Method and apparatus for rendering an Ambisonics audio signal

Abstract

The present document describes a method (400) for rendering an Ambisonics signal using a loudspeaker arrangement including S loudspeakers. The method (400) includes converting (401) a set of N Ambisonics channel signals (111) into a set of unfiltered pre-rendered signals (211), where N>1 and S>1. The method (400) further includes performing near-field compensation (referred to as NFC) filtering (402) of M unfiltered pre-rendered signals (211) of the set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using the corresponding S loudspeakers.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to the following priority applications: U.S. Patent Application No. 63 / 330,687 (Docket No. D21151USP1), filed April 13, 2022, European Patent Application No. 22168180.2 (Docket No. D21151EP), filed April 13, 2022, and Indian Patent Application No. 202241005922 (Docket No. D21151IN), filed February 03, 2022.

[0002] Technical Field This paper concerns the efficient rendering of Ambisonics audio signals. [Background technology]

[0003] The sound or sound field in a listening environment of a listener located at a listening position may be described using an Ambisonics (audio) signal. An Ambisonics signal may be considered as a multi-channel audio signal, with each channel corresponding to a particular directional pattern of the sound field at the listener's listening position. An Ambisonics signal may be described using a three-dimensional (3D) Cartesian coordinate system, with the origin of the coordinate system corresponding to the listening position, with the x-axis pointing forward, the y-axis pointing left, and the z-axis pointing up.

[0004] By increasing the number of audio signals or channels and by increasing the number of corresponding directional patterns (and corresponding panning functions), the accuracy with which the sound field is described can be increased. As an example, a first-order Ambisonics signal has N=4 channels or waveforms, namely a W channel that indicates the omnidirectional component of the sound field, an X channel that describes the sound field with a dipole directional pattern corresponding to the x-axis, a Y channel that describes the sound field with a dipole directional pattern corresponding to the y-axis, and a Z channel that describes the sound field with a dipole directional pattern corresponding to the z-axis. A second-order Ambisonics signal has N=9 channels, including the four channels of a first-order Ambisonics signal (also called B-format) plus five additional channels for different directional patterns. In general, an nth-order Ambisonics signal has N=(n+1) 2 channels, which is the (n-1)th order Ambisonics signal plus [(n+1) 2 -n 2 ] additional channels. An nth order Ambisonics signal, for n>1, is sometimes called a higher order Ambisonics (HOA) signal.

[0005] The HOA signal may be used to describe a 3D sound field independent of the arrangement of speakers used to render the HOA signal. Exemplary arrangements of speakers include headphones, or one or more arrangements of speakers, or a virtual reality rendering environment. Thus, it may be beneficial to provide the HOA signal to an audio renderer to allow the audio renderer to flexibly adapt the rendering of the HOA signal to different arrangements of speakers. Summary of the Invention [Problem to be solved by the invention]

[0006] The present document addresses the technical problem of rendering Ambisonics audio signals in an efficient manner. This technical problem is solved by the independent claims. Preferred examples are given in the dependent claims. [Means for solving the problem]

[0007] According to a first aspect, a method for rendering an Ambisonics signal using a loudspeaker arrangement having S loudspeakers is described. The method includes converting a set of N Ambisonics channel signals into a set of unfiltered pre-rendered signals, where N>1 and S>1, and N may be different from S. Furthermore, the method includes performing near-field compensation (referred to as NFC) filtering of M unfiltered pre-rendered signals of said set of unfiltered pre-rendered signals to provide a set of S filtered loudspeaker channel signals for rendering with the corresponding S loudspeakers. M may depend on the number of loudspeakers S and the order n of a Higher Order Ambisonics (HOA) signal corresponding to the set of N Ambisonics channel signals. More specifically, M=S*(n+1-m1), where m1 is the number of Ambisonics channel modes from the order n of the HOA signal filtered by the all-pass NFC filter. If no all-pass NFC filter is used, m1=0. The set of N Ambisonics channel signals may be Higher Order Ambisonics (HOA) signals. Additionally or alternatively, N=(n+1) 2 where n is the order of the HOA signal, n>1. Furthermore, S may be greater than 2. In a specific example, S may be equal to 6 or 16.

[0008] In some embodiments, performing NFC filtering of M unfiltered pre-rendered signals of the set of unfiltered pre-rendered signals to provide a set of S filtered loudspeaker channel signals for rendering using corresponding S loudspeakers includes determining a set of M filtered pre-rendered signals from the M unfiltered pre-rendered signals of the set of unfiltered pre-rendered signals based on NFC coefficients. Specifically, this determining may include multiplying in the frequency domain each of the S unfiltered pre-rendered signals of the M unfiltered pre-rendered signals of the set of unfiltered pre-rendered signals with an NFC coefficient d(m) for each m, 0≦m≦n. Alternatively, this determining may include multiplying in the frequency domain each of the S unfiltered pre-rendered signals of the M unfiltered pre-rendered signals of the set of unfiltered pre-rendered signals with an NFC filter d(m) for each m, 0≦m≦n. m , m, n ...

[0009] In some embodiments, the method may further include determining whether (N-m0) is less than M, where m0≧0 and depends on the number of Ambisonics channel modes from order n of the HOA signal filtered by the all-pass NFC filter. m0 may be the number of Ambisonics channel indices corresponding to the number of Ambisonics channel modes filtered by the all-pass NFC filter. If no all-pass NFC filter is used, m0=0. Furthermore, performing near-field compensation (referred to as NFC) filtering of M unfiltered pre-rendered signals of said set of unfiltered pre-rendered signals to provide a set of S filtered loudspeaker channel signals for rendering with the corresponding S loudspeakers includes performing NFC filtering on the M unfiltered pre-rendered signals of said set of unfiltered pre-rendered signals if, and in particular only if, (N-m0)>M or (N-m0)≧M.

[0010] In some embodiments, before transforming the set of N Ambisonics channel signals into a set of unfiltered pre-rendered signals, the method may further include determining whether (N-m0) is less than M, where m0>0 and depends on the number of Ambisonics channel modes from the order n of the HOA signal filtered by the all-pass NFC filter. m0 may be the number of Ambisonics channel indices corresponding to the number of Ambisonics channel modes filtered by the all-pass NFC filter. If no all-pass NFC filter is used, m0=0. Depending on whether (N-m0) is less than M, perform NFC filtering of the M unfiltered pre-rendered signals of said set of unfiltered pre-rendered signals or reverse the order of transformation and NFC filtering. Specifically, if (N-m0)>M, NFC filtering may be performed on the M unfiltered pre-rendered signals of said set of unfiltered pre-rendered signals. Otherwise, the order of transformation and NFC filtering may be reversed. Reversing the order may be understood as performing NFC filtering on a set of N Ambisonics channel signals to generate a set of N filtered Ambisonics channel signals and using that set of N filtered Ambisonics channel signals to generate a set of S filtered loudspeaker channel signals. In other words, NFC filtering, if necessary, is performed on the HOA signals and the transformation is performed on the already filtered HOA signals.

[0011] In some embodiments, performing NFC filtering on M unfiltered pre-rendered signals of the set of unfiltered pre-rendered signals may include performing time-domain filtering using a digital finite impulse response filter or a digital infinite impulse response filter on each one of the M unfiltered pre-rendered signals individually.

[0012] In some embodiments, the method may further comprise determining a reference distance for the set of N Ambisonics channel signals, in particular based on the bitstream of the Ambisonics signals, and further comprising determining a filter, in particular a coefficient of the filter, for performing NFC filtering based on the reference distance.

[0013] In some embodiments, converting the set of N Ambisonics channel signals into a set of M unfiltered pre-rendered signals includes, for a given loudspeaker k, converting an Ambisonics signal matrix C representing a frame of the set of N Ambisonics channel signals into a set of M unfiltered pre-rendered signals, k For a given loudspeaker k, the renderer matrix R k Specifically, it is a (n+1) × N matrix.

[0014] According to a second aspect, a rendering device for rendering an Ambisonics signal using a loudspeaker arrangement comprising S loudspeakers is described, the rendering device being configured to perform the method of the first aspect and any optional embodiment referring to the first aspect.

[0015] According to a third aspect, a software program is described, the software program may be adapted for execution on a processor and for performing the method of the first aspect and any optional embodiments referring to the first aspect.

[0016] According to a fourth aspect, a storage medium is described, which may comprise a software program adapted for execution on a processor and for implementing the method of the first aspect and any optional embodiments referring to the first aspect.

[0017] According to a fifth aspect, a computer program product is described, the computer program product may include executable instructions for carrying out the method of the first aspect and any optional embodiments referred to in the first aspect.

[0018] According to a sixth aspect, a decoder configured to decode a bitstream representative of an Ambisonics signal rendered by a loudspeaker arrangement comprising S loudspeakers is described, the decoder comprising a rendering device according to the second aspect.

[0019] It should be noted that the methods, devices, and systems, including preferred embodiments thereof, as outlined in this patent application may be used independently or in combination with other methods, devices, and systems disclosed herein. Furthermore, all aspects of the methods, devices, and systems outlined in this patent application may be combined in any manner. In particular, the features of the claims may be combined with each other in any manner. [Brief description of the drawings]

[0020] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0021] [Figure 1] FIG. 2 illustrates an exemplary rendering device for rendering an Ambisonics audio signal.

[0022] [Figure 2a] 1 shows an example of a rendering device with modified NFC processing.

[0023] [Figure 2b] 13 illustrates an exemplary rendering device with flexible NFC processing before or after "Ambisonics-to-Loudspeaker" conversion.

[0024] [Diagram 3] 1 shows a flowchart of an exemplary method for rendering an Ambisonics audio signal.

[0025] [Figure 4] 1 shows a flowchart of an example method for performing NFC filtering on an unfiltered pre-rendered signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] As outlined above, this paper is concerned with the efficient rendering of Ambisonics, and in particular HOA signals, as used for example within the MPEG-H 3D Audio standard, a coding standard that supports channel-based, object-based and scene-based audio coding to provide an improved and immersive 3D sound experience.

[0027] MPEG-H 3D Audio Low Complexity Profile Decoders support all formats including channel-based audio, object-based audio, and scene-based audio via Higher Order Ambisonics (HOA). MPEG-H 3D Audio Low Complexity Profile Decoders compliant with ISO / IEC23008-3:2019 / AMD2:2020 also support MPEG-H 3D Audio Baseline Profile, which is a subset of MPEG-H 3D Audio Low Complexity Profile. ISO / IEC23008-3:2019 / AMD2:2020 is incorporated herein by reference. [Non-Patent Document 1] ISO / IEC23008-3:2019 / AMD2:2020

[0028] According to section 12.4.3.4 NFC processing (Near Field Compensation processing) of specification ISO / IEC 23008-3:2019(E) (incorporated by reference) and as shown in the Ambisonics (particularly HOA) renderer 100 of FIG. 1 , an NFC filtering block 110 may be used before the “HOA to Loudspeaker Conversion” block 120. In particular, the Ambisonics renderer 100 may be configured to receive N Ambisonics (particularly HOA) channel signals 111 from a decode block, said decode block being configured to generate said Ambisonics channel signals 111 from an encoded bitstream. In case of headphone rendering, the Ambisonics channel signals 111 may be provided to an “Ambisonics to Headphone Conversion (H2B)” block 130, which may be configured to perform a binaural rendering of the N Ambisonics channel signals 111. For loudspeaker rendering, the Ambisonics channel signals 111 may be provided to an "Ambisonics to Loudspeaker Transform" block 120, which is configured to generate S loudspeaker signals 114 for corresponding S loudspeakers of a loudspeaker arrangement based on the N Ambisonics channel signals 111. The loudspeaker signals 114 may be generated using an Ambisonics rendering matrix R 113, which may be determined based on the arrangement of the S loudspeakers.

[0029] The processing in the "HOA to Loudspeaker Conversion" block 120 may include matrix multiplication, in particular the matrix multiplication: P = R × C where R is the HOA renderer matrix 113, C is the matrix of HOA decoded output channels 111 (also referred to herein as Ambisonics channel signals), and P is the renderer output 114 (also referred to herein as loudspeaker channel signals), as shown below.

Number

[0030] The definitions of the variables L, S, and N are given in Table 1.

Table 1

[0031] The elements of the HOA rendering matrix 113 are r i,j For all 0 ≤ i < S and 0 ≤ j < N, they are typically scalar weights for a given speaker layout. Thus, the process of obtaining the final rendered output for a particular channel (i.e., the loudspeaker channel for a particular loudspeaker) is the sum of the weighted samples of the HOA channels c j, k for all 0 ≤ j < N and 0 ≤ k < L can be regarded as the weighted sum. That is, the elements p of the matrix P i,k for all 0 ≤ i < S and 0 ≤ k < L can be regarded as the weighted sum of c j,k for all 0 ≤ j < N. Here, the weights are the rows of the renderer matrix R.

[0032] As shown in FIG. 1, if it is determined within the determination block 101 that the ambisonics channel signal 111 should be applied with NFC processing, it can be submitted to the NFC processing within the NFC processing block 110 before rendering. The bitstream received from the corresponding ambisonics encoder can indicate whether NFC processing should be applied in a variable or flag "UsesNfc". Alternatively or additionally, the bitstream may indicate a variable "NfcReferenceDistance" that represents the reference distance at which the sound source and / or the loudspeaker was assumed to be located during encoding.

[0033] The decision block 101 may be configured to determine whether to apply the NFC process based on the variables "UsesNfc" and / or "NfcReferenceDistance". In particular, the NFC process may be applied only if the variable "UsesNfc" indicates that the NFC process should be used (e.g., with the value "1"). Also, the NFC process may be applied only if the variable "NfcReferenceDistance" is greater than or equal to the value r max This can only be applied if the max is the maximum distance at which the loudspeakers of the actual loudspeaker arrangement are located from the listener's position. The loudspeakers may, for example, be arranged on one or more circles around the listener's position.

[0034] If NFC processing is applied, the Ambisonics channel signals 111 may be filtered in an NFC processing block 110 to provide filtered channel signals 112. The filtered channel signals 112 may then be processed in a transformation block 120 to provide (filtered) loudspeaker channel signals 114. The Ambisonics channel signals C 111 may then be replaced by the corresponding filtered channel signals 112 in the matrix multiplication described above.

[0035] The NFC processing may include, and in particular may consist of, the application of digital filters, in particular Finite Impulse Response (FIR) and / or Infinite Impulse Response (IIR) filters, to the individual Ambisonics channel signals 111. The filter coefficients may be determined based on the variable "NfcReferenceDistance". For a given HOA order n, the filter coefficients may be the same for all Ambisonics channels corresponding to HOA "modes" m within the given HOA order n, where 0≦m≦n. Thus, for a given HOA order n, a total of (n+1) different NFC filter sets (corresponding to the number of HOA "modes") are used. The grouping of Ambisonics channels for different HOA orders from 1 to 6 is presented in Table 2. [Table 2]

[0036] The NFC processing block 110 may be configured to apply an NFC filter in the time domain. Further details regarding NFC processing are described in ISO / IEC 23008-3:2019I, in particular in section 12.4.3.4, which is incorporated herein by reference.

[0037] It can be shown that the filtering operations performed in the NFC processing block 110 and the matrix multiplication operations performed in the transformation block 120 can be reordered (without affecting the final result). As a result, an alternative setup 200 of the Ambisonics renderer 100 may be provided, as shown in FIG. 2a. In the setup 200, the conversion of the Ambisonics signals to loudspeaker signals is performed in two stages, where in a first stage 220, (n+1) sets of S unfiltered pre-rendered loudspeaker signals 211 are obtained from the Ambisonics channel signals 111. Parallel processing may be applied to obtain each of the (n+1) sets of S unfiltered pre-rendered loudspeaker signals. For each of the (n+1) sets of S unfiltered pre-rendered loudspeaker signals, the transformation is performed by a weighted sum of the Ambisonics channel signals 111. The weights used to process each set are taken from a subset of the rendering matrix R 113. For example, for each set m, 0≦m≦n, a subset R(m) of the rendering matrix R 113 may be multiplied with the matrix C 111 of the Ambisonics channel signals.

number

[0038] For example, the weights for the first set of S pre-rendered loudspeaker signals 211 (m=0) correspond to the first column of the rendering matrix R 113, and the weights for the second set of S unfiltered pre-rendered loudspeaker signals 211 (m=1) correspond to the matrices of the second, third and fourth columns of the rendering matrix R 113. This assignment is derived from the grouping as shown in Table 2, where it should be noted that for the first set, only one Ambisonics channel is involved, namely the first channel (0), and thus the first column of the rendering matrix R 113. On the other hand, for the second set, a group of three subsequent Ambisonics channels is involved, namely channels (1,2,3), and thus the next three columns of the rendering matrix R 113.

[0039] In a second stage, NFC filtering 210 is applied to the set or subset of pre-rendered loudspeaker signals 211. In particular, for each of the (n+1) sets or subsets of unfiltered pre-rendered S loudspeaker signals 211, NFC filtering is applied individually to provide the (n+1) sets or subsets of filtered pre-rendered S loudspeaker signals 213. For example, one of the (n+1) sets of filtered pre-rendered S loudspeaker signals 213 is calculated as follows:

number

[0040] The resulting (n+1) sets of S filtered pre-rendered loudspeaker signals 213 are summed in block 212 to obtain the corresponding loudspeaker channel signals 114. If only a subset of the (n+1) sets is filtered, then the subset and the remaining unfiltered signals are summed, i.e., the sum of the (n+1) signals for each loudspeaker S. For example, the loudspeaker channel signals 114 are calculated as follows:

number

[0041] In other words, in block 212, for each loudspeaker, the (n+1) signals corresponding to the same particular loudspeaker are summed to give a sum of S filtered and rendered loudspeaker signals 114. Notably, the loudspeaker channel signals 114 in Figure 2a are identical to the loudspeaker channel signals 114 in Figure 1.

[0042] If NFC processing is not required in this setup, a direct conversion to loudspeaker channel signals 114 can also be performed by processing the Ambisonics channel signals 111 with a rendering matrix R 113.

[0043] In the setup of FIG. 1, the NFC processing is applied to N ambisonics channel signals 111, while in the setup of FIG. 2a, the NFC processing is applied to S*(n + 1) signals. Thus, the setup of FIG. 2a is computationally more efficient than the setup of FIG. 1 when the following holds, i.e., S*(n + 1) < N, i.e., S < (n + 1) (in the case of a 3D setup). This paper mainly describes the 3D setup, but it should be noted that it can be easily extended to the 2D setup. Therefore, when, for example, a "global pass" NFC filter is applied to one of the modes, as is generally done for m = 0, the above conditions should be adjusted, for example, to S*n < N - 1. More generally, the condition can be expressed as S*(n + 1 - m1) < N - m0. Here, m1 is the number of ambisonics channel modes from the order n of the HOA signal filtered by the global pass NFC filter, and m0 is the number of ambisonics channel indices corresponding to the number m1 of ambisonics channel modes.

[0044] Table 3 shows the reduction of filtering operations achievable for various scenarios.

Table 3

[0045] Thus, the setup of FIG. 2a is efficient for a relatively common speaker layout with S = 6 speakers supported by the MPEG-H LC decoder at a relatively high ambisonics order n. Generally, the setup of FIG. 2a is more efficient when the number N of HOA channels is higher than the number S*(n + 1) of speakers in the target loudspeaker layout.

[0046] 2b shows an Ambisonics renderer 300 utilizing a decision unit 201 configured to change the order of the conversion and NFC processing depending on the number of Ambisonics channels N and the number of loudspeaker channels S. If S≧(n+1), the NFC processing (in block 110) may be performed before the conversion processing (in block 120). On the other hand, if S<(n+1), the NFC processing conversion (in block 210) may be performed after the processing (in block 220). As a result, a particularly efficient processing may be achieved, as shown in Table 4. [Table 4]

[0047] FIG. 3 shows a flowchart of an exemplary (computer-implemented) method 400 for rendering an Ambisonics audio signal using a loudspeaker arrangement including S loudspeakers. The Ambisonics audio signal may be provided in a bitstream. The method 400 may be performed by a decoder configured to decode the bitstream. In particular, the set of N Ambisonics channel signals 111 may be derived from the bitstream. The set of N Ambisonics channel signals 111 may be Higher Order Ambisonics (HOA) signals. The number N of the Ambisonics channel signals 111 may be N=(n+1) 2 where n is the order of the Ambisonics signal, e.g., n>1.

[0048] The method 400 may include converting (401) the N Ambisonics channel signals 111 into a set of unfiltered pre-rendered signals 211. For example, the size of the set of unfiltered pre-rendered signals 211 is equal to S*(n+1). Typically N>1, and typically S>1. In particular S>2, e.g. S=6 or S=16. Thus, the loudspeaker channel signals 114 may be derived from the HOA signals.

[0049] Transforming the set of N Ambisonics channel signals 111 into a set of unfiltered pre-rendered signals 211 may be and / or may be performed using a matrix multiplication of the Ambisonics signal matrix C (which represents a frame of the set of N Ambisonics channel signals 111) and the renderer matrix R(m) for each of the “modes” m, given the Ambisonics order n, where 0≦m≦n. For each “mode” m, the renderer matrix R(m) may be an S×N matrix filled with zeros except for the non-zero elements of a subset of the column vectors of the renderer matrix R. The indices of those column vectors are taken from Table 2. For example, for n=2, the non-zero elements of the renderer matrix R(m) for m=2 are the (5th, 6th, 7th, 8th, 9th) column vectors of the renderer matrix R. These correspond to the Ambisonics channel indices in the group (4,5,6,7,8) of Table 2. Note that the column vector index is simply the offset (+1) of the Ambisonics channel index, which are located at the same position in R(m). In a practical implementation, there is no need to build such a redundant matrix, and element-wise multiplication is sufficient to perform this operation.

[0050] Thus, the conversion from the HOA signal to the different loudspeaker channel signals can be performed by computing linear combinations of the different Ambisonics channel signals using different sets of weights (from the renderer matrix R).

[0051] Further, the method 400 includes performing (402) near-field compensation (NFC) filtering of M unfiltered pre-rendered signals 211 of the set of unfiltered pre-rendered signals 211. For example, M is equal to S*(n+1). An example of step 402 is shown in FIG.

[0052] FIG. 4 shows a flowchart of an exemplary (computer-implemented) method 500 for NFC filtering of a set of M unfiltered pre-rendered signals.

[0053] In step 501, a set of M filtered pre-rendered signals 213 is determined from the set of unfiltered pre-rendered signals 211 based on the NFC coefficients. In particular, the unfiltered pre-rendered signals 211 of the set of unfiltered pre-rendered signals 211 may be multiplied by corresponding NFC filter coefficients to provide the set of M filtered pre-rendered signals.

[0054] In step 502, for each loudspeaker, the filtered pre-rendered signals 213 corresponding to the loudspeaker are summed to provide a set of S filtered loudspeaker channel signals 114. The set of S filtered loudspeaker channel signals 114 may be rendered to the corresponding loudspeaker.

[0055] The method 400 may include providing the S filtered loudspeaker channel signals 114 to a corresponding S loudspeaker, respectively. Alternatively or additionally, the method 400 may include rendering the S filtered loudspeaker channel signals 114 with a corresponding S loudspeaker, respectively.

[0056] Performing NFC filtering on the set of unfiltered pre-rendered signals 211 may include performing time-domain filtering using a digital Finite Impulse Response (FIR) filter and / or a digital Infinite Impulse Response (IIR) filter individually on each of the M unfiltered pre-rendered signals 211. The filter for the NFC processing may be determined based on data provided in a bitstream related to the Ambisonics audio signal. In particular, the method 400 may include determining a reference distance of the set of N Ambisonics channel signals 111, in particular based on the bitstream of the Ambisonics signal. Furthermore, the method 400 may include determining a filter, in particular a coefficient of the filter, for performing the NFC processing based on the reference distance.

[0057] NFC processing may be used to compensate for the fact that loudspeakers located at a limited distance from the listener position do not emit ideal plane sound waves, and the sound field representations used for Ambisonics typically assume that the emitted sound waves are plane waves.

[0058] Thus, a method 400 is described for applying NFC processing to loudspeaker channel signals (as opposed to applying NFC processing to Ambisonics channel signals), which may lead to a substantial reduction in computational complexity without affecting perceptual quality.

[0059] The method may include determining whether the number S of loudspeakers is less than (and equal to) the number (n+1), where n is the HOA order. M may be S*(n+1). NFC filtering may be performed on the S*(n+1) unfiltered pre-rendered signals 211 if, and especially if, (n+1)>S or (n+1)≧S. As a result of this, computational complexity may be reduced.

[0060] Therefore, the method includes determining whether the number S of loudspeakers is less than (n + 1), where n is the HOA order. Depending on this, NFC filtering can be performed on either the S*(n + 1) unfiltered pre-rendered signals 211 or the set of N ambisonics channel signals 111. In particular, NFC filtering can be performed on the set of S*(n + 1) unfiltered pre-rendered signals 211 when (n + 1) < S. On the other hand, if (n + 1) < S, NFC filtering can be performed on the set of N ambisonics channel signals 111. In particular, when (n + 1) < S, method 400 can include performing NFC filtering on the set of N ambisonics channel signals 111 to generate a set of N filtered ambisonics channel signals 112 and converting the set of N filtered ambisonics channel signals 112 into S filtered loudspeaker channel signals 114. Thus, when (n + 1) < S, NFC filtering can be selectively performed before the "ambisonics to loudspeaker" conversion. As a result, the computational complexity can be significantly reduced in particular.

[0061] As a result, method 400 can perform NFC filtering flexibly before or after the "ambisonics to loudspeaker" conversion. By doing so, the computational complexity can be reduced.

[0062] This document describes methods and rendering devices that allow ambisonics, in particular HOA signals, to be rendered in a particularly efficient manner by a loudspeaker layout.

[0063] It should be noted that the description and drawings are merely illustrative of the principles of the proposed method and system. Those skilled in the art will be able to implement various configurations not explicitly described or shown herein, but which embody the principles of the present invention and fall within the spirit and scope of the present invention. Moreover, all examples and embodiments outlined herein are expressly intended to be primarily for illustrative purposes only, to aid the reader in understanding the principles of the proposed method and system. Moreover, all statements herein providing principles, aspects, and embodiments of the present invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0064] Various aspects of the present invention can be understood from the following enumerated example embodiments (EEE).

[0065] [EEE1] A method (400) for rendering an Ambisonics signal using a loudspeaker arrangement having S loudspeakers, the method (400) comprising: converting (401) a set of N Ambisonics channel signals (111) into a set of unfiltered pre-rendered signals (211), where N>1 and S>1; performing (402) near-field compensation (referred to as NFC) filtering of M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using a corresponding S loudspeaker, method. [EEE2] performing (402) NFC filtering of M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using a corresponding S loudspeaker; · from said set of M unfiltered pre-rendered signals, determining a set of M filtered pre-rendered signals based on the NFC coefficients; for each loudspeaker S, summing the filtered pre-rendered signal and the remaining unfiltered pre-rendered signal corresponding to the loudspeaker to provide the set of S filtered loudspeaker channel signals (114), The method described in EEE2. [EEE3] 3. The method according to claim 1 or 2, wherein M depends on the number S of loudspeakers and the order n of a Higher Order Ambisonics (HOA) signal corresponding to said set of N Ambisonics channel signals (111). [EEE4] M=S*(n+1-m1), where m1 is the number of Ambisonics channel modes from order n of the HOA signal filtered by the all-pass NFC filter; The method according to any one of EEE1 to 3. [EEE5] The method according to EEE4 when citing EEE2, wherein the filtered pre-rendered signals and the remaining unfiltered pre-rendered signals corresponding to the loudspeakers are numbers n+1-m1 and m1 signals, respectively. [EEE6] The method according to EEE4 or 5, wherein m1=0. [EEE7] determining a set of M filtered pre-rendered signals from said set of unfiltered pre-rendered signals based on NFC coefficients, multiplication in the frequency domain of each of the S unfiltered pre-rendered signals of the M unfiltered pre-rendered signals (211) of the set of unfiltered pre-rendered signals by an NFC coefficient d(m) for each m, where 0≦m≦n; or For each of the S unfiltered pre-rendered signals out of the M unfiltered pre-rendered signals (211) of the set of unfiltered pre-rendered signals, an NFC filter d m and a time domain convolution with, where 0≦m≦n. The method according to any one of EEE3 to 6 when referencing EEE2. [EEE8] The method (400), determining whether (N-m0) is less than M, where m0≧0 and depends on the number of Ambisonics channel modes from order n of the HOA signal filtered by the all-pass NFC filter; performing (402) near-field compensation (referred to as NFC) filtering of M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using a corresponding S loudspeaker; performing (402) NFC filtering on M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) if and only if (N-m0)>M or (N-m0)≧M, The method according to any one of EEE3 to 7. 〔EEE9〕 Before converting (401) a set of N ambisonics channel signals (111) into a set of unfiltered pre-rendered signals (211), the method (400) further · determining whether (N - m0) is less than M, where m0 ≥ 0 and depends on the number of ambisonics channel modes from the order n of the HOA signal filtered by the all-pass NFC filter; · depending thereon, performing NFC filtering (402) on M unfiltered pre-rendered signals of the set of unfiltered pre-rendered signals (211), or reversing the order of conversion and NFC filtering, The method according to any one of EEE3 to 8. 〔EEE10〕 · when (N - m0) > M, performing NFC filtering (402) on M unfiltered pre-rendered signals (211) of the set of unfiltered pre-rendered signals (211); · when (N - m0) < M, reversing the order of conversion and NFC filtering, The method according to EEE9. 〔EEE11〕 Reversing the order of conversion and NFC filtering means · performing NFC filtering on the set of N ambisonics channel signals (111) to generate a set of N filtered ambisonics channel signals (112); · converting the set of N filtered ambisonics channel signals into the set of S filtered loudspeaker channel signals (114). The method according to EEE9 or 10. 〔EEE12〕 The method according to any one of EEE8 to 12, wherein m0 is the number of Ambisonics channel indices corresponding to the number of Ambisonics channel modes filtered by the all-pass NFC filter. [EEE13] The method according to EEE12, wherein m0=0. [EEE14] The method of any one of EEE1 to EEE13, wherein performing NFC filtering (402) on M unfiltered pre-rendered signals (211) of the set of unfiltered pre-rendered signals (211) comprises performing time-domain filtering using a digital finite impulse response filter or a digital infinite impulse response filter on each one of the M unfiltered pre-rendered signals (211) individually. [EEE15] The method comprises: determining a reference distance for said set of N Ambisonics channel signals, in particular based on a bitstream of said Ambisonics signals; determining a filter, in particular a filter coefficient, for performing the NFC filtering based on the reference distance, The method according to any one of EEE1 to 14. [EEE16] said set of N Ambisonics channel signals (111) being Higher Order Ambisonics (HOA) signals; and / or N=(n+1) 2 where n is the order of the HOA signal, and n>1. The method according to any one of EEE1 to 15. [EEE17] S>2; and / or S=6; or S=16 The method of any one of EEE1 to 16, wherein [EEE18] Transforming (401) the set of N Ambisonics channel signals (111) into the set of M unfiltered pre-rendered signals comprises, for a given loudspeaker k, an Ambisonics signal matrix C representing a frame of the set of N Ambisonics channel signals (111) and a renderer matrix R k This can be done using matrix multiplication with The renderer matrix R for a given loudspeaker k k Specifically, it is a (n+1) × N matrix. The method according to any one of EEE1 to 17. [EEE19] A computer program product having instructions which, when executed by a computer, cause the computer to perform a method (400) according to any one of EEE1 to EEE18. [EEE20] A rendering device (100) for rendering an Ambisonics signal using a loudspeaker arrangement having S loudspeakers, the rendering device (100) comprising: converting (401) a set of N Ambisonics channel signals (111) into a set of unfiltered pre-rendered signals (211), where N>1 and S>1; performing near-field compensation (referred to as NFC) filtering (402) of M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using a corresponding S loudspeaker; Rendering device. [EEE21] A method (400) for rendering an Ambisonics signal using a loudspeaker arrangement having S loudspeakers, the method (400) comprising: a step (401) of converting a set of N Ambisonics channel signals (111) into a set of S unfiltered loudspeaker channel signals (214), where N>1 and S>1; performing near-field compensation (referred to as NFC) filtering (402) of said set of S unfiltered loudspeaker channel signals (214) to provide a set of S filtered loudspeaker channel signals (114) for rendering using the corresponding S loudspeakers; method. [EEE22] The method (400), determining whether the number N of Ambisonics channel signals (111) is greater than the number S of loudspeakers; performing (402) NFC filtering on said set of S unfiltered loudspeaker channel signals (214) if and only if N>S or N≧S; The method described in EEE21. [EEE23] The method (400), determining whether the number N of Ambisonics channel signals (111) is greater than the number S of loudspeakers; accordingly performing NFC filtering (402) on said set of S unfiltered loudspeaker channel signals (214) or performing NFC filtering on said set of N Ambisonics channel signals (111), The method according to claim EEE21 or 22. [EEE24] The method (400), · When N > S, perform NFC filtering on said set of S unfiltered loudspeaker channel signals (214); · When N < S, including performing NFC filtering on said set of N ambisonics channel signals (111), The method according to EEE23. 〔EEE25〕 When the method (400) is such that N < S, · Perform NFC filtering on said set of N ambisonics channel signals (111) to generate a set of N filtered ambisonics channel signals (112); · including converting said set of N filtered ambisonics channel signals (112) into said set of S filtered loudspeaker channel signals (114), The method according to any one of EEE23 to 25. 〔EEE26〕 Performing NFC filtering on said set of S unfiltered loudspeaker channel signals (214) includes, for each one of said S unfiltered loudspeaker channel signals (214), performing time domain filtering using a digital finite impulse response filter or a digital infinite impulse response filter individually, The method according to any one of EEE21 to 25. 〔EEE27〕 When the method is such that · determining a reference distance of said set of N ambisonics channel signals (111), in particular based on the bitstream of the ambisonics signals; and · determining a filter for performing NFC processing, in particular the coefficients of the filter, based on said reference distance, The method according to any one of EEE21 to 26. 〔EEE28〕 said set of N Ambisonics channel signals (111) being higher-order Ambisonics signals; and / or N=(n+1) 2 where n is the order of the Ambisonics signal, and n>1. The method according to any one of claims EEE21 to 27. [EEE29] S>2; and / or S=6; or S=16 The method of any one of EEE21 to 28, wherein [EEE30] Transforming (401) the set of N Ambisonics channel signals (111) into the set of S unfiltered loudspeaker channel signals comprises the steps of: converting the set of N Ambisonics channel signals (111) into the set of S unfiltered loudspeaker channel signals by using an Ambisonics signal matrix C representing a frame of the set of N Ambisonics channel signals (111) and a renderer matrix R k to give a loudspeaker signal matrix P representing a frame of said set of S unfiltered loudspeaker channel signals (214), The renderer matrix R is specifically an S×N matrix. The method according to any one of claims EEE21 to 29. [EEE31] The method (400), providing the S filtered loudspeaker channel signals (114) to corresponding S loudspeakers, respectively; and / or Rendering the S filtered loudspeaker channel signals (114) using the S corresponding loudspeakers respectively; The method according to any one of claims EEE21 to 30. [EEE32] A method (500) for rendering an Ambisonics signal using a loudspeaker arrangement having S loudspeakers, the method (500) comprising: performing joint synthesis and rendering (501) on the set of Ambisonics ambient signals (301) to determine a set of S ambient loudspeaker signals; performing joint synthesis and rendering (501) on the set of dominant sound signals (302) to determine a set of S dominant loudspeaker signals; combining (503) the set of S ambient loudspeaker signals with the set of S dominant loudspeaker signals to provide a set of S unfiltered loudspeaker channel signals (214), where S>1; performing near-field compensation (referred to as NFC) filtering (504) of said set of S unfiltered loudspeaker channel signals (214) to provide a set of S filtered loudspeaker channel signals (114) for rendering using the corresponding S loudspeakers; method. [EEE33] A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out a method (300, 400) according to any one of claims EEE21 to 32. [EEE34] A rendering device (100) for rendering an Ambisonics signal using a loudspeaker arrangement comprising S loudspeakers, the rendering device (100) comprising: converting a set of N Ambisonics channel signals (111) into a set of S unfiltered loudspeaker channel signals (214), where N>1 and S>1; performing near-field compensation (referred to as NFC) filtering of said set of S unfiltered loudspeaker channel signals (214) to provide a set of S filtered loudspeaker channel signals (114) for rendering using said corresponding S loudspeakers; is configured to run Rendering device. [EEE35] 1. A rendering device for rendering an Ambisonics signal using a loudspeaker arrangement comprising S loudspeakers, the rendering device comprising: performing joint synthesis and rendering (301) on a set of Ambisonics ambient signals to determine a set of S ambient loudspeaker signals; performing joint synthesis and rendering (302) on the set of dominant sound signals to determine a set of S dominant loudspeaker signals; combining (214) the set of S ambient loudspeaker signals and the set of S dominant loudspeaker signals to provide a set of S unfiltered loudspeaker channel signals, where S>1; performing near-field compensation (referred to as NFC) filtering of said set of S unfiltered loudspeaker channel signals (214) to provide a set of S filtered loudspeaker channel signals (114) for rendering using said corresponding S loudspeakers; A rendering device that is configured to run [EEE36] A decoder (300) configured to decode a bitstream representative of an Ambisonics signal rendered by a loudspeaker arrangement comprising S loudspeakers, the decoder (300) comprising a rendering device (100) according to any one of claims EEE34 to EEE35.

Claims

1. 1. A method (400) for rendering an Ambisonics signal using a loudspeaker arrangement having S loudspeakers, the method (400) comprising: - converting (401) a set of N Ambisonics channel signals (111) into a set of unfiltered pre-rendered signals (211), where N>1 and S>1; performing near-field compensation (referred to as NFC) filtering (402) of M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using a corresponding S loudspeaker; method.

2. performing (402) NFC filtering of M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using a corresponding S loudspeaker; - determining, from said set of M unfiltered pre-rendered signals, a set of M filtered pre-rendered signals based on NFC coefficients; for each loudspeaker S, summing the filtered pre-rendered signal and the remaining unfiltered pre-rendered signal corresponding to the loudspeaker to provide the set of S filtered loudspeaker channel signals (114); The method of claim 1.

3. 2. The method of claim 1, wherein M depends on a number S of loudspeakers and an order n of a Higher Order Ambisonics (HOA) signal corresponding to said set of N Ambisonics channel signals (111).

4. M = S*(n+1-m 1 ), and m 1 is the number of Ambisonics channel modes from order n of the HOA signal filtered by the all-pass NFC filter; The method of claim 1.

5. M = S*(n+1-m 1 ), and m 1 is the number of Ambisonics channel modes from order n of the HOA signal filtered by the all-pass NFC filter, The filtered pre-rendered signal and the remaining unfiltered pre-rendered signal corresponding to the loudspeakers are each a number n+1−m 1 and m 1 The signals are The method of claim 2.

6. m 1 5. The method of claim 4, wherein: =0.

7. M depends on the number S of loudspeakers and the order n of a Higher Order Ambisonics (HOA) signal corresponding to said set of N Ambisonics channel signals (111); Determining a set of M filtered pre-rendered signals from said set of M unfiltered pre-rendered signals based on NFC coefficients includes: - multiplication in the frequency domain of each of the S unfiltered pre-rendered signals of the M unfiltered pre-rendered signals (211) of the set of unfiltered pre-rendered signals by an NFC coefficient d(m) for each m, where 0≦m≦n; or For each of the S unfiltered pre-rendered signals out of the M unfiltered pre-rendered signals (211) of the set of unfiltered pre-rendered signals, an NFC filter d m and a time domain convolution with, where 0≦m≦n. The method of claim 2.

8. The method (400), ・(N-m 0 ) is less than M, where m 0 ≧0 and depends on the number of Ambisonics channel modes from order n of the HOA signal filtered by the all-pass NFC filter; performing (402) near-field compensation (referred to as NFC) filtering of M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using a corresponding S loudspeaker; ・(N-m 0 )>M or (N-m 0 performing (402) NFC filtering on M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) if and only if M > M, The method according to claim 3.

9. Prior to converting (401) the set of N Ambisonics channel signals (111) into a set of unfiltered pre-rendered signals (211), the method (400) further comprises: ・(N-m 0 ) is less than M, where m 0 ≧0 and depends on the number of Ambisonics channel modes from order n of the HOA signal filtered by the all-pass NFC filter; performing (402) NFC filtering on M unfiltered pre-rendered signals of said set of unfiltered pre-rendered signals (211) depending thereon, or reversing the order of transformation and NFC filtering, The method according to claim 3.

10. ・(N-m 0 )>M, performing (402) NFC filtering on M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211); ・(N-m 0 ) < M, then reverse the order of conversion and NFC filtering; 10. The method of claim 9.

11. Reversing the order of conversion and NFC filtering performing NFC filtering on said set of N Ambisonics channel signals (111) to generate a set of N filtered Ambisonics channel signals (112); converting the set of N filtered Ambisonics channel signals into the set of S filtered loudspeaker channel signals (114), 10. The method of claim 9.

12. m 0 9. The method of claim 8, wherein x is the number of Ambisonics channel indices corresponding to the number of Ambisonics channel modes filtered by the all-pass NFC filter.

13. m 0 13. The method of claim 12, wherein: = 0.

14. 2. The method of claim 1, wherein performing NFC filtering (402) on M unfiltered pre-rendered signals (211) of the set of unfiltered pre-rendered signals (211) comprises performing time-domain filtering using a digital finite impulse response filter or a digital infinite impulse response filter on each one of the M unfiltered pre-rendered signals (211) individually.

15. The method comprises: determining a reference distance for said set of N Ambisonics channel signals, in particular based on a bitstream of said Ambisonics signals; determining a filter, in particular the coefficients of the filter, for performing the NFC filtering based on the reference distance, The method of claim 1.

16. said set of N Ambisonics channel signals (111) are Higher Order Ambisonics (HOA) signals; and / or ・N=(n+1) 2 where n is the order of the HOA signal, and n>1. The method of claim 1.

17. S>2; and / or S=6; or ・S＝16 The method of claim 1, wherein

18. Transforming (401) the set of N Ambisonics channel signals (111) into the set of M unfiltered pre-rendered signals comprises, for a given loudspeaker k, an Ambisonics signal matrix C representing a frame of the set of N Ambisonics channel signals (111) and a renderer matrix R k This can be done using matrix multiplication with The renderer matrix R for a given loudspeaker k k Specifically, it is a (n+1) × N matrix. The method of claim 1.

19. A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out a method (400) according to any one of claims 1 to 18.

20. A rendering device (100) for rendering an Ambisonics signal using a loudspeaker arrangement having S loudspeakers, the rendering device (100) comprising: - converting (401) a set of N Ambisonics channel signals (111) into a set of unfiltered pre-rendered signals (211), where N>1 and S>1; performing near-field compensation (referred to as NFC) filtering (402) of M unfiltered pre-rendered signals (211) of said set of unfiltered pre-rendered signals (211) to provide a set of S filtered loudspeaker channel signals (114) for rendering using a corresponding S loudspeaker; Rendering device.

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