encoding unit (700, 700b) may include multiple sector parameter estimators (712, 7211, 7212, 721n). Each sector parameter estimator (712, 7211, 7212, 721n) may be configured to process a particular sector signal (710, 7101, 7102, 710n) of the input spatial audio signal representation (702) in a particular spatial sector among the multiple spatial sectors to derive directivity parameters in at least one spatial sector and information regarding the diffuseness of the audio signal (702).The audio signal representation encoding unit may include a bitstream writer (750) that encodes at least one transport channel (73620) and side information (503), which may be understood as embodying a compressed Ambisonic spatial audio signal representation (502, 802).

[0098] 5a to 5c show examples of audio signal representation decoding units (500, 500b, 500c) (also referred to as "decoders") for generating an expanded Ambisonic spatial audio signal representation (562) from a compressed Ambisonic spatial audio signal representation (502) representing an audio signal, where the compressed Ambisonic spatial audio signal representation (502, 802) may be, for example, the compressed Ambisonic spatial audio signal representation (502, 802) generated by an audio signal representation encoding unit (700, 700b). As explained above, the Ambisonic spatial audio signal representation (502, 802) may include at least one transport channel (501) and side information (503). The side information (503) may include sound field parameters (e.g., 529, 549, 718). The sound field parameters may include, for each spatial sector of the plurality of spatial sectors, a directivity parameter (e.g., 529, 549, 718) that provides information about the direction of arrival (DoA) in the spatial sector. The sound field parameters may include, for at least one spatial sector, a sector diffuseness parameter (529, 549) that provides information about the sector diffuseness of the audio signal in the at least one spatial sector (as explained above, the diffuseness parameters may be in the audio signal representation 502, 802 for at least one spatial sector, but they may provide information about the diffuseness for the entire spatial sector). The audio signal representation decoding unit may include multiple sector decoding paths (521, 541). Each sector decoding path (521, 541) may be configured to decode a directional sector signal (532, 552) of the expanded Ambisonic spatial audio signal representation (562) in each spatial sector by applying a spatial sector directivity parameter (529, 549) and a sector diffuseness parameter (529, 549) to at least one transport channel (501) or a sector signal (528, 548) derived from at least one transport channel.The audio signal representation decoding unit may include a global diffuseness signal decoding path (505) that derives a global diffuseness signal (510) by applying a global diffuseness parameter (507, 507′, Ψ) or other information related to the global diffuseness of the audio signal to at least one transport channel (501). The audio signal representation decoding unit may include a global diffuseness signal inserter (560) that combines a plurality of decoded directional sector signals (532, 552) and the global diffuseness signal (510) to output an expanded Ambisonic spatial audio signal representation (562).

[0099] The units discussed above are described in more detail below.

[0100] 5a shows an audio signal representation decoding unit 500. The audio signal representation decoder unit (audio signal representation decoding unit) 500 may receive at an input a compressed Ambisonic spatial audio signal representation (e.g., an FOA signal) 502 and provide at an output an expanded Ambisonic spatial audio signal representation 562 (e.g., an HOA or higher-order expanded Ambisonic spatial audio signal representation). (The FOA signal 502 may be replaced by a lower-order Ambisonic signal, and the HOA signal 562 may be a higher-order Ambisonic signal than the low-order Ambisonic signal 502.)

[0101] The compressed Ambisonic spatial audio signal representation 502 is composed of at least one transport channel 501 (possibly mathematically x L5a). The at least one transport channel 501 may, for example, include a downmixed version of the original audio signal representation (of the audio signal). Generally speaking, the at least one transport channel 501 may be understood as having channels downmixed with respect to the original channels of the audio signal 702. Each channel may be an Ambisonic component (Ambisonic components are shown in FIG. 1). For example, if the compressed Ambisonic spatial audio signal representation 502 is an FOA signal, there may be multiple channels, for example, four channels. Each transport channel 501 may be provided in or converted from the filter bank domain. In the following, reference is often made to at least one transport channel, but this is also valid for multiple channels (for example, four or more channels). In particular, the transport channel 501 may be processed via the elements of FIG. 5a to become the decompressed spatial audio signal representation 562.

[0102] If the input compressed Ambisonic spatial audio signal representation 502 is not in the filterbank domain, there may be a filterbank (not shown in Figure 5a) upstream of the elements shown in Figure 5a that converts the compressed Ambisonic spatial audio signal representation into the filterbank domain. In some examples, there may be another filterbank synthesizer (also not shown in Figure 5a) downstream of the elements shown in Figure 5a, for example to provide an expanded spatial audio signal representation 562 in the time domain.

[0103] At least one (or two or more) transport channel 501 (or compressed Ambisonic spatial audio signal representation 502) may be an HOA signal, or more generally, a lower-order Ambisonic signal. One task of the audio signal representation decoder unit 500 (audio signal representation decoding unit) may be to obtain an expanded Ambisonic spatial audio signal representation 562 as an HOA, or at least a higher-order Ambisonic signal, which corresponds to the HOA signal 702 input at the encoder 700 or 700b and gives reliable audio information of this HOA signal 702.

[0104] The compressed Ambisonic spatial audio signal representation 502 may include side information 503. The side information 503 may include sound field parameters. In an example, all time-frequency tiles within the same spatial sector may or may not share at least some of the sound field parameters. For example, some sound field parameters may be the same for all bands. In some examples, bands may be grouped together to save on metadata. Also, for some signals, parameters may be the same for some of all bands (although in general they may be different for each band). In some cases, different bands may have different sound field parameters.

[0105] The sound field parameters 529, 549 may include at least one directivity parameter for each specific spatial sector among the multiple spatial sectors. For example, if there are two spatial sectors, there may be two directivity parameters for each frequency band (one for each sector). The sector index is denoted by s. The total number of sectors is N. Here, N=2 (or sometimes N≧2 for generality) is often illustrated. The space may be divided into spatial sectors. The positions of the spatial sectors may be fixed (i.e., the priority may be known by both the encoding unit 700, 700b and the decoding unit 500). The directivity parameter may be information about the direction of arrival (DoA) in a specific spatial sector, or may provide this information in other ways. The DoA is denoted by the symbol Ω for a specific spatial sector s. s where s indicates a particular sector. For example, if we have two spatial sectors s=1 and s=2, we may have Ω1 and Ω2. For more than two spatial sectors, we also have Ω3, Ω4, etc. Thus, at least one directivity parameter 529, 549 may be provided. Thus, for each spatial sector, a specific directivity parameter may be defined (e.g., for each time-frequency tile). In contrast to the prior art shown in the example of FIG. 2 (where there is only a single DoA for the entire space), here there is one directivity parameter for each spatial sector, and there are more than one spatial sector.

[0106] The sound field parameters 529, 549 may also include at least one sectoral diffuseness parameter (529, 549 using the same reference numbers used for the directivity parameters) that may provide information about sectoral (local) diffuseness or, complementary, sectoral (local) directivity. The sectoral diffuseness parameter is often expressed as Ψ swhere s denotes the sector, which in the case of two sectors may be expressed as Ψ1 and Ψ2 (or 1-Ψ1 and 1-Ψ2 if sector directivity is referred to). Another name for "diffusivity" may be, for example, the "diffusivity energy ratio," Ψ = (diffusivity energy) / (total energy) (where " / " means division). The global diffuseness (or global diffuseness energy ratio) may be Ψ = (diffusivity energy in space) / (total energy in space), and the sector diffuseness (or sector diffuseness energy ratio) may be Ψ s = (diffused energy in sector s) / (total energy in sector s).

[0107] Here, "directivity" should be understood as a complementary concept to diffuseness ("global diffuseness" and "sector diffuseness"). Whether referring to Ψ1 or Ψ2 (from the perspective of diffuseness) or 1-Ψ1 or 1-Ψ2 (from the perspective of "directivity"), information indicating "sector diffuseness" exists, since 1-Ψ1 or 1-Ψ2 also indicates Ψ1 or Ψ2, and vice versa (the same applies to global diffuseness Ψ and its complementary information 1-Ψ). Another name for "directivity" is, for example, "directed energy ratio," and diffuseness, which is complementary to diffuse energy ratio (e.g., 1-Ψ = (diffuse energy) / (total energy)).

[0108] More specifically, a distinction is made here between "sector directivity" (1-Ψ1, 1-Ψ2) and "directional information" (e.g., provided in terms of Ω1 and Ω2), where "directional information" and DoA provide geometric information about the direction of a signal (e.g., intensity vectors) without specifically indicating weight information or energy information or intensity or pressure information or weight, while "directivity" (1-Ψ1, 1-Ψ2) refers to concepts such as, for example, weight, intensity, energy, pressure, etc., that characterize sound, without giving information about DoA. Generally speaking, the more locally diffuse an audio signal is within a spatial sector, the less directional the audio signal is within the same spatial sector.

[0109] The side information 503 may also include, for example, sound field parameters, global diffuseness parameters, or other global diffuseness parameters (507, 507′, Ψ), or other information regarding the global diffuseness of the audio signal. The global diffuseness parameter is generally denoted by Ψ without an index and is a global characteristic describing the input signal. The global diffuseness parameter Ψ may therefore provide information for weighting the FOA transport channels 501 (e.g., see below in divider 504) to derive the diffuseness component 506 in path 505 (also denoted as “diffuse component” in FIGS. 1 and 4 ). Another way to provide information regarding the global diffuseness of the audio signal may be to indicate 1−Ψ (or B−Ψ, e.g., a fixed, e.g., a priori known, B>0), where 1−Ψ is complementary information to the global diffuseness, but is still information regarding the global diffuseness.

[0110] Thus, the global diffuseness parameters (507, 507', Ψ) or other information regarding the global diffuseness of the audio signal may also be estimated in some cases, for example when the compressed Ambisonic spatial audio signal representation 502 has four or more transport channels 501. In other situations, the global diffuseness parameters (507, 507', Ψ) or other information regarding the global diffuseness of the audio signal may be encoded in the side information 503.

[0111] At least one transport channel can be divided into a globally diffused signal (e.g., weighted by Ψ) and a non-globally diffused signal (e.g., weighted by 1-Ψ). Nevertheless, the inventors understand that a non-globally diffused signal is not necessarily an "omnidirectional signal" (i.e., not necessarily fully directional), is not necessarily uniquely distributed in a single DoA, and may be distributed between local directional components (sector-directional components) and local diffuse components (sector-diffuse components) among multiple sectors.

[0112] It will be shown that the inventors also understand that it is not strictly necessary to calculate (or write into the sound field parameters) both the sector directional component and the sector diffuseness component for each sector. In contrast, it is more easily possible to measure the directivity of each spatial sector relative to the sum of the directivities of all spatial sectors for each sector and derive a relative directivity for each sector. By weighting at least one transport channel 501 for each spatial sector by a mixing weight derived from the relative directivity of that spatial sector, it is easily possible to derive a sector directional signal that takes into account both its DoA and its sector diffuseness. (It will be shown that the relative directivity can be the ratio between the sector directivity in a spatial sector and the sum of the sector directivities across the spatial sector.)

[0113] In the following, we will often refer to sector diffusivity parameters. Relative directivity can be an example of a diffusivity parameter.

[0114] As can be seen in Figure 5a, at least one transport channel 501 is subjected to a splitter 504 or another element to which weights conditioned by global diffuseness parameters (507, 507', Ψ) or other information about the global diffuseness of the audio signal are applied. The splitter (or other element) 504 splits the compressed Ambisonic spatial audio signal representation 502 into two signals to output a global diffuse signal 506 (in the compressed FOA version) and a remaining global non-diffuse signal 520 (in the compressed FOA version). The global diffuse signal 506 may be understood as being weighted by a weight (e.g., Ψ) that increases as diffuseness increases (e.g., high diffuseness results in a high Ψ, complete diffuseness results in Ψ=1 or another maximum value, low diffuseness results in a low Ψ, no diffuseness results in Ψ=0, and at Ψ>0.5, the diffuse signal 506 tends to dominate the global non-spread signal, while at Ψ<0.5, the remaining global non-spread signal 520 tends to dominate the diffuse signal 506). The global non-spread signal 520 may be understood as being obtained from a transport channel 501 weighted by a weight (e.g., 1-Ψ) that increases as global diffuseness decreases (i.e., increases as global directionality increases). The global non-spread signal 520 may have residual energy. However, the energy of the global non-spread signal 520 may be locally spread within a single sector. Therefore, the global unspread signal 520 is also filtered into multiple sector signals (528, 548), and each sector signal (528, 548) is continued up to any higher Ambisonic order using spherical harmonics of these orders to become a directional sector signal (532, 552).

[0115] In the global diffuse signal decoding path 505, in block 508 (energy compensator), a gain 1+g(Ψ) can be provided to weight the global diffuse signal (component) 506 so that its energy matches the energy of a physically correct HOA signal (see (References)). In some cases, the gain 1+g(Ψ) can be

[0116]

number

[0117] where Ψ is or is obtained from the global diffuseness parameter (507, 509) or other information about the global diffuseness of the audio signal, L is the Ambisonic input order, and H is the Ambisonic output order (other formulas are possible).

[0118] Alternatively, the gain may be

[0119]

number

[0120] where the diffusion compensation factor can be selected as

[0121]

number

[0122] where l is the order of the spherical harmonic function, L is the Ambisonic order of the input signal or a signal comprising transport channels and, optionally, channels generated through the use of a decorrelator, m is the index of the spherical harmonic function and takes values ​​from -l to l, and H is a higher Ambisonic order.

[0123] The range of values ​​for the global diffuseness gain may be limited to a particular range of values ​​to prevent excessive deviation from the global diffuseness signal (506).

[0124] The energy compensation unit 508 may apply a gain to the global diffuse signal 506 to adjust the energy distribution in order to obtain a more physically realistic Ambisonics output signal.

[0125] Note that it is generally assumed that 0≦Ψ≦1 (where Ψ=0 if the signal is completely directional and Ψ=1 if the signal is completely diffuse, and in some instances 1 may be replaced by a value B>0). The gain amplifies the FOA global diffuse signal (component) 506 via a gain 1+g(Ψ). In particular, higher diffuseness (e.g., Ψ closer to 1) implies higher gain than lower diffuseness (e.g., Ψ closer to 0).

[0126] 5a shows that the global diffuseness parameters (507, 507', Ψ), or other information about the global diffuseness of the audio signal, may be obtained from the side information 503 as parameter 507, or alternatively may be estimated (e.g., if the signal is Ambisonics or multi-channel) as 507' and / or 509' (507' and 509' may be the same) in an optional diffuseness estimator 570, e.g., using pseudo-intensity vector or covariance-related techniques. The diffuseness 507' (509') may be obtained by the optional diffuseness estimator 570 from the intensity vector and the average energy (this is the method adaptively used for DirAC).

[0127] The output of the energy compensation block 508, here designated 510, is the global diffuse signal 510 of the HOA signal, which is the diffuse component of the HOA output signal. Typically, this contributes only to the primary channel of the higher-order output signal.

[0128] In parallel with the processing in the global diffusive path 505, the global undiffused signal 520 (e.g., resulting as output 520 from divider 504 after FOA signal 501 has been scaled by (1-Ψ)) may be processed in multiple sector decoding paths 521, 541. For simplicity, FIG. 5a shows only two sector decoding paths 521 and 541. However, in general, there may be any number of sector decoding paths. In some implementations, N=2 sector decoding paths may be a reasonable design choice, representing a good tradeoff between the need to have good results and the need to keep computational complexity low.

[0129] The global unspread signal 520 may be subjected to spatial filtering in a spatial filtering stage 574. The inputs of the spatial filtering stage 574 are denoted 522 and 542 (which may be equal to each other and to the global unspread signal 520), and each of the inputs 522 and 542 enters a respective spatial filtering block 524, 544. The spatial filtering blocks 524, 544 are part of the spatial filtering stage 574, and each spatial filtering block filters the global unspread signal 520 to restrict the global unspread signal 520 to a particular spatial sector in each sector decoding path. Thus, at the output of the spatial filtering block 524 in path 521, the transport channels (in their sector-restricted version 528) are restricted to sector s=1, and at the output of the spatial filtering block 526 in sector decoding path 522, the transport channels (in their sector-restricted version 548) are restricted to sector s=2. To obtain the spatial filtering, the spatial filtering stage 574 may perform beamforming. Downstream of the spatial filtering stage 574, the sector signal 528 for spatial sector s=1 differs from the sector signal 548 for spatial sector s=2 because they are confined to a different spatial sector.

[0130] In particular, the spatially filtered signals 528, 548 of each sector decoding path 521, 541 can be understood to still be subject to another subdivision between the sector diffuse component and the DoA component; the sector signal simply lacks the global diffuse component (signal 510) that has already been polished out in the divider 504. (The global diffuse component can be considered to act as a common mode signal that has been removed in the divider 504.) Thus, each spatially filtered signal 528, 548 output by the associated block 526, 546 can be considered a sector signal that provides signal information about a particular spatial sector.

[0131] The spatial filtering stage 574 may be instantiated by multiple spatial filters in blocks 524, 544, etc. In each of blocks 524, 544, etc., beamforming may be performed for each spatial sector. In some examples, these may include:

[0132]

number

[0133] where w contains the beamforming weight vector for spatial sector s, and x L is the signal 528, 548 output by block 574, and "T" represents the transpose operator. The beamforming weight vectors may be known a priori by the decoder. In particular, w T s can be an operator in an abstract representation with multiple elements, each element having a weight

[0134]

number

[0135] (for example,

[0136]

number

[0137] )

[0138] In the subsequent sector signal processor stage 572 (including sector signal processor blocks 528, 548), the sector signals 528, 548 (processed transport channel, spatially filtered signal, etc.) are each converted into a spatial sector DoA Ω s (i.e., the local DoA within a particular spatial sector, e.g., as indicated in the sound field parameters 529, 549 of the side information 503). x s =Y(Ω s )*x s =[x s *Y 00 ,x s *Y 1-1 ,x s *Y 10 ,x s Y,...] where the scalar value x s is one of the sector signals 528, 548 (e.g.,

[0139]

number

[0140] , s denotes a particular spatial sector. The scaling by 1-Ψ (applied by divider 504) reduces the sector signal x s is not shown explicitly here because it enters the equation via Y(Ω s ) are the spatial sectors DoAΩ sis a vector of spherical harmonics (e.g., calculated by a decoder or read from a table) that allows reconstructing the higher-order directional sector signals 532, 555 along x s is the vector of decoded directional components of spatial sector s at the HOA.

[0141] The components of the vector are real spherical harmonics Y in Ambisonics Channel Numbering (ACN) order. l,m (Ω) (where Ω is, for example,

[0142]

number

[0143] These can be:

[0144]

number

[0145] (See References) (where "|...|" denotes absolute value, i.e., |-1|=+1, |0|=0, and |+1|=+1), and the associated Legendre polynomials

[0146]

number

[0147] , and is defined as a regularization term for both Legendre and trigonometric functions that takes the following form for SN3D ((References), (References)):

[0148]

number

[0149] For an Ambisonic order L, the subscripts l and m range from l=0,..,L and m=-1,..,l, respectively, where σm is 1 for m=0 and 0 otherwise, and '!' denotes factorial.

[0150] Thus, the spatially filtered signals 528, 548 may be subjected to a sector signal processor stage 572, which may include multiple blocks 530, 550 for paths 522, 542, to obtain directional sector signals 532, 552 (in higher-order Ambisonic format). For example, sector signal processing block 530 may be applied to the filtered signal 528 output by block 524, and sector signal processing block 550 may be applied to the signal 548 output by block 544 for path 541. This may be repeated, for example, for each spatial sector s. By operating accordingly, each block 530, 550, etc. of sector signal processor stage 572 may process the Ω instantiated in Ω1 and Ω2 for paths 521, 541, respectively. s It is shown that sector diffuseness parameters (e.g., Ψ1 and Ψ2 or a1, a2 as discussed below) and / or DoA for spatial sector s, such as σ, ...

[0151] For example, in the case of two spatial sectors (s=2), coefficients (mixing weights) a1 and a2 can be used, each of which is expressed as a ratio indicating, for example, the sector directivity 1-Ψ1 (respectively, 1-Ψ2) to the sum of the sector directivities of all sectors 1-Ψ1+1-Ψ2 (respectively, the same 1-Ψ1+1-Ψ2). Examples are:

[0152]

number

[0153] and

[0154]

number

[0155] In this case (because s=2), a2=1-a1 Therefore, a1 and a2 are complementary to 1 (or another B>0 in other examples).

[0156]

number

[0157] a2=1-a1 At least one of a1, a2, b1, b2, c2, c3, c4, c5, c6, c7, c8, c9, c10, c11, c12, c13, c14, c15, c26, c27, c28, c39, c40, c41, c52, c53, c64, c75, c86, c97, c98, c99, c99, c10, c11, c22, c12, c23, c24, c25, c39, c40, c54, c65, c76, c87, c9 ... j If the sum of a1, a2, ..., and b is 1 (or another B>0), then the Nth relative directionality is 1-(a1+a2+...+a N-1 ) can simply be encoded to obtain n-1 relative directivities.

[0158] Coefficients a1, a2 (generally a s (also denoted as DoA sector DoAΩ) s (i.e., the local DoA within a particular spatial sector). x H,nm,s =(1-Ψ)*a s *Y nm (Ω s )*x s In this equation, 1-Ψ is applied in divider 504 and x s is applied in the spatial filtering stage 574, and a s *Y nm (Ω s ) may be applied in the stage sector signal processor 572. However, different processing may be performed.

[0159] Nevertheless, the directional sector signals 532, 552 (at least in some instances) are represented by the following terms: Space Sector DoAΩ s Spherical harmonic function Y evaluated along nm (Ω s ) (or other information that allows DoA to be applied to the transport channel), the global directivity 1-Ψ (or another global diffusivity information that allows polishing the global diffusivity component from the transport channel), Coefficient a s (or another sector diffusivity parameter) It is important to note that in certain cases, a s can be considered as the relative sector orientation of the current sector s to the whole of section n.

[0160] Essentially, in sector decoding paths 522, 542, etc., directional sector signals 532, 552 are decoded according to their relative sector directivities a s Then, all of them (520, 522, 542) are weighted by the global directivity 1-Ψ. In this way, they also take into account the sectoral spread of each.

[0161] Other types of coefficients different from a1 and a2 may also be used. For example, the diffusivity parameters may directly indicate, for example, Ψ1 or 1-Ψ1 and / or Ψ2 or 1-Ψ2.

[0162] For three or more sectors, a s (with s>2) may be used (possibly with the condition Σ s a s =1 or Σ s a s =B>0 can be given).

[0163] The coefficients a1 and a2 may be applied to the spatially filtered signals 528, 548, etc. An example of applying the coefficients is, for example, x H,nm,s =a s *x s *Y(Ω s), thereby obtaining directional sector signals 532, 552, etc.

[0164] Coefficient a (applied to different spatial sectors s=1, 2...) s Thanks to the application of the method, it is possible to provide different diffusions for different sectors.

[0165] For example, if the signal 522 in the first spatial sector s=1 is more directional relative to the second spatial sector s=2, then the coefficient a1 will be higher. Thus, if the signal in sector s=1 (path 521) is very directional and the signal in sector s=2 is locally very diffuse, then a1 will tend to be greater than a2; if the signal in sector s=1 (path 521) is very diffuse and the signal in sector s=2 is very directional, then a1 will tend to be greater than a2. <a2となる。

[0166] Therefore, the coefficient a s gives information about the sector diffusivity (in a particular spatial sector) and so can be considered to provide diffusivity information (and thus be a sector diffusivity parameter). s is the sector directivity of sector s relative to the sum of the sector directivities of all spatial sectors (i.e., relative directivity). A more directional sector will have a higher (e.g., closer to 1), a s , and sectors that are more locally diffuse have lower (e.g., closer to 0), a s It has.

[0167] Coefficient a s is (at least for other directions in the same spatial sector) DoAΩ s, where the weights tend to be higher if the signal is very directional in spatial sector s (and tend to be lower if the signal is locally very diffuse in spatial sector s), and the weights tend to be higher than another sector s2 if the signal is more directional in spatial sector s than in other sectors s2 (and tend to be lower than another sector s2 if the signal is more diffuse in spatial sector s than in other sectors s2). (The transport channel transformation is x nm,s =Y(Ω s )*x s =[x s *Y 00 ,x s *Y 1-1 ,x s *Y 10 ,x s *Y 11 It should be noted that the relationship is obtained from [,...].

[0168] Generally speaking, the coefficient a s may be an example of a mixing weight derived from the sector spreadability parameter (e.g., it may be the sector spreadability parameter itself). s The higher the ,the more mixing weight is applied to a particular path.

[0169] Essentially, it is possible to overcome the problems and challenges of the prior art beyond the obstacles of the standard Ambisonic model: multiple directional sound sources within the same time-frequency tile and specular reflections are therefore considered.

[0170] It should be noted that the directional signals 522, 542, as well as their versions 532, 552, are HOA signals. The vector of spherical harmonics Y(Ω) can be easily evaluated in any Ambisonic order. Therefore, the signal can be reconstructed in its original recorded order, or artificially extended to higher orders to create a better listening experience.

[0171] The audio signal representation decoding unit 500 may include a global diffuseness signal inserter 560. The global diffuseness signal inserter 560 may insert a global diffuseness (510) into the multiple decoded sector signals (532, 552, x H,nm,s ) with the global diffuse signal 510. Thus, the output of the global diffuse signal inserter 560 may be a compressed Ambisonic spatial audio signal representation 562.

[0172] Therefore, a signal 559 intended to be a juxtaposition of this directional signal 532 , 552 etc. and of the global diffuse signal 510 output by the energy compensation block 508 is here indicated with the reference numeral 559 .

[0173] In summary, the audio signal representation decoding unit 500 receives as side information 503: For each particular spatial sector, Directivity parameters (e.g., 529, 549, Ωs) that provide information about the direction of arrival (DoA) in a particular spatial sector; Sector diffuseness parameters (e.g., 529, 549, Ψ1, Ψ2, a1, a2, etc.) that provide information about the sector diffuseness of the audio signal in a particular spatial sector; sound field information including The global diffuseness parameters (507, 507', 509', Ψ) or other information regarding the global diffuseness of the audio signal (which may or may not be part of the side information 503 and / or may or may not be part of the sound field parameters or may be estimated, for example, by a global diffuseness estimator 570) may be used to generate an expanded Ambisonic spatial audio signal representation 562 from the compressed Ambisonic spatial audio signal representation 502 representing the audio signal.

[0174] These parameters can be easily applied to at least one transport channel 501 (in the FOA version) of the audio signal representation 502 to obtain a stretched HOA version 562 of the audio signal. In different sector decoding paths (521, 541, etc.), spatially filtered versions (528, 548) of the transport channel 501 are obtained, with each spatially filtered version (528, 548) representing the audio signal within a particular spatial sector. After each spatially filtered transport channel 528, 548 is continued into an HOA signal using a spherical harmonic function evaluated at the DoA for each sector, it is possible (in some examples) to apply a mixing weight to each sector signal 528, 548 that weights the sector signal 528, 548 according to the sector directivity of the audio signal in the particular sector (the mixing weight can be the relative directivity of each spatial sector to the sum of the directivities of all spatial sectors).

[0175] 8 shows an example of an apparatus 800 including a compressed Ambisonic spatial audio signal representation 502, which renders an audio signal (as a rendered audio signal 814) or a transcoded audio signal (as a transcoded signal 816) from the compressed Ambisonic spatial audio signal representation 502. Furthermore, the compressed Ambisonic spatial audio signal representation 502 may also be obtained from a bitstream 802 (a coded signal). The apparatus 800 may have a bitstream reader (coded signal reader) and an inverse quantizer 804, which may read the bitstream 802 (encoding the compressed Ambisonic spatial audio signal representation 502 or 502b) and provide the compressed Ambisonic spatial audio signal representation 502 or 502b to the audio signal representation decoding unit 500 (or 500b). The expanded Ambisonic spatial audio signal representation 562 may be output by the audio signal representation decoding unit 500 or 500b to a renderer 812 for rendering the audio signal 562 into an audio signal 814 (which should generally be the best possible reproduction of the original audio signal 702), or to an encoding unit 813, which may re-encode the audio signal Ambisonic spatial audio signal representation 562 into a different spatial audio signal representation 816. The different compressed Ambisonic spatial audio signal representation 816 may also be stored and / or transmitted to another device or unit. In this way, a transcoder is realized by the apparatus 800, if the renderer 812 is not used to obtain the signal 814 but is instead obtained by the encoding unit 813 to obtain the second spatial audio signal representation 816. In some examples, neither the renderer 812 nor the encoding unit 813 is present, and the output is simply the expanded Ambisonic spatial audio signal representation 562.

[0176] 10 shows, for example, an audio signal representation encoding unit (e.g., encoder) 700b that can be used to provide a bitstream (encoded signal) 802. (Generally speaking, the only metadata to be provided to the audio representation decoding unit 500 is the compressed Ambisonic spatial audio signal representation 502, as well as a number of directivity parameters and a parameter indicative of the sector spread, which may vary in different spatial sectors.) The audio signal representation encoding unit 700b, when encapsulated within the bitstream (coded signal) 802, enables the compressed Ambisonic spatial audio signal representation 502 to be provided.

[0177] The audio signal representation encoding unit 700b in FIG. 10 may be input with an audio signal (input audio signal representation representing an audio signal) 702, which may be, for example, an Ambisonic signal in the time domain (the audio signal representation encoding unit 700b may, for example, include a converter from a non-Ambisonic time-domain version to a higher-order Ambisonics HOA time-domain upstream of the HOA signal 702 in FIG. 10, although not shown in the figure). Furthermore, the input audio signal representation 702 may be obtained from a version obtained from a microphone or may be synthesized. Thus, the input audio signal representation 702 may generally be an uncompressed HOA representation of the audio signal. Therefore, the audio signal representation encoding unit 700b may compress the input audio signal representation 702 to an FOA (or at least a lower-order Ambisonic) compressed version 502 (802) of the input audio signal representation 702 in order to represent the same audio signal in a compressed version. It is shown that the encoded audio signal representation 502 may include at least one transport channel 501 (in one of versions 736 or 739) and side information 503, such as sound field parameters (e.g., as discussed above and below). In particular, the at least one transport channel 501 may represent a downmixed version of the HOA signal 702 (e.g., the at least one transport channel 501 in version 736 may have a selected channel amount with respect to the HOA signal 702).

[0178] The high-order Ambisonic (HOA) audio signal representation coding unit 700b may be provided to an analysis filterbank 704 to obtain a HOA signal version 706 of an input audio signal representation 702 in the filterbank domain, i.e., the time-frequency domain (such that the audio signal is subdivided into time-frequency tiles). The filterbank domain version 706 of the input audio signal representation 702 may be provided to a spatial filter stage 708. The spatial filtering stage 708 may perform beamforming, for example, by applying beamforming weights to the filterbank domain HOA signal 706. The HOA signal 706 may correspond to the expanded HOA signal 562 of FIG. 5a. The spatial filtering stage 708 may be instantiated with one spatial filter 7071, 7072, ..., 707n for each spatial sector (e.g., if there are two spatial sectors, there are two filters, i.e., N=2, and generally N>1). Each spatial filter 7071, 7072, ..., 707n may divide the audio signal 706 into spatial sectors (e.g., an N=2 spatial sector may be two hemispheres, or may define some other division of space). What is obtained in the spatial filtering stage 708 is a spatially filtered Ambisonic expanded signal 710 formed by several sector directional signals 7101, 7102, ..., 710n (one for each s spatial sectors of N>1 spatial sectors). The sector directional signals 7101, 7102, ..., 710n may correspond to the sector directional signals 532, 552 of Figure 5a, and the spatially filtered Ambisonic signal 710 may correspond to the signals 528, 548 of Figure 5a.

[0179] The spatially filtered version of the stretched HOA signal 710 may be provided to a sector parameter estimator stage 712, which may include multiple sector parameter estimators 7211, 7212, 721n, each of which may be configured to derive sound field parameters 7141, 7142, ..., 714n from the signals 7071, 7072, ..., 707n, respectively. Essentially, each value 7141, 7142, 714n represents DoA directionality information (e.g., Ω1, Ω2, ..., Ω N , ..., N) and local (sector) diffusivity information for each particular spatial sector 1, 2, ..., N (e.g., sector diffusivities Ψ1, Ψ2, ..., ΨN, and / or complementary local directivities 1-Ψ1, 1-Ψ2, ..., 1-Ψ N (In some cases, not all sector diffuseness information is calculated, e.g., it is possible to actually calculate a diffuseness parameter for each of N-1 spatial sectors out of all N spatial sectors.)

[0180] In parallel, a global diffuseness estimator 7129 (in the global diffuseness path) may be provided to provide a global diffuseness parameter (e.g., information on global diffuseness), here denoted 7149. The parameters 714 (7141, 7142, ..., 714n), i.e., the directivity and / or diffuseness parameters, may then be coded in the bitstream (coded signal) 802 (502), either directly or in a processed version, as sound field parameters coded in the side information 503. A parameter converter unit 716 (if present) may provide the directivity and diffuseness parameters 718 in processed form. If a parameter converter is provided, it may be, for example, coded using the equations

[0181]

number

[0182] and / or

[0183]

number

[0184] (As explained above, for N=2 spatial sectors, the coding of a1 or a2 may be skipped.) Thus, parameters 714 (7141, 7142, ..., 714n, 7149) and / or 718 may be, or may be processed to be, side information 503 (529, 549, 507).

[0185] Thus, the parameter converter unit 716 may convert the sector spread parameter from a first representation 714 that associates with each particular sector component information indicative of the sector spread (Ψ1, Ψ2) to a second representation 718 that associates with a particular sector signal information (a1, a2) indicative of the relative directivity of the sector signal with respect to the directivity of the sector signal as a whole. (The parameter converter unit 716 may not be necessary in some cases, for example, if the sector spread is written directly into the bitstream 802.)

[0186] The parameter quantizer 720 may quantize the parameters 718. The quantized parameters 724 may be provided to a parameter encoder 740, which may encode the parameters 718 (e.g., in the quantized version 724) in the bitstream 802 as side information 503. Thus, the side information 503 may also be present in at least some of the sound field parameters 729, 549, such as Ψ1, Ψ2, 1-Ψ1, 1-Ψ2, Ω1, Ω2, a1, a2..., and possibly also in the global diffuseness parameter Ψ, or other information regarding the global diffuseness of the audio signal. To save on metadata bitrate, Ω sThe quantization of can be automatically reduced to coarser steps for sectors with high diffusivity.

[0187] The input audio signal representation 702 may also be provided to an analysis filterbank unit 704a. Thus, a filtered version 729 of the input signal 702 in the filterbank domain (e.g., time-frequency tile) may be output by the analysis filterbank unit 704a. The version 729 of the input audio signal representation 702 may be the same as the version 706 output by the analysis filterbank 704a, but may otherwise be different.

[0188] The encoder 700b (audio signal representation encoding unit) of FIG. 10 may also include a downmix stage 1700b that downmixes the audio signal 702 to a compressed (downmixed) version 736. The downmix stage 1700b may be instantiated, for example, by a channel selector. Due to the input audio signal representation 702 (HOA signal) including multiple channels, the channel selector 1700b may simply select channels corresponding to the FOA version (or at least a lower-order version) of the HOA signal 702 (e.g., the selected channels may be multiple channels, e.g., they may be, for example, four channels in the case of FOA, or more channels). This essentially simple selection operation allows the audio signal 702 to be compressed, thus requiring fewer bits. However, most of the audio information is not lost, since it is reconstructed by the audio signal representation decoding unit (e.g., 500) via the side information 503. For example, the (downmixed, compressed) transport channel 736 may include, for example, four channels, fewer than the HOA signal 702. The transport channels 736, together with the side information 503, may constitute a compressed Ambisonic spatial audio signal representation. In particular, Figure 10 shows that an EVS (Extended Speech Signal) coder 738 may be present to convert the transport channels 736 into a coded version 739 of the transport channels 736.

[0189] 7 shows another example of an audio signal representation encoding unit 700. Here, components 704, 708, 704, 712, 716, and 720 (or at least some of them) may be essentially the same as in example 700b of FIG. 10. However, an analysis filter bank 704a (which may or may not be the same as analysis filter bank 704) may provide a filter bank domain version 729 of the input audio signal representation 702. The filter bank domain version 729 may be downmixed in a downmix stage 1700a. The downmix stage 1700a may include a downmix unit 730 (e.g., a downmixer or downmixer) to obtain a downmix version 732 (in the filter bank domain) of the HOA signal 702. The downmix version 732 may have a single transport channel or multiple transport channels, depending on the particular downmix performed. The downmix version 732 of the HOA signal 702 may be subjected to a synthesis filter bank 734 to obtain the transport channel 501 (e.g., a downmix compressed version 736 of the HOA signal 702 in the time domain). The synthesized version 736 (which may or may not be an FOA signal, but in either case in fewer channels than the original signal 702) of the downmix version 732 of the audio signal 702 (compressed transport channel) may then be provided as version 736 to one or more instances of an EVS coder 738 or any other mono audio coder. The transport channel 501 (736), for example, together with the side information 503, may be stored and / or transmitted to form a compressed version of the Ambisonic spatial audio signal representation 502. However, in particular, the compressed Ambisonic spatial audio signal representation 502 may comprise any of the compressed (downmix) versions 732, 736, 739 in addition to the side information 503.

[0190] The filtered input signal 729 may be downmixed and mixing or covariance information may be provided to an audio signal representation decoding unit (e.g., in at least one transport channel), although this is not the case in all instances. In some cases discussed below, the audio signal representation decoding unit (e.g., 500b, see below) can reconstruct mixing information even if covariance information is not written into the bitstream (coded signal) 802.

[0191] The filtered domain version 729 of the input audio signal representation 702 may be downmixed in a downmix unit 730 to obtain a downmix version 732. The downmix version 732 may be applied to a synthesis filter bank 734. A synthesized version 736 of the downmix version 732 of the audio signal 702 may then be provided to an EVS coder 738. The compressed transport channel 736 may then be encoded by the EVS coder 738, or one instance of any other mono audio coder in block 738, to obtain at least one encoded transport channel 739 (an encoded version of the compressed transport channel 736). The compressed transport channel 739 may be stored and / or transmitted, for example, together with the side information 503, to form the compressed version 502 (in the coded signal or bitstream 802) of the Ambisonic spatial audio signal representation 502.

[0192] It should be noted that the "compressed transport channels 736, 501" may or may not be instantiations of "at least one transport channel 501" of the "compressed Ambisonic spatial audio signal representation 502" (which may be decompressed, for example, in Fig. 5a). If the at least one transport channel 736 is compressed, it must be decompressed (upmixed) by an upmixing unit (550, see below in Fig. 5b) to recover the transport channel of the compressed Ambisonic spatial audio signal representation 502. The fact that it is further compressed improves efficiency.

[0193] The downmix matrix calculator 726 may provide a downmix matrix 728 to the downmix unit 730. The downmix matrix calculator 726 may utilize covariance information (e.g., a covariance matrix), described in more detail below, to perform inter-channel prediction. The downmix matrix calculator 726 may be more generally referred to as a "downmix information calculator," although for simplicity, "downmix matrix calculator" is preferred.

[0194] The version 732, 736, or 739 of the Ambisonic spatial audio signal representation 702 may be provided to a bitstream writer (multiplexer, encoded signal coder) (coded signal coder) 750 to provide the compressed Ambisonic spatial audio signal representation 502 (bitstream, coded signal) to an external device or storage unit (e.g., by transmission).

[0195] The downmix unit 730 may apply sound field parameters (sector diffuseness parameters, directivity parameters (529, 549, 718) that provide information about the direction of arrival (DoA) for each parameter, etc.) to perform the downmix. For this purpose, the downmix unit 730 may utilize a downmix matrix 728 that may be output by a downmix matrix calculator 726. The downmix matrix calculator 726 may obtain the downmix matrix 728 from a covariance matrix (or more generally, covariance information) estimated from the sound field parameters 718 or a quantized version thereof 722. As can be seen, in practice, the downmix matrix calculator 726 is shown to receive an input 722 that includes the sound field parameters 718 (e.g., in quantized form, but in other cases in unquantized form, e.g., 718 or 714, including, e.g., 7141, 7142, ..., 714n). The downmix matrix calculator 726 may or may not perform the same operations of the mixing matrix estimator 100 (in particular the covariance matrix combiner 102 and the mixing matrix builder 106 of Fig. 5b) discussed below on the decoder side. The downmix unit 730 may in principle be considered as corresponding to the upmix block 110 of Fig. 5b (although in the two cases the matrices do not correspond to each other).

[0196] We will now discuss the operation in the downmix matrix calculator 726. The downmix matrix (or more generally, downmix information) can be obtained from the covariance matrix (or more generally, covariance information). Therefore, we will first discuss how to obtain the covariance matrix (or covariance information). First, an inter-channel covariance matrix C can be defined. The inter-channel covariance matrix C is expressed as (L+1), where L is the order of the Ambisonic signal in version 501 to be input to decoder 500 (version 501c to be input to part 500 of decoder 500b, see below for FIG. 5b). 2 ×(L+1) 2 square matrix (i.e., (L+1) 2 Row and (L+1) 2(e.g., for FOA signals, L=1 and (L+1) 2 = 4 rows and (L+1) 2 = 4 columns). The covariance matrix (L+1) 2 Each of the rows and (L+1) 2 Each of the columns is arranged in a predefined order (L+1) such that the elements give the covariance between the Ambisonic channel corresponding to the row and the Ambisonic channel corresponding to the column. 2 corresponds to one of the Ambisonic channels, where the general matrix elements are C lm,l'm' For example, for an FOA signal, l is equal to 0 or 1, and m=0 when l=0, and m=-1, 0, +1 when l=1, which results in four combinations and a 4x4 covariance matrix. The covariance matrix may be a symmetric matrix. Each off-diagonal element of the covariance matrix provides covariance information between two Ambisonic channels. Generally speaking, the stronger the correlation between two Ambisonic channels, the higher the covariance in the corresponding matrix element, while the weaker the correlation between two Ambisonic channels, the lower the covariance in the corresponding matrix element. For the off-diagonal matrix elements, the element C lm,l'm' teeth,

[0197]

number

[0198] where E x is the signal energy, Ω1 and Ω2 are the first and second directivity parameters (e.g., sector DoA), respectively, and “a1” and “a2” are coefficients that indicate the relative directivity of the audio signal 702 in a particular sector relative to the directivity of the signal in the entire sector, as discussed above, for example.

[0199]

number

[0200] and

[0201]

number

[0202] Ψ is the global diffusivity parameter, and Y lm (Ω1), Y l'm' (Ω1), Y lm (Ω2), and Y l'm' (Ω2) is a spherical harmonic function evaluated for the DoA for each sector and each Ambisonic channel. This is valid for the case of two spatial sectors.

[0203] Since there is no covariance in the diagonal matrix elements (l=l', m=m'), the general diagonal matrix elements have the same meaning as the symbols, and are written as follows:

[0204]

number

[0205] where σ is a predetermined energy scaling factor.

[0206] A more concise expression is C lm,l'm' = (1-Ψ)*E x *a1 2 *Y lm (Ω1)*Y l'm' (Ω1)+ (1-Ψ)*E x *a2 2 *Y lm (Ω2)*Y l'm' (Ω2)+ +Ψ*σ2*E x *δ lm,l'm' where δ lm,l'm' is the Kronecker delta which is 1 on the diagonal of the inter-channel covariance matrix and 0 off the diagonal of the inter-channel covariance matrix.

[0207] The covariance matrix is 1) Off-diagonal element C mn,m'n' For each spatial sector in a. Non-global diffuse energy of the audio signal (1-Ψ)*E x and, b. spherical harmonics evaluated in the first DoAΩ1 and scaled by the relative directivity of the spatial sector to the sum of the directivities of the other spatial sectors; c. Spherical harmonics evaluated in the second DoA Ω2 and scaled by the relative directivity of the spatial sector to the sum of the directivities of the other spatial sectors; and the component obtained by multiplication between 2) Off-diagonal element C mn,mn In a. For each spatial sector: i. Non-global diffuse energy of the audio signal (1-Ψ)*E x and, ii.Directed energy for each sector

[0208]

number

[0209] (each

[0210]

number

[0211] )and and the component obtained by multiplication between b. A predefined scaling factor σ 2 The global diffusion energy Ψ*E x and a global component that scales may include:

[0212] Therefore, the inter-channel covariance matrix C (element C mn,m'n') is calculated in the downmix calculator 726 as Ω for all s. s , Ψ, Ψ s where s=1...n is the sector index.

[0213] This inter-channel covariance matrix in turn enables the downmix matrix and upmix matrix to be derived in the audio signal representation encoding unit and audio signal representation decoding unit, respectively. Thus, the step of encoding the covariance matrix in the bitstream 502 can advantageously be skipped. Specifically, the downmix matrix calculator 726 can be configured to perform inter-channel prediction (between Ambisonic channels). This prediction is based on the inter-channel covariance matrix 732 (derived from the directivity parameters and sector diffuseness parameters for each spatial sector and one or more parameters indicating the global diffuseness or the ratio or relationship between the diffuseness or diffuse energy of one sector and the diffuseness or diffuse energy of all sectors), and can achieve energy compression between the audio channels 729.

[0214] In the audio signal representation coding unit, the downmix matrix is ​​calculated using the FOA input signal, for example, by the formula

[0215]

number

[0216] via the covariance matrix C mn,m'n' To model uncorrelated signals using a decorrelator in the decoder, additional terms may or may not enter the matrix.

[0217] Reference is now made to an audio signal representation decoding unit 500b (Figure 5), which may comprise a portion 500 (which is identical to the audio signal representation decoding unit 500 of Figure 5a and is therefore denoted by the same reference number 500). In Figure 5b, the transport channel 501 is converted from a downmix compressed version 501b to an upmix version 501c (still compressed, but at least in the sense of an FOA version) and provided to the portion 500, thereby providing the transport channel 501. Thus, in the portion 500, the audio signal representation decoding unit 500b of Figure 5b operates in a similar manner to the audio signal representation decoding unit 500 of Figure 5a, to provide an uncompressed Ambisonic spatial audio signal representation 562.

[0218] In the audio signal representation decoding unit 500b (Fig. 5b), the mixing matrix reconstructor 106 (see below) calculates the upmix matrix (mixing matrix) 108 as the inverse of the downmix matrix, which may be calculated from the inter-channel covariance matrix 104. This may also occur by use of a predefined formula derived to generate the inverse of the downmix matrix 728.

[0219] More generally, the covariance information can be used to estimate the DoA (e.g., Ω_1..Ω N ) and the mixing weights a1..a for each spatial sector. N It can be based on.

[0220] More generally, instead of a covariance matrix, covariance information may be used, for example, together with global diffuseness information (eg, the global diffuseness parameter Ψ, or other information regarding the global diffuseness of the audio signal).

[0221] Figure 5b shows an example of an audio signal representation decoding unit 500b that generates an uncompressed Ambisonic spatial audio signal representation 562 from downmix transport channels 501 in a compressed Ambisonic spatial audio signal representation 502 that has been inserted into a bitstream 802 (coded signal), for example, by the audio signal representation encoding unit 700 of Figure 7. Here, at least one downmix transport channel 501 of the compressed Ambisonic spatial audio signal representation 502 may be an FOA compressed downmix version of the input audio signal 702.

[0222] 5b shows an example of an audio signal representation decoding unit 500b that also includes an upmixing unit 550 in addition to block 500 of FIG. 5a. The upmixing unit 550 may receive side information 503 (e.g., at least some of Ψ1, Ψ2, a1, a2, Ω1, Ω2...) and at least one transport channel 501b from a bitstream 802 (coded signal). The at least one transport channel 501b may be an example of at least one transport channel 501 corresponding to a transport channel 501 upstream of an EVS coder 738. However, in this case, the at least one transport channel 501b (501) is upmixed to provide more transport channels. The at least one transport channel 501b (501) may be received from the bitstream 802 as an encoded transport channel 739 and decoded by an EVS decoder 738b (if the encoder 700 does not have an EVS encoder 738, the EVS decoder 738b may be avoided). The upmix transport channel is therefore denoted 501c, which is also an example of a transport channel 501. However, in this case the upmix is ​​performed from the side information 503 (directivity parameters, sector spreading parameters and global spreading) already discussed above.

[0223] As can be seen in FIG. 5b, the covariance matrix synthesizer 102 may receive side information 503 including global diffuseness information related to the directivity parameters Ω1, Ω2, ..., second diffuseness parameters Ψ1, Ψ2, ... (or in the form of relative directivity a1, a2, etc.), and other information that allows for deriving the global diffuseness. Here, the covariance matrix synthesizer 102 may thus obtain an inter-channel covariance matrix 104 (see above). The inter-channel covariance matrix 104 may include information about the covariance between different Ambisonic channels. Alternatively, the covariance information may be derived. The covariance matrix may be estimated in the encoder 700 and will therefore not be repeated here.

[0224] Essentially, the inter-channel covariance matrix 104 is calculated as follows: lm,l'm' =(1-Ψ)*E x *a1 2 *Y lm (Ω1)*Y l'm' (Ω1)+(1-Ψ)*E x *a2 2 *Y lm (Ω2)*Y l'm' (Ω2)+Ψ*σ 2 *E x *δ lm,l'm' It can be obtained as:

[0225] The inter-channel covariance matrix 104 may then be provided to a mixing matrix reconstructor 106, which reconstructs a mixing matrix 108 according to the number of transport channels to be in version 501c of transport channel 501b. Once the mixing matrix 108 is obtained by the mixing matrix reconstructor 106, the upmixing block 110 may use the mixing matrix 108 and apply it to transport channel 501b to convert it into transport channel version 501c (501) (e.g., in a multiple channel representation as an FOA signal having four channels) to be provided to block 500 of Figure 5a. Sound field parameters 503 are also provided to block 500.

[0226] It should be noted that the technique of 500b may be skipped if either the inter-channel covariance matrix or the mixing matrix is ​​written into the bitstream 802 or obtained in another manner. The covariance matrix combiner 102 and the mixing matrix reconstructor 106 cooperate to form the mixing matrix estimator 100. In particular, other techniques may be used to obtain the mixing matrix.

[0227] The above operations may be performed for each band. Reference is made to Figure 5c (which shows a variant 500b' of Figure 5b). The audio signal representation decoding unit 500b' may comprise a band combiner 570. The band combiner 570 may combine the covariance-related information 104 (from the bitstream 802 and / or the covariance matrix synthesizer 102) so that for some bands, a portion 104a of the covariance information comes from the bitstream 802, and for other bands, other covariance information 104 comes from the covariance matrix synthesizer 102. However, it should be noted that some parameters (e.g., sound field parameters such as DoA and / or diffuseness parameters) may be the same for a group of bands. Furthermore, it is understood that the covariance information 104 in the bitstream 802 may directly include covariance matrix elements or any other representation derived therefrom. For example, prediction coefficients or decorrelator channel weights may be such representations. In general, different representations may be mixed.

[0228] The mixing matrix 108 may be reconstructed for each band (e.g., in example 500b of FIG. 5b). However, in some examples (e.g., in variant 500b' of FIG. 5c), for some bands, entries of the mixing matrix 108, or other parameters encoding covariance information or prediction information, may be coded in the side information 503, while for other bands, they are skipped. This is done in the band combiner unit 595, which provides the entries of the matrix 108 as 104a (e.g., in variant 500b' of FIG. 5c). Here, the sector directivity parameter and the sector spreading parameter (e.g., relative directivity) may be used to obtain the mixing matrix 108 via the covariance matrix only for some bands (e.g., high-frequency bands), while for other bands (e.g., lower-frequency bands), the entries of the mixing matrix 108 (or mixing information) may be written into the side information parameters 503. For example, a sound field model (ie, one that derives covariance from sound field parameters) can be used only in the high frequency bands, where inaccuracies have less perceptual impact.

[0229] In some examples (e.g., in an audio signal representation decoding unit) a low-order operation mode in which at least one sector decoding path (521, 541) among the plurality of sector decoding paths (521, 541) is deactivated, only one of the sector decoding paths (521, 541) is activated, and the side information (503) does not include sound field parameters (549) of the at least one deactivated sector decoding path (521, 541); a high-order operating mode in which all of the sector decoding paths (521, 541) are activated or at least fewer sector decoding paths are deactivated compared to the low-order operating mode, and the side information (503) includes sound field parameters (529, 549) of all of the sector decoding paths (521, 541) as well as global diffuseness parameters (507, 509); It should also be noted that it is possible to switch between

[0230] In some examples, the side information 503 may include a global diffuseness parameter even in a low-order mode of operation.

[0231] In some examples (e.g., in an audio signal representation coding unit, e.g., 700 or 700b) a low-order operating mode in which at least one sector path among the plurality of sector paths is deactivated and only one of the sector paths is activated, such that the side information does not include sound field parameters of the at least one deactivated sector path (global diffuseness parameters may also be encoded in the side information); a high-order operating mode, in which all of the multiple sector paths are activated or at least fewer sector paths are deactivated compared to the low-order operating mode, such that the side information includes sound field parameters of all of the multiple activated sector paths as well as a global diffuseness parameter; It should also be noted that it is possible to switch between

[0232] (In FIG. 7 or FIG. 10, the first sector path may include the series formed by blocks 7071, 7121 providing sector parameter set 1, 7141; the second sector may include the series formed by blocks 7072, 7122 providing sector parameter set 2, 7142; and the nth sector path may include the series formed by blocks 707n, 712n providing sector parameter set n, 714n, in the side information.)

[0233] For example, in an audio signal representation coding unit (e.g., 700 or 700b), in a low-order mode of operation, only sector parameter set 1 (7141) may be provided, while in a high-order mode of operation, both second parameters 1 and 2 (and possibly also n) are provided in the side information, and a global diffuseness parameter 7149 (507) may also be provided in the side information (in an example, the global diffuseness parameter may be provided in the side information in both the high-order and low-order modes of operation).

[0234] In some examples, the selection between the low-order operating mode and the high-order operating mode may be made by the audio signal representation encoding unit (e.g., 700 or 700b) and signaled in the side information 503 of the bitstream 802, and the audio signal representation decoding unit (e.g., 500, 500b, 500b') obtains the signaling in the side information 503 and then switches to the low-order operating mode or the high-order operating mode as appropriate under the control of the signaling.

[0235] Optionally, the selection between the low-order and high-order modes of operation may be static or may depend on the bit rate.

[0236] In some examples, the switching (e.g., selecting between a lower-order mode of operation and a higher-order mode of operation) is for only some bands, while in some other examples, the switching is for all bands.

[0237] Thus, a satisfactory trade-off can be achieved between keeping the bandwidth overhead low (by reducing the side information 503) and the most important bandwidth quality.

[0238] Optionally, the selection between the low-order and high-order modes of operation may be static or may depend on the bit rate.

[0239] For example, in a mobile communication scenario, the available bit rate may depend on the quality of the network connection, which may change over time. Thus, according to an example, the audio signal representation encoding unit (e.g., 700, 700b) and / or the audio signal representation decoding unit (e.g., 500, 500b, 500b') may dynamically switch between different bit rates. The audio signal representation encoding unit and / or the audio signal representation decoding unit may be configured to select a higher-order mode of operation at a high bit rate (e.g., a bit rate above a predetermined bit rate threshold) and / or to select a lower-order mode of operation at a low bit rate (e.g., the above-mentioned predetermined bit rate threshold) (the low bit rate is lower than the high bit rate). The quality may be measured, for example, from a measurement related to the quality of the network connection. (For example, quality may be measured via a latency measurement, such that a higher average latency for one or more messages results in lower quality and a lower average latency for one or more messages results in higher quality; in this case, the predetermined quality-related threshold is a latency threshold, such that a higher bit rate is selected for a lower average latency and a lower bit rate is selected for a higher average latency. Or quality may be measured via an error rate measurement based on checking the CRC fields of messages, such that a higher number of incorrect messages received results in lower quality and a lower number of incorrect messages received results in higher quality; in this case, the predetermined quality-related threshold may be an inaccurate message threshold (error rate threshold), such that a higher bit rate is selected for a number of incorrect messages below the inaccurate message threshold and a lower bit rate is selected for a number of incorrect messages above the inaccurate message threshold. Or quality may be measured via a connection bandwidth measurement, e.g., based on the average connection bandwidth; in this case, the predetermined quality-related threshold may be a bandwidth threshold, such that a higher bit rate is selected for a higher average bandwidth and a lower bit rate is selected for a lower average bandwidth.)) Measurements regarding the quality of a network connection may be obtained, for example, by cooperation between an audio signal representation encoding unit (e.g., a transmitter) and an audio signal representation decoding unit (e.g., a receiver). For example, an error rate may be measured by the audio signal representation decoding unit (receiver), and the value may be encoded and provided in feedback to the audio signal representation encoding unit. Also, latency may be measured by the audio signal representation encoding unit (e.g., a transmitter) when receiving a response to a specific pilot signal transmitted at a specific time and measuring the reception time of a specific response signal transmitted by the audio signal representation decoding unit (e.g., a receiver) in response to receiving the specific pilot signal. The latency may be calculated by subtracting the reception time of a specific response signal from the transmission time of the specific pilot signal. Another way for the audio signal representation encoding unit (e.g., a transmitter) to obtain latency may be, for example, by reading a timestamp in a message from the audio signal representation decoding unit (e.g., a receiver) to determine the latency of the message. Alternatively, a connection bandwidth measurement may be performed. Other quality-related measurements may also be performed. Thus, the selection between the high-order and low-order modes of operation may be based on a measurement of the quality of the network connection.

[0240] In an example, in an audio signal representation coding unit (e.g., 700, 700b), the bit rate may be selected, for example, by a user or by pre-selection (e.g., default pre-selection), or may be automatically selected depending on the quality of the network connection (e.g., lower quality corresponds to lower bit rates, and higher quality corresponds to higher bit rates). The audio signal representation coding unit may then select between a high-order mode of operation and a low-order mode of operation depending on the bit rate (e.g., a bit rate below a predetermined bit rate threshold indicates low quality and implies selection of the low-order mode of operation, and a bit rate above the predetermined bit rate threshold indicates higher quality than low quality and implies selection of the high-order mode of operation).

[0241] In an audio signal representation coding unit (e.g., 700, 700b), the selection of an operating mode between a low-order operating mode and a high-order operating mode may, for example, depend (partially or completely) on the input audio signal (e.g., completely or at least on the input audio signal). If a high-order input signal is available, the high-order operating mode may be selected. If only a low-order input signal is present, the audio signal representation coding unit may revert to the low-order operating mode.

[0242] In another example, an audio signal representation encoding unit (e.g., 700, 700b) may be configured to select a higher-order operating mode when a battery powering the audio signal representation encoding unit (e.g., a battery of a user equipment including the audio signal representation encoding unit) is fully charged (or at least charged above a predetermined charge threshold or battery supply threshold), and to select a lower-order operating mode when the battery is not fully charged (or at least charged below a predetermined charge threshold or battery supply threshold), e.g., when in a power saving mode.

[0243] The bit rate selected by the audio signal representation encoding unit (e.g., 700, 700b) is detected by the audio signal representation decoding unit (e.g., 500, 500b, 500b'). For example, the audio signal representation decoding unit (e.g., 500, 500b, 500b') may select a high-order mode of operation when a high bit rate (e.g., above a predetermined bit rate threshold) is received, and the audio signal representation decoding unit (e.g., 500, 500b, 500b') may select a low-order mode of operation when a lower bit rate (e.g., below a predetermined bit rate threshold) is received.

[0244] In another example, an audio signal representation decoding unit (e.g., 500, 500b, 500b') may select a high-order mode of operation if it is signaled in the bitstream (e.g., in the side information 503) that a high-order audio signal has been encoded by the audio signal representation encoder, and the audio signal representation decoding unit may select a low-order mode of operation if it is signaled in the bitstream (e.g., in 503) that a low-order audio signal has been encoded by the encoder.

[0245] In some other examples, the audio signal representation decoding unit (e.g., 500, 500b, 500b') may request a high bit rate from the network and select a high-order mode of operation, or the audio signal representation decoding unit may request a low bit rate from the network and select a low-order mode of operation. The bit rate selection may depend, for example, on a user setting (or a pre-selection, such as a default pre-selection) or the capabilities of the user equipment that includes the audio signal representation decoding unit.

[0246] In the above example, the sound field parameters may be changed to achieve a rotation of the sound field represented by the output Ambisonic signal (502). The DoA may include the direction from which the sound is coming. This is because, if it is necessary to achieve a rotation of the sound field (e.g., for head tracking), the audio signal representation decoding unit modifies those parameters to reduce the complexity of an additional rotation step. Thus, the audio signal representation decoding unit operates according to the parameter changes.

[0247] Below we provide some examples of the development of the audio signal representation 702 in FIG. In the audio signal representation coding unit 700, 1) The uncompressed audio signal representation 702 may be, for example, an HOA signal in the time domain, for example, having five or more channels; 2) In the downmix stage 1700a, a. In the filterbank analysis block 704a, the uncompressed audio signal representation 702 may be converted into a filterbank domain version 729; b. In the downmix unit 732, the filterbank domain version 729 may be converted into a downmix (compressed) version 732; c. After the filter bank synthesis block 734, the downmix (compressed) version 732 may be converted into a time-domain version 736 (in particular, the downmix version 732 may have a single transport channel or multiple transport channels); 3) In the EVS coder, the compressed downmix version 736 in the time domain can be converted into a coded version 739; 4) In the bitstream writer (eg, multiplexer) 750, the bitstream 802 is written.

[0248] Meanwhile, the HOA signal 702 can be processed to obtain sound field parameters 718, including sector directionality parameters and sector diffuseness parameters. From the sound field parameters 718, a covariance matrix and a downmix matrix 728 can be calculated to enable downmixing in 730. Additionally, a quantized representation of the sound field parameters is written into the bitstream (802) in a bitstream writer (multiplexer) (750).

[0249] In the apparatus 800 of FIG. 8 (including the audio signal representation decoding unit 500b of FIG. 5b or 500b′ of FIG. 5c), 1) The bitstream 802 is read by a bitstream reader and inverse quantizer 804 as a coded compressed Ambisonic spatial audio signal representation 502 (502b); 2) At least one coded transport channel 739 (501) is obtained from the bitstream 502 (502b); 3) In the EVS decoder 738b, at least one encoded transport channel 739 (501) is converted into at least one compressed and downmixed transport channel 501b (corresponding to transport channel 736 in FIG. 7); 4) In the upmixing block 110, at least one transport channel 501b is upmixed to transport channels 501c (501) (e.g., four FOA channels) via mixing information (e.g., mixing matrix) 108; 5) In part 500 of the audio signal representation decoding unit 500b (which corresponds completely to the audio signal representation decoding unit 500 of FIG. 5a), the four FOA channels 501 are split in a splitter block 504 between an FOA global diffuse signal 506 (in the global diffuse path 505) and an FOA global non-diffused signal 520; a. In the global diffuse path 505, the global diffuse signal 506 is subjected to a gain provided by the energy compensation block 508 to obtain an energy compensated global diffuse signal 510; b. In each of the sector decoding paths 521, 541, etc., the transport channel first unfolds through spatial filtering in a spatial filtering stage 574 and then through a sector signal processor 572 to obtain, for each spatial sector, a sector directional signal 532; 6) In a global diffuse signal inserter 560, the sector directional signals 532, 552 and the energy compensated global diffuse signal 510 are added together to derive an HOA-expanded Ambisonic spatial audio signal representation 562; 7) The HOA expanded Ambisonic spatial audio signal representation 562 can then be re-encoded as 816, or rendered as 814, or stored or transmitted as is.

[0250] As explained above, the inter-channel covariance matrix 104 and the mixing matrix 108 may be reconstructed from the sound field parameters in the side information to perform an upmix of at least one transport channel 501b to a transport channel 501(501c) to be fed to the portion 500 of the audio signal representation decoding unit 500b. The same sound field parameters are also used to process the transport channels in paths 505, 521, and 541 within the portion 500 of the audio signal representation decoding unit 500b.

[0251] Referring to the examples of the audio signal representation encoding unit 700b of Figure 10 and the audio signal representation decoding unit 500 of Figure 5a, they are generally similar, except that the downmix stage 1700a is performed by the channel section, no covariance matrix or downmix matrix is ​​calculated and / or reconstructed, and the transport channels 736 or 739 (e.g., four transport channels) are provided as transport channels 501 or directly to the audio signal representation decoding unit 500, and in particular to the divider 504.

[0252] In an example, the audio signal representation encoding unit (e.g., 700, 700b, etc.) may be or be integrated into a transmitter (e.g., transmitting via a geographical network and / or a local network, e.g., via wired or wireless or mixed transmission), and / or the audio signal representation decoding unit (e.g., 500, 500b, 500b', etc.) may be or be integrated into a receiver (e.g., receiving via a geographical network and / or a local network, e.g., via wired or wireless or mixed transmission).

[0253] Consider The present invention uses a combination of a first-order estimator and a high-order sector estimator for high-order directional audio coding (HO-DirAC).

[0254] In particular, we exploit a combination of both global and sectoral diffusivity to improve upon the state of the art shown in Figure 2 .

[0255] Note that the global diffuseness sets the balance between the directional and diffuse streams, and Ψ can be restored in the decoder (audio signal information decoding unit, e.g., 500, 500b, 500b′, etc.), which can receive Ψ from the bitstream or calculate it from the transport channel (501, 501c).

[0256] The decoder (audio signal information decoding unit, e.g., 500, 500b, 500b', etc.) in the directional stream derives the sector signal x from the transmitted FOA signal by beamforming (spatial / directional filtering), for example, according to the encoder sector design. s The sector signal can be extracted as follows: x s =w T s x L where w nm is the beamforming weight vector for sector s, and x L is the FOA signal vector. x s From the SH plane wave coefficients in the sector DoAΩ s By continuing in the direction of , the HOA signal is restored. x s =Y(Ω s )*x s =[x s Y 00 ,x s Y 1-1 ,x s Y 10 ,x s Y 11 ,...]

[0257] The sector (spatial sector) has a sector diffusivity ratio a sTherefore, the sector with less diffusion contributes more to the directional stream. The sector ratio can be, for example, for two sectors,

[0258]

number

[0259] , a2=1-a1, where Ψ s is the sector spreading estimated at the encoder.

[0260] The proposed design is flexible with respect to the number of sectors, the only constraint being Σ s x s =x 00 , Σ s a s = 1. This follows directly from the conservation of amplitude over the sector, as detailed in (References).

[0261] HOA signal vector x for one sector s H,s The restored directional part of x H,s =(1-Ψ)*a s *Y(Ω s )*x s is.

[0262] The diffuse part is rendered as a FOA signal vector and amplified by a gain factor that depends on the overall diffuseness and the input order L and output order H, as detailed in (reference),

[0263]

number

[0264] Summing over all HOA signal vectors and FOA signal vectors results in the decoder output HOA signal vector.

[0265] The proposed design with two DoA and higher-order sector processing according to Figure 5a can show significant improvements in a listening test (CICP19) over loudspeakers, the results of which are shown in Figure 6. In particular, items such as 4, which contain sound scenes with a wide spatial distribution of surrounding raindrops with distinct localizations, benefit significantly as the spatial impression tends to be corrupted by state-of-the-art methods, but this is improved by the proposed method. Other scenes tend to benefit or not degrade with the proposed method.

[0266] Furthermore, a more accurate multi-DoA model for directional signals is the inter-channel covariance matrix C x This allows for a more accurate estimation of C mn,m'n' =(1-Ψ)*E x *a1 2 *Y lm (Ω1)*Y l'm' (Ω1)+(1-Ψ)*E x *a2 2 *Y lm (Ω2)*Y l'm' (Ω2)++Ψ*σ 2 *Ex*δ lm,l'm' It could be.

[0267] This leads to more efficient compression of transport channels in current IVAS systems. In Figure 9a, 900 refers to the sector beams of one spatial sector. Panel 902 shows the four spherical harmonic functions belonging to the first channel (FOA) of the Ambisonic signal (e.g., 501). Panel 904 shows the filtered versions of these functions to which the sector beams from the first panel are applied. This can therefore be understood as the contribution of each FOA channel to the filtered signal (528) of this particular sector.

[0268] FIG. 9b shows the same but for two spatial sectors (eg, s=1 and s=2).

[0269] 9c shows the signal energy as a function of DoA. The input signal (top panel) 910 is a reference and corresponds to the audio signal 702 (or a version thereof) encoded by the audio signal representation encoding unit 700. Compared to an output signal 912 according to the prior art using a single DoA (e.g., corresponding to representation 262 in FIG. 2), the proposed method provides an output signal 914 (which may correspond to decoded representation 562 and / or its rendered version 814) whose energy distribution is more similar to the reference signal 702. Specifically, two independent sound sources in two directions are much more clearly separated, in contrast to 912, where a lot of energy leaks into the area between the actual sound sources.

[0270] In the diagram, the ordinate and abscissa refer to the zenith and azimuth coordinates. RMS means the root mean square of the signal energy.

[0271] Figure 9d displays the directivity and diffuseness parameters for four spatial sectors and the entire signal. A comparison between the upper and lower plots demonstrates that the sector-based method of the present invention can resolve different DoA and diffuseness values ​​for different sectors. In contrast, other methods with only one sector can only resolve one DoA and one diffuseness.

[0272] This disclosure also refers to an audio encoder comprising an audio signal representation encoding unit (e.g., of FIG. 7 or FIG. 10) and a quantizer and bitstream writer (e.g., element 40) that can write the compressed audio signal representation 502 into a bitstream.

[0273] Aspects: Some aspects will now be summarized. In comparison with the prior art: Sector processing, i.e., two or more DoAs and two or more diffuseness measures acting on the sector beamformer signal during reconstruction Differences from (References) Important novel aspects: A combination of overall diffusivity (e.g., from the first order) and sector diffusivity ratios (e.g., from higher orders) Differences from HOA coding, which is speaker rendering (references)

[0274] detail: 1 A device for parameterizing spatial audio scenes from High Order (HO) Spherical Harmonic Domain (SHD) signals, i.e. High Order Ambisonics (HOA). 1a. Transmitting a subset of the HOA input signal, e.g., but not limited to, First Order Ambisonics (FOA), and spatial parameterization as a set of metadata. 1b. Reconstructing untransmitted HOA signal components by utilizing transmitted metadata 1c Metadata containing two or more Directions of Arrival (DoA) 1d Combining a diffuseness estimate of the entire sound field estimated from first-order SHD with spatially localized diffuseness measures of two or more sound fields estimated from higher-order SHD 1e Psychoacoustic frequency weighting in group averaging of spatial parameterization 2. Device for reconstructing HOA signals using two or more DoAs and both global and spatially localized sound field diffuseness measurements 2a Re-estimation of primary parameters in the decoder (partial) 2b. To improve the performance of reconstruction based on parameters estimated from FOA, we utilize parameters estimated from HOA signals, thereby using both first-order and higher-order estimates. 3. Utilizing sector parameterization, e.g., but not limited to, two or more DoA, to predict HOA channel covariance (SPAR)

[0275] Further specifications Possible metadata (e.g. sound field parameters in side information 503) Possible comparison examples: Prior Art: DoA and Diffusivity: [Ω,Ψ](f) The technique: 2DoA, diffuseness (but can be estimated in the decoder 500) and sector diffuseness ratio (or more generally, sector diffuseness information such as relative directivity a1): [Ω1, Ω2, (Ψ), a](f)

[0276] In particular, it is possible to utilize currently used infrastructure and signal coders (bitstream writer 802) and is transparent to the decoder 500. Other important aspects: 1) Multi-DoA rendering using HO sectors (only the second set of DirAC parts needs to be sent and it is possible to use the same audio channel) 2) The direct energy of the proposed HO design has been confirmed to be equal to that of the conventional technology. 3) Sector signal reconstruction at the decoder depends on the FOA signal (preferable for higher bit rates) 4) Use an existing coder

[0277] Multi-DoA improves covariance prediction and reduces residual C R can be reduced C=C x +C R Currently:C x ~[x 00 Y(Ω)][...] T Suggestion:C x ~[a*x1*Y(Ω1)+(1-a)*x s2 *Y(Ω2)][...] T

[0278] Further implementations Depending on specific implementation requirements, examples may be implemented in hardware. Implementation may be performed using a digital storage medium, such as a floppy disk, digital versatile disk (DVD), Blu-ray disk, compact disk (CD), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory, on which electronically readable control signals are stored that cooperate (or can cooperate) with a programmable computer system to perform the respective methods. Thus, the digital storage medium may be computer-readable.

[0279] In general, the examples may be implemented as a computer program product having program instructions operable to perform one of the methods when the computer program product is executed on a computer. The program instructions may be stored on, for example, a machine-readable medium.

[0280] Other examples include the computer program for performing one of the methods described herein, stored on a machine-readable carrier. In other words, an example of a method is therefore a computer program having program instructions for performing one of the methods described herein, when the computer program runs on a computer.

[0281] A further example of a method is therefore a data carrier medium (or digital storage medium or computer readable medium) having recorded thereon a computer program for performing one of the methods described herein. The data carrier medium, digital storage medium or recorded medium is tangible and / or non-transitory rather than an intangible, transitory signal.

[0282] Further examples include a processing unit, for example a computer, or a programmable logic device, that performs one of the methods described herein.

[0283] A further example comprises a computer having installed thereon the computer program for performing one of the methods described herein.

[0284] Further examples include an apparatus or system that transfers (e.g., electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may be, for example, a computer, a mobile device, a memory device, etc. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver.

[0285] In some examples, a programmable logic device (e.g., a field programmable gate array) may be used to perform some or all of the functions of the methods described herein. In some examples, a field programmable gate array may cooperate with a microprocessor to perform one of the methods described herein. In general, the methods may be performed by any suitable hardware apparatus.

[0286] The examples described above are illustrative of the principles discussed above. It is understood that modifications and variations of the arrangements and details described herein will be apparent. It is therefore the intention to be limited only by the scope of the appended claims and not by the specific details presented by way of illustration and description of the examples herein. (References) [Explanation of symbols]

[0287] 40 elements 100 Mixing Matrix Estimator 102 Covariance matrix synthesizer 104 Inter-channel covariance matrix, covariance information, covariance-related information 104a Covariance information part 106 Mixing matrix constructor, Mixing matrix reconstructor 108 Upmix Functions, Mixing Matrices, Mixing Information 110 Upmixing Block 262 Expression 500 audio signal representation decoding unit, audio signal representation decoder unit, decoding unit, audio representation decoding unit, part, block, audio signal information decoding unit 500b Audio signal representation decoding unit, audio signal information decoding unit 500b' audio signal representation decoding unit, audio signal information decoding unit 500c Audio Signal Representation and Decoding Unit 501 transport channel, FOA transport channel, FOA signal, compressed transport channel, downmix transport channel, coded transport channel, Ambisonic signal 501b downmix compressed version, compressed ambisonic spatial audio signal representation, transport channel 501c upmix version, transport channel 502 Ambisonic spatial audio signal representation, audio signal representation, compressed Ambisonic spatial audio signal representation, FOA signal, low-order Ambisonic signal, input compressed Ambisonic spatial audio signal representation, FOA compressed version, encoded audio signal representation, bitstream, output Ambisonic signal, compressed audio signal representation 502b Compressed Ambisonic Spatial Audio Signal Representation 503 Side information, sound field parameters, side information parameters 504 Divider 505 Global Diffusive Signal Decoding Path, Path, Global Diffusive Path 506 Diffuse component, Diffuse signal, FOA global Diffuse signal, Global Diffuse signal 507 Global Diffusivity Parameters, Side Information 507' Global Diffusivity Parameters, Diffusivity, Side Information 508 Block, Energy Compensation Unit, Energy Compensation Block 509 Global Diffusivity Parameter 509' Diffusivity 510 Global Diffusive Signal, Global Diffusive, Energy Compensated Global Diffusive Signal 520 global non-spread signal, output 521 sector decryption route, route 522 Inputs, Paths, and Signals 524 Spatial Filtering Block, Block 526 Spatial Filtering Block, Block 528 Sector Signal, Sector Limited Version, Spatial Filtered Signal, Signal, Sector Signal Processor Block, Filtered Signal 529 sound field parameters, sector diffuseness parameters, directivity parameters, side information 530 block, sector signal processing block 532 directional sector signal, decoded directional sector signal, high-order directional sector signal, directional signal, sector signal, decoded sector signal, sector directional signal 541 Sector Decryption Path, Path 542 Input, Route 544 Spatial Filtering Block, Block 546 blocks 548 Sector signal, Sector limited version, Spatial filtered signal, Signal, Sector signal processor block, Directional signal 549 sound field parameters, sector diffuseness parameters, directivity parameters, side information 550 block, sector signal processing block, upmixing unit 552 directional sector signal, decoded directional sector signal, directional signal, sector signal, decoded sector signal, sector directional signal 555 High Order Directive Sector Signal 559 signal 560 Global Diffusive Signal Inserter 562 Expanded Ambisonic spatial audio signal representation, HOA signal, Expanded spatial audio signal representation, Compressed Ambisonic spatial audio signal representation, Expanded HOA version of audio signal, Audio signal, Audio signal Ambisonic spatial audio signal representation, Expanded HOA signal, HOA signal Ambisonic spatial audio signal representation, Decoded representation 570 Diffusion Estimator, Band Combiner 572 sector signal processor stage, stage sector signal processor, sector signal processor 574 Spatial Filtering Stage, Block 595 Band Combiner Unit 700 Audio signal representation encoding unit, encoding unit, audio signal representation decoding unit, encoder, unit 700b Audio signal representation coding unit, coding unit, Higher Order Ambisonic (HOA) audio signal representation coding unit, encoder 702 input spatial audio signal representation, audio signal, HOA signal, input audio signal representation, input signal, signal, input audio signal, audio signal representation, uncompressed audio signal representation, reference signal 704 Analysis Filter Bank 704a Analysis filter bank unit, analysis filter bank, filter bank analysis block 706 HOA signal version, filter bank domain version, filter bank domain HOA signal, HOA signal, version 708 spatial filter stage, spatial filtering stage 709 Global Diffusion Pathways 710 sector signal, spatially filtered Ambisonic expanded signal 710n sector signal 712 Sector Parameter Estimator 714 Sound Field Parameters, Parameters, First Representation 716 Parameter Converter Unit 718 sound field parameters, directional parameters, directional and diffuse parameters, second representation, parameters 720 Parameter Quantizer 721n Sector Parameter Estimator 722 quantized version, sound field parameters 724 quantized version 726 Downmix Matrix Calculator, Downmix Calculator 728 Downmix Matrix 729 sound field parameters, filtered version, version, filter bank domain version 730 Downmix Unit 732 downmix version, downmix compressed version, compressed (downmix) version, version, inter-channel covariance matrix, downmix unit, downmix (compressed) version 734 Synthesis Filter Bank, Filter Bank Synthesis Block 736 transport channel, version, compressed (downmix) version, composite version, compressed transport channel, compressed downmix version 738 EVS Coder, Block, EVS Encoder 738b EVS decoder 739 version, coded version, compressed (downmix) version, coded transport channel 740 Parameter Encoder 750 Bitstream Writer 800 equipment 802 Ambisonic spatial audio signal representation, audio signal representation, compressed Ambisonic spatial audio signal representation, bitstream, FOA compressed version 804 Inverse quantizer 812 Renderer 813 coding unit 814 Rendered Audio Signal, Audio Signal, Rendered Version 816 Transcoded Signal, Spatial Audio Signal Representation 900 Sector beam, panel 902 Panel 904 Panel 910 Input Signal 914 Output Signal 1700a Downmix Stage 1700b Downmix Stage 7071 Spatial Filter, Block 7072 Spatial Filter, Block 707n spatial filter, block 7101 Sector signal, signal 7102 Sector signal, signal 710n sector signal, signal Block 7121 7122 Block 712n Block 7129 Global Diffusivity Estimator 7141 Sound field parameters, values, parameters, sector parameter set 1 7142 Sound field parameters, values, parameters, sector parameter set 2 714n Sector Parameter Set n 7149 Global Diffusivity Parameter, Parameter 714n sound field parameters, values, parameters 7211 Sector Parameter Estimator 7212 Sector Parameter Estimator 721n Sector Parameter Estimator

Claims

1. an audio signal representation decoding unit (500) for generating an expanded Ambisonic spatial audio signal representation (562) from a compressed Ambisonic spatial audio signal representation (502) representing an audio signal, the compressed Ambisonic spatial audio signal representation (502) comprising at least one transport channel (501) and side information (503), the side information (503) comprising sound field parameters (529, 549, 718), the sound field parameters comprising, for each spatial sector of a plurality of spatial sectors, a directivity parameter (529, 549, 718) providing information on a direction of arrival (DoA) in the spatial sector, and the sound field parameters comprising, for at least one of the spatial sectors, a sector spreadness parameter (529, 549) providing information on a sector spreadness of the audio signal in the at least one spatial sector; the audio signal representation decoding unit includes a plurality of sector decoding paths (521, 541), each configured to decode a directional sector signal (532, 552) of the expanded Ambisonic spatial audio signal representation (562) in each spatial sector by applying the directivity parameter (529, 549) of the spatial sector and the sector spread parameter (529, 549) to the at least one transport channel (501) or a sector signal (528, 548) derived from the at least one transport channel; the audio signal representation decoding unit comprises a global diffuse signal decoding path (505) configured to derive a global diffuse signal (501) by applying a global diffuseness parameter (507, 507', Ψ) or other information related to the global diffuseness of the audio signal to the at least one transport channel (501); the audio signal representation decoding unit includes a global diffuse signal inserter (560) for combining the decoded directional sector signals (532, 552) and the global diffuse signal (510) to output the expanded Ambisonic spatial audio signal representation (562), An audio signal representation decoding unit (500).

2. 2. The audio signal representation decoding unit of claim 1, configured to apply the sector spread parameter (529, 549) to the at least one transport channel (501) or a sector signal derived from the transport channel (501) by weighting the transport channel (501) in at least one sector decoding path using a mixing weight derived from the sector spread parameter (529, 549), thereby deriving the directional sector signal (532, 552).

3. 3. The audio signal representation decoding unit of claim 2, configured to weight the at least one transport channel or a sector signal derived from the transport channel using the mixing weights that are positive coefficients received or processed from the sector diffuseness parameter or that are derived from the positive coefficients.

4. configured to weight, for at least one spatial sector, the at least one transport channel or a sector signal derived from the transport channel using the mixing weight; the blending weights are or are derived from coefficients indicative of sector directivity in the particular spatial sector; An audio signal representation decoding unit according to claim 2 or 3.

5. configured, for each spatial sector, to weight the at least one transport channel or a sector signal derived from the transport channel using the mixing weight; the mixing weights are or are derived from coefficients indicative of the relative directivity of the signal in a particular spatial sector relative to the relative directivity of the spatial sector as a whole; An audio signal representation decoding unit according to any one of claims 2 to 4.

6. configured, for at least one first spatial sector, to weight the at least one transport channel or a sector signal derived from the transport channel using a first mixing weight that is or is derived from a coefficient indicative of the sector directivity in the first spatial sector; and configured to weight the at least one transport channel or a sector signal derived from the transport channel using a second mixing weight for at least one second spatial sector; the audio signal representation decoding unit is configured to obtain the second mixing weights obtained by interpolating the coefficients indicating the sector directivity in the first spatial sector to a predetermined fixed value; An audio signal representation decoding unit according to any one of claims 2 to 5.

7. 7. The audio signal representation decoding unit of claim 2, configured to derive each of N-1 mixing weights from parameters described in the side information (503) and to derive an N-th mixing weight by complementing the other N-1 mixing weights to a constant positive value, where N is the number of spatial sectors.

8. In each sector decoding path, the DoA (Ω) in the spatial sector is calculated to extend the directional signal for the spatial sector to a higher Ambisonic order. s 8. The decoding unit according to claim 1, configured to apply the directivity parameter (529, 549) to at least one of the sector signals (528, 548) by multiplying the at least one sector signal by a vector of spherical harmonics evaluated along

9. 9. The decoding unit according to claim 1, configured to apply a spatial filter (574, 524, 544) to the at least one transport channel (520, 521) or a processed version of the at least one transport channel (520, 521) to limit the at least one transport channel (520, 521) to one spatial sector for each sector decoding path.

10. x s =x s *Y(Ω s )=[x s *Y 00 (Ω),x s *Y 1-1 (Ω),x s *Y 10 (Ω),x s *Y 11 (Ω),...] configured to calculate at least one directional sector signal (532, 552) using s is the transport channel or a processed version thereof in the particular spatial sector s, and Ω s is the directivity parameter of the particular spatial sector s, and Ω s If Y, which is a function of [Y 00 (Ω s ), Y 1-1 (Ω s ), Y 10 (Ω s ), Y 11 (Ω s ),...Y nm (Ω s ) and Y is the vector of spherical harmonics given by nm (Ω s 10. A decoding unit according to claim 1, wherein σ is a spherical harmonic function of order n and order m.

11. x H,s =(1-Ψ)*a s *Y(Ω s )*x s is configured to calculate at least one directional sector signal (532, 552) for at least a particular said spatial sector using, s is the sector spread parameter expressed as relative sector directivity in the at least one sector signal, and Y(Ω s ) is the DoAΩ in the particular spatial sector. s 11. A decoding unit according to claim 1, wherein σ is a vector of spherical harmonics evaluated along

12. 12. A decoding unit according to any one of claims 1 to 11, configured to read the global diffuseness parameter from the side information (507, 509).

13. 12. A decoding unit according to any one of claims 1 to 11, configured to estimate (570) the global spread parameter from the at least one transport channel (501).

14. applying said global diffuseness parameter (507, Ψ) or a global diffuseness weight obtained from said information on the global diffuseness of said audio signal to weight said at least one transport channel (501), thereby obtaining a global diffuseness signal version (506) to be used in said global diffuseness signal decoding path (505); configured to apply a second weight complementary to the global spreading weight to weight the at least one transport channel (501), thereby obtaining at least one global unspread signal (520) to be processed in the plurality of sector decoding paths (521, 541); A decoding unit according to any one of claims 1 to 13.

15. 15. The decoding unit according to claim 1, configured to derive mixing weights of the global diffuseness signal (510) and the directional sector signals (532, 552) from the global diffuseness parameter (507, 509, Ψ) or from the information on the global diffuseness of the audio signal.

16. 16. The decoding unit according to claim 1, configured to apply, for each sector decoding path, a weighting parameter to the at least one transport channel (501) that is complementary to the global spreading parameter used to derive the global spreading signal (510), such that the at least one transport channel is weighted using the weighting parameter.

17. the global diffuseness signal decoding path (505) is configured to weight the at least one transport channel (501) by a global diffuseness gain, which is or is derived from the global diffuseness parameter (507, Ψ) or the other information relating to the global diffuseness of the audio signal; each of the plurality of sector decoding paths (521, 541) is configured to weight the at least one transport channel (501) by a global directivity gain that is or is derived from the global diffuseness parameter (507) or the other information related to the global diffuseness of the audio signal; An audio signal representation decoding unit according to any one of claims 1 to 16.

18. the global diffuseness gain is 1+g(Ψ); [Equation 1] 18. The audio signal representation decoding unit of claim 17, wherein Ψ is or is derived from the global diffuseness parameter (507, 509) or the other information related to the global diffuseness of the audio signal, L is the Ambisonic input order, and H is the Ambisonic output order, according to

19. the global diffuseness gain is 1+g(Ψ); [Equation 2] where Ψ is or is derived from the global diffuseness parameter (507, 509) or the other information related to the global diffuseness of the audio signal, and f comp 18. An audio signal representation decoding unit according to claim 17, wherein: is a diffusion correction factor.

20. The diffusion correction coefficient is [Equation 3] where l is the order of the spherical harmonic function and L is the input signal (501, x L 20. The audio signal representation decoding unit of claim 19, wherein H is a higher Ambisonic order, or a signal comprising the transport channel and channels generated through the use of a decorrelator, and m is an index of spherical harmonics and takes values ​​from -l to l.

21. 21. An audio signal representation decoding unit according to any one of claims 17 to 20, wherein the range of values ​​of the global diffuseness gain is limited to a specific range of values ​​to prevent excessive deviation from the global diffuseness signal (506).

22. 22. An audio signal representation decoding unit according to any one of claims 17 to 21, wherein the global diffuse signal decoding path (505) comprises an energy compensation unit (508) that applies the gain to the global diffuse signal (506) to adjust the energy distribution in order to obtain a more physically realistic Ambisonics output signal (502).

23. a low-order operation mode in which, among the plurality of sector decoding paths (521, 541), at least one of the sector decoding paths (521, 541) is deactivated and only one of the sector decoding paths (521, 541) is activated, and the side information (503) does not include the sound field parameters (549) of the at least one deactivated sector decoding path (521, 541); a high-order operation mode in which, among the plurality of sector decoding paths (521, 541), all of the plurality of sector decoding paths (521, 541) are activated, or at least fewer sector decoding paths compared to the low-order operation mode are deactivated, and the side information (503) also includes the sound field parameters (529, 549) of all of the plurality of sector decoding paths (521, 541) and the global diffuseness parameters (507, 509); 23. An audio signal representation decoding unit according to any one of claims 1 to 22, configured to switch between

24. 24. An audio signal representation decoding unit according to any one of claims 1 to 23, configured to convert the spatial audio signal representation (502) from at least one encoded transport channel (739) into a decoded version of the at least one encoded transport channel (739).

25. 25. The audio signal representation decoding unit of claim 24, further comprising an EVS decoder (738b) that decodes the encoded at least one transport channel (739) into the decoded version of the encoded at least one transport channel (739).

26. 26. An audio signal representation decoding unit according to any one of claims 1 to 25, configured to transform the decoded Ambisonic spatial audio signal representation (562) from the filterbank domain to the time domain.

27. 27. The audio signal representation decoding unit of claim 1, further configured to upmix (110) the at least one transport channel (503) from a first number of transport channels (501b) to a second number of transport channels (501c), the second number being greater than the first number.

28. 28. The audio signal representation decoding unit according to claim 1, further comprising a mixing matrix estimator (106) configured to process the sound field parameters (503) to derive a covariance matrix (104) or other covariance information between different transport channels (501), the mixing matrix estimator (106) being configured to reconstruct a mixing matrix (108) or other mixing information from the covariance matrix (104) or the other covariance information and to apply the mixing matrix (108) or the other mixing information to the transport channels (501).

29. 29. The audio signal representation decoding unit of claim 28, wherein the covariance matrix synthesizer (102) is configured to process the sound field parameters including the DoA parameters and sector dispersity parameters of the multiple spatial sectors and the global diffuseness parameter or other information related to the global diffuseness to derive the covariance matrix (104) or the other covariance information between different transport channels, the mixing matrix estimator (106) is configured to reconstruct a mixing matrix (108) or the other mixing information from the covariance matrix (104) or the other covariance information to use the sound field parameters to derive the covariance matrix (104) or the other covariance information for at least one frequency band, and the audio signal representation decoding unit (500b) is configured to derive the covariance matrix (104) or the other covariance information for at least one other frequency band without using the sound field parameters.

30. 30. The audio signal representation decoding unit of claim 29, configured to derive the mixing matrix (104) or other mixing information from covariance information received from the side information (503) for at least one other frequency band.

31. An audio signal representation decoding unit (500) according to any one of claims 1 to 30, a bitstream reader and inverse quantizer (804) configured to read a bitstream (802) in which the encoded low-order spatial audio signal representation (502) resides and to provide the high-order spatial audio signal representation (502) to the audio signal representation decoding unit (500); An apparatus (800) comprising:

32. a renderer (812) for rendering the audio signal (814) from the Ambisonic spatial audio signal representation (562); 32. The apparatus of claim 31, further comprising:

33. 33. The apparatus of claim 31 or 32, further comprising an encoding unit (813) for encoding the high-dimensional spatial audio signal representation (562) into a second spatial audio signal representation (816).

34. an audio signal representation encoding unit for encoding an input spatial audio signal representation (702) representative of an audio signal into a compressed Ambisonic spatial audio signal representation (502, 802) representative of said audio signal, comprising: the audio signal representation encoding unit is configured to downmix (1700a, 1700b) the input spatial audio signal representation (702) to derive at least one transport channel (736, 739, 501); the audio signal representation coding unit is configured to derive side information (503), the side information (503) comprising sound field parameters (714, 718, 549, 529), the sound field parameters (714, 718, 549, 529) comprising, for each spatial sector of a plurality of spatial sectors, a directivity parameter providing information about a direction of arrival DoA in the spatial sector, the sound field parameters comprising a sector diffuseness parameter providing information about the diffuseness of the audio signal (702) in at least one spatial sector; the audio signal representation coding unit comprises a plurality of sector parameter estimators (712, 7211, 7212, 721n), each sector parameter estimator (712, 7211, 7212, 721n) configured to process a particular sector signal (710, 7101, 7102, 710n) of the input spatial audio signal representation (702) in a particular spatial sector among the plurality of spatial sectors to derive information about the directivity parameters and the diffuseness of the audio signal (702) in the at least one spatial sector; the audio signal representation encoding unit includes a bitstream writer (750) for encoding the at least one transport channel (736, 501) and the side information (503); Audio signal representation coding unit.

35. 35. An audio signal representation coding unit (700) as claimed in claim 34, further comprising a global diffuseness parameter estimator (7129) for estimating a global diffuseness parameter (7149, 507, Ψ) to be inserted (716) into the side information (718, 503).

36. 35. An audio signal representation coding unit (700) according to claim 34, configured to refrain from writing a global diffuseness parameter (7129) in the bitstream.

37. 37. An audio signal representation coding unit (700) according to any one of claims 34 to 36, further configured to estimate a relative directivity of each particular spatial sector with respect to the directivity of all said spatial sectors, and to write said coefficients, or information indicative of said relative directivity, as sector diffuseness parameters.

38. The relative directivity is respectively a 1 and a 2 and further configured to estimate the spatial sector as including at least one of the first and second spatial sectors denoted by [Equation 4] and, a 2 =1-a 1 and satisfy Ψ 1 is the sector diffuseness information of the first spatial sector or is obtained from it, and Ψ 2 is the sector diffuseness information of the second spatial sector or is obtained therefrom; 38. An audio signal representation coding unit according to claim 37. [Request Item 39] [Number 5] Here, Σ j a j =1 wherein i denotes an ith specific spatial sector, j denotes a jth general spatial sector among the plurality of spatial sectors, and Ψ i and Ψ j indicates the sector diffuseness information of the i-th specific spatial sector and each j-th general spatial sector; 38. An audio signal representation coding unit according to claim 37.

40. 40. The audio signal representation coding unit of claim 34, configured to perform (1700a) an active downmix (730) of the audio signal (702) or a processed version thereof (729) using a downmix matrix (728) or other downmix information calculated by a downmix information calculator (726), wherein the downmix information calculator (726) is configured to process the sound field parameters to derive the downmix matrix (728) or other downmix information based on the global and sector diffuseness parameters and directivity parameters for each spatial sector of the plurality of spatial sectors.

41. 41. The audio signal representation coding unit of claim 40, wherein the information matrix calculator (726) is configured to perform inter-channel prediction to derive the downmix matrix (728) or other downmix information based on an inter-channel covariance matrix or other inter-channel covariance information, the inter-channel covariance matrix or other inter-channel covariance information being derived from the directivity parameter and sector diffuseness parameter for each spatial sector of the plurality of sectors and a global diffuseness.

42. The inter-channel covariance matrix C is a matrix of elements C between the Ambisonic channels having orders and indices l and l′, respectively, and the Ambisonic channels having orders and indices l′ and m′, respectively. lm,l'm' and C lm,l'm' = (1-Ψ)*E x *a 2 *Y lm (Oh 1 )*Y l'm' (Oh 1 )+ (1-Ψ)*E x *(1-a) 2 *Y lm (Oh 2 )*Y l'm' (Oh 2 )+ +P*s 2 *E x *d lm,l'm' is defined as calculated according to E x is the signal energy, and δ lm,l'm' is the Kronecker delta that is one on the diagonal of the inter-channel covariance matrix and zero off the diagonal of the inter-channel covariance matrix, and Ω 1 and Ω 2 42. The audio signal representation coding unit of claim 41, wherein "a" denotes the global diffuseness parameter, and "σ" denotes the energy scaling factor.

43. The inter-channel covariance matrix or other inter-channel covariance information is calculated by dividing the DoA(Ω 1 , Ω 2 , ..., Ω N ) and the spherical harmonic weighted energy evaluated at the mixing weight (a 1 , a 2 , ..., a N 39. An audio signal representation coding unit according to claim 37 or 38, based on

44. further configured to transform the input spatial audio signal representation (702) into a filterbank domain to derive a filterbank version (729) of the input spatial audio signal representation (702); further configured to downmix the filterbank domain version (729) of the input spatial audio signal representation (706) to derive the at least one transport channel (732) in the filterbank domain; further configured to perform a filter bank synthesis (734) from the filter bank domain to the time domain of the at least one transport channel (732), An audio signal representation coding unit according to any one of claims 34 to 42.

45. 45. An audio signal representation coding unit according to claim 34, configured to downmix the input spatial audio signal representation (706) using a channel selector (1700b) to derive the at least one transport channel (736, 501) by selecting lower-order channels from higher-order channels of the input spatial audio signal representation (706).

46. 46. ​​The audio signal representation coding unit of claim 34, further configured to perform Enhanced Voice Services EVS coding to provide an EVS coded version (739) of said at least one transport channel (736, 501).

47. an audio signal representation coding unit according to any one of claims 34 to 46; a quantizer and a bitstream writer for writing the low-order spatial audio signal representation (502) and / or the compressed Ambisonic spatial audio signal representation (502) into a bitstream (802); An audio encoder (700) comprising:

48. 1. A method for decompressing an Ambisonic spatial audio signal representation (562) representing an audio signal, the compressed Ambisonic spatial audio signal representation (502) comprising at least one transport channel (501) and side information (503), the side information (503) comprising sound field parameters (529, 549, 718), the sound field parameters comprising, for each spatial sector of a plurality of spatial sectors, a directivity parameter (529, 549, 718) providing information about a direction of arrival (DoA) in the spatial sector, and the sound field parameters comprising, for at least one spatial sector, a sector spreadness parameter (529, 549) providing information about a sector spreadness of the audio signal in the at least one spatial sector; the method comprising a step of using a plurality of sector decoding paths (521, 541), each of which decodes a directional sector signal (532, 552) of the Ambisonic spatial audio signal representation (562) in each spatial sector by applying the directivity parameter (529, 549) of the spatial sector and the sector spread parameter (529, 549) to the at least one transport channel (501) or a sector signal (528, 548) derived from the transport channel; the method comprising the step of using a global diffuse signal decoding path (505) to derive a global diffuse signal (510) by applying a global diffuseness parameter (507, 507', Ψ) or other information related to the global diffuseness of the audio signal to the at least one transport channel (501), the method comprising the step of combining the decoded directional sector signals (532, 552) and the global diffuse signal (510) via a global diffuse signal inserter (560) to output the expanded Ambisonic spatial audio signal representation (562), method.

49. 1. A method for encoding an input spatial audio signal representation (706) representative of an audio signal into a compressed Ambisonic spatial audio signal representation (502, 802) representative of said audio signal, comprising: the method includes a step of deriving at least one transport channel (736, 501) and side information (503), the side information (503) including sound field parameters (714, 718, 549, 529), the sound field parameters (714, 718, 549, 529) including, for each spatial sector of a plurality of spatial sectors, a directivity parameter providing information about a direction of arrival (DoA) in the particular spatial sector, and the sound field parameters including a sector diffuseness parameter providing information about the diffuseness of the audio signal (702) in at least one spatial sector; the method comprising using a plurality of sector parameter estimators (712, 7211, 7212, 721n), each sector parameter estimator (712, 7211, 7212, 721n) processing a particular sector signal (710, 7101, 7102, 710n) of the input spatial audio signal representation (706) in a particular spatial sector of the plurality of spatial sectors to derive information about the directivity parameters and the diffuseness of the audio signal (702) in the at least one spatial sector; the method comprising using the at least one transport channel (736, 501) and the encoding of the side information (503) into a bitstream, method.

50. 50. A non-transitory storage unit storing instructions that, when executed by a processor, cause the processor to perform the method of claim 48 or 49.

51. A compressed Ambisonic audio signal representation (802) comprising at least one transport channel (501) and side information (503), wherein the side information (503) comprises sound field parameters (529, 549, 718), wherein the sound field parameters comprise, for each spatial sector of a plurality of spatial sectors, a directivity parameter (529, 549, 718) providing information regarding a direction of arrival DoA in the spatial sector, and wherein the sound field parameters comprise, for at least one spatial sector, a sector diffuseness parameter (529, 549) and a global diffuseness parameter (509, 7149) providing information regarding the sector diffuseness of the audio signal in the at least one spatial sector.

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