Apparatus, method and computer program for enabling spatial audio rendering - Patents.com

Abstract

An example of the present disclosure enables rendering of spatial audio in a format different from the format used to code the spatial audio. In an example of the present disclosure, spatial audio and first spatial metadata are obtained in a first format. The first spatial metadata enables rendering of the spatial audio in the first audio format. To enable rendering of the spatial audio in the different format, the spatial metadata is converted to second spatial metadata corresponding to the second audio format. The spatial audio can then be rendered for the second format using the second spatial metadata.

Description

[Technical field]

[0001] Examples of the present disclosure relate to an apparatus, method, and computer program for enabling rendering of spatial audio, in part, to an apparatus, method, and computer program for enabling rendering of spatial audio in different audio formats. [Background technology]

[0002] Spatial audio allows the spatial properties of a sound scene to be reproduced for a user so that the user can perceive the spatial properties, which can create an immersive audio experience for the user, or can be used for other purposes. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Vilkamo, J., Backstrom, T., Kuntz, A (2013), Optimized covariance domain framework for time-frequency processing of spatial audio, Journal of the Audio Engineering Society, 61(6), pp. 403-411. Summary of the Invention [Means for solving the problem]

[0004] According to various, but not necessarily all, examples of the present disclosure, an apparatus comprising: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; Enable rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals. An apparatus is provided that includes means for:

[0005] Determining the second spatial metadata using the first spatial metadata may include determining rendering information from the first spatial metadata and calculating the second spatial metadata from the rendering information.

[0006] The rendering information may include one or more mixing matrices.

[0007] Determining the second spatial metadata using the first spatial metadata may include directly calculating the second spatial metadata from the first spatial metadata.

[0008] Determining the second spatial metadata using the first spatial metadata may be based on one or more audio signals.

[0009] Determining the second spatial metadata using the first spatial metadata may include determining one or more covariance matrices of the one or more audio signals.

[0010] The means may be for determining the second spatial metadata without rendering the spatial audio in the first audio format.

[0011] Means may be for allowing different types of spatial metadata to be used to render different frequencies of the spatial audio.

[0012] General spatial metadata may be used to render a first set of frequencies of spatial audio, and further format-specific spatial metadata may be used for a second set of frequencies.

[0013] The audio formats may include one or more of: ambisonic formats, binaural formats, multi-channel loudspeaker formats.

[0014] The spatial metadata may include information that enables mixing of audio signals to enable rendering of spatial audio in a selected audio format.

[0015] The spatial metadata is for one or more frequency subbands; Sound direction, and Sound Directivity The information may include information indicating:

[0016] The spatial metadata may include one or more prediction coefficients for one or more frequency subbands.

[0017] The spatial metadata may include one or more coherence parameters.

[0018] According to various, but not necessarily all, examples of the present disclosure, an apparatus includes at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured by the at least one processor to cause the apparatus to perform at least: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; Enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals. An apparatus configured to:

[0019] According to various, but not necessarily all, examples of the present disclosure, there is provided an electronic device including an apparatus as described herein, the electronic device being at least one of: a telephone, a camera, a computing device, and a teleconferencing device.

[0020] According to various, but not necessarily all, examples of the present disclosure, a method includes: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals; A method is provided that includes:

[0021] According to various, but not necessarily all, examples of the present disclosure, a computer program comprising computer program instructions that, when executed by a processing circuit, perform: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals; A computer program is provided to cause the

[0022] Some examples will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram of an example system. [Diagram 2] FIG. [Diagram 3] FIG. 2 is a diagram of an example decoder. [Figure 4] FIG. 2 is a diagram of an example spatial synthesizer. [Diagram 5] FIG. 13 is a diagram of another example decoder. [Figure 6] FIG. 2 is a diagram of an example device. [Figure 7] FIG. 1 is a diagram of an exemplary apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Examples of the present disclosure enable rendering of spatial audio in a format different from the format used to code the spatial audio. In examples of the present disclosure, spatial audio and first spatial metadata are obtained in a first format. The first spatial metadata enables rendering of the spatial audio in the first audio format. To enable rendering of the spatial audio in the different format, the spatial metadata is converted to second spatial metadata corresponding to the second audio format. The spatial audio may then be rendered for the second format using the second spatial metadata.

[0025] 1 illustrates an example system 101 that can be used to implement examples of the present disclosure. The system includes an encoder 105 and a decoder 109. The encoder 105 and the decoder 109 may be in different devices. In some examples, the encoder 105 and the decoder 109 may be in the same device.

[0026] The system 101 is configured such that the encoder 105 obtains an input including an audio signal 103. In this example, the audio signal 103 may be a first order Ambisonic (FOA) signal. Other types of audio signals 103 may be used in other examples of this disclosure.

[0027] The audio signal 103 may be obtained from two or more microphones configured to capture spatial audio. In examples where the audio signal 103 includes an FOA audio signal, the FOA audio signal may be obtained from a dedicated Ambisonics microphone, such as an Eigenmike, or other suitable means.

[0028] The encoder 105 may comprise any means that may be configured to encode the audio signal 103 to provide a bitstream 107 as an output. The encoder 105 may be configured to encode the audio signal 103 using a parametric method. The parametric method may include an Immersive Voice and Audio Services (IVAS) method, or other suitable types of methods. The encoder 105 may be configured to determine a transport audio signal and spatial metadata using the audio signal 103. The transport audio signal and spatial metadata may then be multiplexed to provide the bitstream 107.

[0029] In some examples, the bitstream 107 may be transmitted from a device including the encoder 105 to a device including the encoder 109. In some examples, the bitstream 107 may be stored in a device including the encoder 105 and retrieved and decoded by the decoder 109 at any time.

[0030] The decoder 109 is configured to receive the bitstream 107 as an input. The decoder 109 comprises means that can be configured to decode the bitstream 107. The decoder 109 can decode the bitstream into transport audio and spatial metadata. The decoder 109 can be configured to render a spatial audio output 111 using the decoded spatial metadata.

[0031] If the system 101 is used to provide a spatial audio output 111 in the same format as that used for the spatial audio signal 103, the decoder 109 can use the spatial metadata provided in the bitstream 107 to render the spatial audio output 111.

[0032] In examples of the present disclosure, the system 101 may be configured to provide spatial audio output 111 in a format different from the format used for the spatial audio signal 103. In such examples, the decoder 109 may be configured to obtain a set of spatial metadata different from the spatial metadata provided in the bitstream 107. This different set of spatial metadata may enable the spatial audio output 111 to be rendered in a different format. For example, in the example of FIG. 1, the system may obtain a FOA audio signal. The decoder 109 may be configured to convert the spatial metadata in the bitstream 107 from FOA-related spatial metadata to binaural-related spatial metadata or other suitable type of spatial metadata.

[0033] 2-5 illustrate example methods and portions of a system 101 that can be used to enable different sets of spatial metadata to be obtained.

[0034] 2 illustrates an example method that can be used to enable rendering of spatial audio in different audio formats. The method can be implemented in a system 101, such as the system 101 illustrated in FIG.

[0035] The method includes, at block 201, obtaining an encoded spatial audio signal. The encoded spatial audio signal includes one or more audio signals and further includes first spatial metadata. The first spatial metadata is configured to enable rendering of spatial audio in a first audio format from the one or more audio signals. The first spatial metadata includes format-specific spatial metadata.

[0036] The first spatial metadata may include information indicative of one or more parameters specific to the first audio format for one or more frequency subbands. For example, if the first audio format is a FOA signal, the first spatial metadata may include information indicative of how to predict the FOA signal from the transport audio signal for one or more frequency subbands. Such information may include prediction coefficients for predicting the FOA signal from the transport audio signal. For example, an omnidirectional signal W of the FOA may be used as the transport audio signal, and the prediction coefficients may be used to predict the dipole signals X, Y, Z from the transmitted signal W.

[0037] The first spatial metadata may be obtained together with the corresponding audio signal. For example, in the system 101 of FIG. 1, the decoder 109 may obtain a bitstream 107 including both the one or more audio signals and the corresponding first spatial metadata. A reference to an audio signal or a transport audio signal may be a reference to one or more audio signals or one or more transport audio signals.

[0038] At block 203, the method includes determining second spatial metadata using the first spatial metadata, the second spatial metadata being different from the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals.

[0039] The second audio format may be different from the first audio format, for example, if the first audio format is FOA audio, the second audio format may be a binaural format or other suitable format.

[0040] In some examples, determining the second spatial metadata using the first spatial metadata includes determining rendering information from the first spatial metadata. The second spatial metadata may then be calculated from the rendering information. The rendering information may include any information indicating how the audio signal 103 associated with the first spatial metadata should be mixed and / or decorrelated to produce an audio output in the first format. The rendering information may include one or more mixing matrices.

[0041] In some examples, determining the second spatial metadata using the first spatial metadata may include directly calculating the second spatial metadata from the first spatial metadata. In such examples, the second spatial metadata may be calculated without determining intermediate rendering information.

[0042] In some examples, different types of spatial metadata may be used to render different frequencies of the spatial audio. For example, general spatial metadata may be used to render a first set of frequencies of the spatial audio, and additional format-specific spatial metadata may be used for a second set of frequencies. The first set of frequencies may be higher frequencies, and the second set of frequencies may be lower frequencies.

[0043] The general spatial metadata may include spatial metadata that can enable rendering to any output format or to multiple different output formats. The general spatial metadata may include information indicating sound direction and information indicating sound directivity for one or more frequency subbands. Sound directivity may be an indication of how directional or non-directional the sound is. Sound directivity may provide an indication of whether the sound is ambient sound or provided from a point source. Sound directivity may be provided as an energy ratio of direct sound to ambient sound or in other suitable formats. In some examples, the spatial metadata includes one or more coherence parameters or other suitable parameters.

[0044] At block 205, the method includes using the second spatial metadata and the one or more audio signals to enable rendering of spatial audio.

[0045] Thus, the example method allows the second spatial metadata to be determined without first rendering the spatial audio in a first format, which can provide improved quality in the spatial audio output 111.

[0046] Figure 3 illustrates in schematic form an example decoder 109. The example decoder 109 may be provided in a system 101, such as the system of Figure 1. The example decoder 109 may be configured to perform a method, such as the method of Figure 2, to enable spatial audio to be rendered in a format different from the format in which it was acquired.

[0047] The decoder 109 receives as input a bitstream 107. The bitstream 107 may include first spatial metadata and a corresponding audio signal. The bitstream 107 is provided to a demultiplexer 301. The demultiplexer 301 is configured to demultiplex the bitstream 107 into multiple streams. In the example of FIG. 3, the demultiplexer 301 demultiplexes the bitstream 107 into a first stream and a second stream. The first stream includes the encoded first spatial metadata 303 and the second stream includes the encoded transport audio signal 319.

[0048] The encoded transport audio signal 319 is provided to a transport audio signal decoder 321. The transport audio signal decoder 321 is configured to decode the encoded transport audio signal 319 and provide as an output a decoded transport audio signal 323. The process used to decode the encoded transport audio signal 319 may include a corresponding process used by the encoder 105 to encode the audio signal. The transport audio signal decoder 321 may include an Enhanced Voice Services (EVS) decoder, an Advanced Audio Coding (AAC) decoder, or any other suitable type of decoder.

[0049] The decoded transport audio signal 323 is provided to a time-frequency conversion block 325. The time-frequency conversion block 325 is configured to change the domain of the decoded transport audio signal 323. In some examples, the time-frequency conversion block 325 is configured to convert the decoded transport audio signal 323 into a time-frequency representation. The time-frequency conversion block 325 may be configured to use any suitable means to change the domain of the decoded transport audio signal 323. For example, the time-frequency conversion block 325 may be configured to use a short-time Fourier transform (STFT), a complex modulated quadrature mirror filter (QMF) bank, low-delay variants thereof, or other suitable means.

[0050] The time-to-frequency conversion block 325 provides as output a time-frequency transport audio signal 327 .

[0051] The encoded first spatial metadata 303 is provided as an input to a metadata decoder 305. The metadata decoder 305 is configured to decode the encoded first spatial metadata 303 and provide as output the decoded first spatial metadata 307. The process used to decode the encoded first spatial metadata 303 may include a corresponding process used by the encoder 105 to encode the first spatial metadata. The metadata decoder 305 may include any suitable type of decoder.

[0052] The format of the decoded first spatial metadata 307 depends on the first spatial audio format used to encode the audio signal. For example, if the audio signal is encoded for FOA rendering, the decoded first spatial metadata 307 will be in a format that enables FOA rendering. If the audio signal is encoded for binaural rendering, the decoded first spatial metadata 307 will be in a format that enables binaural rendering. In other examples, different types of audio formats may be used.

[0053] In an example where the first spatial audio format is FOA audio, the decoded first spatial metadata 307 may include FOA prediction coefficients or other suitable types of data. The FOA prediction coefficients include information that can be converted into rendering information, such as a mixing matrix. The rendering information or mixing matrix may include any information that indicates how audio signals should be mixed and / or decorrelated to produce an audio output in the first format.

[0054] The decoded first spatial metadata 307 is provided as an input to a mixing matrix determiner block 309. The mixing matrix determiner block 309 may be configured to determine one or more mixing matrices and / or any other suitable rendering information. The mixing matrix determiner block 309 provides a mixing matrix 311 as an output.

[0055] The mixing matrix may be determined based on the decoded first spatial metadata 307. The mixing matrix may be written as A(i,j,k,n), where i is the index of the output channel, j is the input channel, k is the frequency band, and n is the time frame. The mixing matrix may be applied to the transport audio signal and / or to a decorrelated version of the transport audio signal to render the FOA signal.

[0056] In other examples, other types of rendering information may be obtained. In some examples, rendering information need not be obtained. For example, the second spatial metadata may be obtained directly from the first spatial metadata. In some examples, the decoded first spatial metadata 307 may already be a mixing matrix or other rendering information, so in such examples, there is no need to use the mixing matrix determiner block 309.

[0057] In examples where the audio does not need to be converted to a second audio format, a mixing matrix, or other rendering information, can be used to render the decoded time-frequency transport audio signal 327. As an example, the decoded time-frequency transport audio signal 327 can be represented as a column vector s(b,n), where b is a frequency bin index and the rows of the vector represent the transport audio signal channels. The number of rows can be between 1 and 4, depending on the applied bit rate and other suitable factors. If the number of channels is less than four, the number of rows of the vector s(b,n) is also less than four. In such examples, the column vector can be appended with new channels to form a four-row vector s'(b,n). The new channels can be decorrelated versions of the original channel signals s(b,n).

[0058] The FOA signal is then y(b,n)=A(k,n)s'(b,n) where k is the frequency band that frequency bin b resides in. The spatial metadata for a frequency band can correspond to one or more frequency bins of the filter bank that was used to transform the audio signal.

[0059] In the above equation, the mixing matrix A can be written as:

number

[0060] This notation means that the time resolution of the signal s(b,n) and the time resolution of the mixing matrix A(k,n) (i.e., the time resolution of the metadata) are the same. This may be the case for the system 101 using a filter bank such as STFT configured to apply a coarse time resolution. The coarse time resolution may use a time step of the order of 20 milliseconds for the filter bank. Other filter banks may have a finer time resolution. In such a case, the resolution of the spatial metadata is sparser than the resolution of the audio signal. In such an example, the same mixing matrix may be applied to multiple different time indexes of the audio signal, or the mixing matrix may be interpolated in time.

[0061] In examples where the audio is converted to a second audio format, the mixing matrix, or other rendering information, may be used to determine the second spatial metadata instead of being used to render the spatial audio.

[0062] In such a case, the mixing matrix A(i,j,k,n) 311 is provided as an input to a second metadata determiner 313, as shown in Figure 3, which also receives a time-frequency transport audio signal 327 as input.

[0063] The second metadata determiner 313 is configured to determine second spatial metadata enabling rendering of the audio signal in a second audio format. The second metadata determiner 313 may be configured to determine the second spatial metadata 315 using the mixing matrix 311 and the time-frequency transport audio signal 327.

[0064] In this example, the second audio format is a binaural format. In other examples of the present disclosure, other formats may be used. For example, the second audio format may be a multi-channel loudspeaker format, or a higher order Ambisonic (HOA) format, or other suitable format. The second audio format may be a format other than the original format for which the first spatial metadata is intended.

[0065] In this example, the second spatial metadata 315 includes orientation (azimuth, elevation) θ(k,n), φ(k,n) parameters, and a direct-to-total energy ratio r(k,n) parameter. The parameters are provided in frequency bands. In other examples of the present disclosure, other types of parameters may be used.

[0066] To determine the second spatial metadata 315, the second metadata determiner 313 may first determine a covariance matrix of a signal s'(b,n) that is the time-frequency transport audio signal 327 to which a decorrelated version of the first channel has been added such that the time-frequency transport audio signal 327 comprises four channels. The covariance matrix may be formulated as follows:

number

[0067] where the superscript H stands for conjugate transpose, and b low (k) and b high (k) are the first and last bins of band k.

[0068] For parameter estimation purposes, only the covariance matrix is ​​needed, not the actual signal.

number

[0069] If the size of the covariance matrix obtained using this method is less than 4 × 4, the matrix can be zero-padded to a size of 4 × 4. The energy values ​​corresponding to the first channel can then be placed in the zero-padded diagonal elements in the matrix. This operation assumes that the decorrelated signals are generated from the first channel and that they are incoherent with respect to the first channel and with respect to each other. Thus, the result is a linear regression of the C without actually forming a decorrelated channel. s’ This is an estimate of (k,n).

[0070] In some embodiments, C s’ The estimation of (k,n) may also include time averaging over the time axis, which may be accomplished using infinite impulse response (IIR) averaging, finite impulse response (FIR) averaging, or other suitable types of time averaging.

[0071] And the FOA covariance matrix is C FOA (k,n)=A(k,n)C s’ (k,n)A H (k,n) It is formulated as follows:

[0072] At this time, C FOA Let the real part of the i-th row and j-th column of (k,n) be c i,j Denoted as (k,n), the directional parameters are θ(k,n)=atan2(c 1,2 (k,n),c 1,4 (k,n)

number

number

[0073] The second spatial metadata 315 provided as an output of the second metadata determiner 313 then includes the directions (azimuth, elevation) θ(k,n), φ(k,n), and the direct-to-total energy ratio r(k,n).

[0074] The second spatial metadata 315, the time-frequency transport audio signal 327 and the mixing matrix 311 are provided as inputs to a spatial synthesizer 317. The spatial synthesizer 317 is configured to use the second spatial metadata 315, the time-frequency transport audio signal 327 and the mixing matrix 311 to render the spatial audio output 111. The spatial audio output may be a binaural output or in any other suitable audio format.

[0075] 4 illustrates a schematic of an example spatial synthesizer 317. The example spatial synthesizer 317 may be provided in a decoder 109, such as the decoder 109 illustrated in FIG. 3. In this example, the second spatial metadata 315 includes a direct-to-total energy ratio and a direction. In other examples, the second spatial metadata 315 may include other parameters, such as spread and ambient coherence.

[0076] The spatial synthesizer 317 receives as input the second spatial metadata 315, a time-frequency transport audio signal 327 and the mixing matrix 311.

[0077] 4, the time-frequency transport audio signal 327 and the mixing matrix 311 are provided as inputs to a synthesis input generator 401. The synthesis input generator 401 is configured to convert the time-frequency transport audio signal 327 into a format suitable for processing by the rest of the blocks in the spatial synthesizer 317.

[0078] The process performed by the synthesis input generator 401 may depend on the number of transport channels used. In examples where the time-frequency transport audio signal 327 includes a single channel (mono transport), the synthesis input generator 401 may pass the time-frequency transport audio signal 327 through without performing any processing on the time-frequency transport audio signal 327. In some examples, a single channel signal may be replicated to create a signal including two or more channels. This may provide a dual-mono or pseudo-stereo signal.

[0079] In examples where the time-frequency transport audio signal 327 includes multiple channels, the synthesis input generator 401 may be configured to generate a stereo track, which may represent a cardioid pattern in different directions, such as to the left and to the right.

[0080] The cardioid pattern can be obtained using any suitable process. For example, the cardioid pattern can be obtained by applying a matrix A'(k,n) to the time-frequency transport audio signal 327. The matrix A'(k,n) includes the first two rows of the matrix A(k,n). This therefore provides the W and Y spherical harmonic signals.

[0081] After matrix A′(k,n) is applied, left and right cardioid beamforming matrices may be applied to provide preprocessed transport audio signal 403 .

[0082] The preprocessed transport audio signal x(b,n) 403 can be written as:

number

[0083] A pre-processed transport audio signal x(b,n) 403 is provided as an output of the synthesis input generator 401 .

[0084] The preprocessed transport audio signal 403 and the second spatial metadata 315 are provided as inputs to a covariance matrix determiner 411. The covariance matrix determiner 411 is configured to determine an input covariance matrix and a target covariance matrix, where the input covariance matrix represents the preprocessed transport audio signal 403 and the target covariance matrix represents the time-frequency spatial audio signal 407.

[0085] The input covariance matrix is ​​derived from the pre-processed transport audio signal 403 as

number

[0086] As mentioned above, in this example the time resolution of the covariance matrix is ​​the same as the time resolution of the audio signal, in other examples the time resolution may be different, for example in examples where a filter bank with high time selectivity is used.

[0087] covariance matrix C x (k,n) is

number

[0088] The target covariance matrix may be determined based on the second spatial metadata 315 and the overall signal energy.

[0089] The overall signal energy E(k,n) is x The second spatial metadata 315 may be obtained as an average of the diagonal values ​​of A'(k,n)s(b,n) or may be obtained based on the omnidirectional component of the signal A'(k,n)s(b,n). And in some examples, the second spatial metadata 315 includes the directions θ(k,n), φ(k,n) and the direct-to-global ratio parameter r(k,n). Assuming the output is a binaural signal, the target covariance matrix is C y (k,n)=E(k,n)r(k,n)h(k,θ(k,n),φ(k,n))h H (k,θ(k,n),φ(k,n))+E(k,n)(1-r(k,n))C d (k) Here, h(k,θ(k,n),φ(k,n)) is a column vector of the head-related transfer functions for band k and directions θ(k,n) and φ(k,n).

[0090] h(k,θ(k,n),φ(k,n)) is a column vector. The vector contains two values. The values ​​may be complex-valued. The values ​​correspond to the amplitude and phase of the Head Related Transfer Functions (HRTFs) for the left and right ear. At high frequencies, the phase difference is not needed for perceptual reasons, so at high frequencies the HRTF values ​​may contain real values.

[0091] Any suitable process can be used to obtain the HRTFs, which can be obtained for a given direction and frequency.

[0092] In the above formula, C d (k) is the diffuse field binaural covariance matrix. The diffuse field binaural covariance matrix can be determined in an offline stage. The diffuse field binaural covariance matrix can be determined using any suitable process, such as taking a set of spatially uniform HRTFs, formulating covariance matrices for them independently, and averaging the results.

[0093] The covariance matrix determiner 411 provides as output a covariance matrix 413. The covariance matrix 413 provided as output is a function of the input covariance matrix C x (k,n) and the target covariance matrix C y It may include (k,n).

[0094] In the above equations it is meant that the processing is done in a uniform manner within the bins of each band k. In some examples, the processing may be done at a higher frequency resolution, such as for each frequency bin b. In such examples, the equations given above are adapted such that the covariance matrix is ​​determined for each bin b, but using the parameters of the second spatial metadata 315 for the band k in which the bin resides.

[0095] In some examples, the input covariance matrix and the target covariance matrix may be time-averaged. The time averaging may be performed using infinite impulse response (IIR) averaging, finite impulse response (FIR) averaging, or other suitable types of time averaging. The covariance matrix determiner 411 may be configured to perform the time averaging such that a time-averaged covariance matrix 413 is provided as an output.

[0096] In this example, only parameters related to direction and energy ratio are considered to obtain the target covariance matrix. In other examples, other parameters may be considered in obtaining the target covariance matrix. For example, in addition to the direction and energy ratio, spatial coherence parameters, or other suitable parameters, may be considered. The use of other types of parameters may allow for providing spatial audio output in formats other than binaural formats and / or may improve the accuracy with which spatial sound may be reproduced.

[0097] The processing matrix determiner 415 determines the covariance matrix 413C x (k,n) and C y (k,n) as an input. The processing matrix determiner 415 is configured to determine the covariance matrix 413C x (k,n) and C y(k,n) to obtain the processing matrices M(k,n) and M r (k,n) are configured to determine the processing matrices M(k,n) and M r Any suitable process can be used to determine (k,n). In some examples, the process used involves determining the measured covariance matrix C x (k,n) to determine a mixing matrix for processing the audio signal, whereby they are combined with the determined target covariance matrix C y (k,n). Such a method can be used to generate binaural audio signals or surround loudspeaker signals, or other types of audio signals. To formulate the processing matrix, the method can include using a matrix such as a prototype matrix. A prototype matrix is ​​a matrix that indicates what type of signal is intended for each of the outputs for the optimization procedure. This can be within the constraint that the outputs must achieve a target covariance matrix. In an example where the second audio format is a binaural format, the prototype matrix can be as follows:

number

[0098] This prototype matrix indicates that the signal for the left ear is rendered primarily from the left pre-processed transport channel, and the signal for the right ear is rendered primarily from the right pre-processed transport channel. In some examples, the orientation of the user's head can be tracked. If it is determined that the user is currently facing towards the rear hemisphere, the prototype matrix becomes:

number

[0099] The processing matrix determiner 415 determines the processing matrices M(k,n) and M(k,n) based on the prototype matrix and the input and target covariance matrices using the means described in Vilkamo, J., Backstrom, T., Kuntz, A (2013), Optimized covariance domain framework for time-frequency processing of spatial audio, Journal of the Audio Engineering Society, 61(6), pp. 403-411. r The processing matrix determiner 415 may be configured to determine the processing matrices M(k,n) and M r (k,n) 417 as an output.

[0100] Processing matrices M(k,n) and M r The de-correlation and mixing block 405 receives the pre-processed transport audio signal x(b,n) 403 as an input. The de-correlation and mixing block 405 receives the processing matrices M(k,n) and M(k,n) 417 as an input. r The signal processor 402 may comprise any means that may be configured to decorrelate and mix the pre-processed transport audio signal x(b,n) 403 based on the pre-processed transport audio signal x(b,n) 417 .

[0101] Any suitable process can be used to decorrelate and mix the preprocessed transport audio signal x(b,n) 403. In some examples, decorrelation and mixing of the preprocessed transport audio signal x(b,n) 403 can be performed by processing the preprocessed transport audio signal x(b,n) 403 with the same prototype matrix applied by the processing matrix determiner 415 and decorrelating the result to produce a decorrelated signal x(b,n) 403. D (b,t) to generate the decorrelated signal x D(b,t) (and the pre-processed transport audio signal x(b,n) 403 ) may then be mixed using any suitable mixing procedure to produce a time-frequency audio signal 407 .

[0102] In some examples, the following mixing procedure is used to generate a time-frequency audio signal 407: y(b,t)=M(k,n)x(b,n)+M r (k,n)x D (b,n) where band k is the band in which bin b resides.

[0103] As mentioned before, the notation used here is that of the processing matrices M(k,n) and M r It means that the time resolution of the preprocessed transport audio signal x(b,n) 403 as well as the processing matrix 417 are the same. In other examples, they may have different time resolutions. For example, the time resolution of the processing matrix 417 may be sparser than the time resolution of the preprocessed transport audio signal 403. In such examples, an interpolation process such as linear interpolation may be applied to the processing matrix 417 to achieve the same time resolution of the preprocessed transport audio signal 403. The interpolation rate may depend on suitable factors. For example, the interpolation rate may depend on whether an onset has been detected. If an onset has been detected, fast interpolation may be used, and if an onset has not been detected, normal interpolation may be used.

[0104] The decorrelation and mixing block 405 provides a time-frequency spatial audio signal 407 as an output.

[0105] The time-frequency spatial audio signal 407 is provided as an input to an inverse filter bank 409. The inverse filter bank 409 is configured to apply an inverse transform to the time-frequency spatial audio signal 407. The inverse transform applied to the time-frequency spatial audio signal 407 may be a transform corresponding to the transform used to convert the decoded transport audio signal 323 into a time-frequency transport audio signal 327 in FIG.

[0106] The inverse filter bank 409 is configured to provide as an output the spatial audio output 111. The spatial audio output 111 is provided in a second audio format.

[0107] Different examples may use other methods instead of the covariance matrix based rendering than the example used in FIG. 4. For example, in other examples, the audio signal may be split into directional and omnidirectional parts. A ratio parameter from the spatial metadata may be used to split the signal into directional and omnidirectional parts. The directional parts may then be positioned to the virtual loudspeakers using amplitude panning or other suitable means. The omnidirectional parts may then be distributed to all loudspeakers and de-correlated. The processed directional and omnidirectional parts may then be added together. Each of the virtual loudspeakers may then be processed with an HRTF to obtain a binaural output. In such an example, the spatial synthesizer 317 comprises a synthesis input generator configured to generate a stereo signal from the time-frequency transport audio signal 327. The stereo signal is used to generate the virtual loudspeaker signals, whereby a left virtual loudspeaker signal is synthesized based on the left channel and a right virtual loudspeaker signal is synthesized based on the right channel.

[0108] Figure 5 illustrates in schematic form another example decoder 109. The example decoder 109 may also be provided in a system 101, such as the system of Figure 1. The example decoder 109 may be configured to perform a method, such as the method of Figure 2, to enable spatial audio to be rendered in a format different from the format in which it was acquired.

[0109] In the example of Fig. 5, the spatial metadata provided in the bitstream 107 includes different types of metadata. The different types of metadata may be used at different frequencies. For example, audio format specific metadata may be used at lower frequencies. The audio format specific metadata may be the first spatial metadata. General metadata may be used for higher frequencies.

[0110] The decoder 109 receives as input a bitstream 107. The bitstream 107 may include spatial metadata and a corresponding audio signal. The spatial metadata may include first spatial metadata that is audio format specific and general spatial metadata that is not format specific.

[0111] The bitstream 107 is provided to a demultiplexer 301. The demultiplexer 301 is configured to demultiplex the bitstream 107 into multiple streams. In this example of Fig. 3, the demultiplexer 301 demultiplexes the bitstream 107 into a first stream comprising the encoded spatial metadata and a second stream comprising the encoded transport audio signal.

[0112] The encoded transport audio signal 319 is provided to a transport audio signal decoder 321. The transport audio signal decoder 321 is configured to decode the encoded transport audio signal 319 and provide as an output a decoded transport audio signal 323. The decoded transport audio signal 323 is provided to a time-to-frequency conversion block 325. The time-to-frequency conversion block 325 provides as an output a time-frequency transport audio signal 327.

[0113] The transport audio signal decoder 321 and the time-to-frequency conversion block 325 may be as shown in FIG.

[0114] The encoded spatial metadata 501 is provided as an input to a metadata decoder 505. The encoded spatial metadata 501 includes both first spatial metadata and general spatial metadata. The metadata decoder 505 is configured to decode the encoded spatial metadata 501 and provide the decoded spatial metadata as an output. In this example, the metadata decoder 505 provides two streams of spatial metadata as an output. The first stream includes the decoded first spatial metadata 307 and the second stream includes the decoded general spatial metadata 503. The first spatial metadata 307 may be for use with lower frequencies and the general spatial metadata 503 may be for use with higher frequencies.

[0115] In this example, the general spatial metadata 503 is provided in a format that can be provided directly as input to the spatial synthesizer 317. The general spatial metadata 503 may include directional parameters, energy ratio parameters, diffuseness parameters, and / or other suitable parameters.

[0116] The decoded first spatial metadata 307 is provided as an input to a mixing matrix determiner block 309. The mixing matrix determiner block 309 may be configured to determine one or more mixing matrices and / or any other suitable rendering information. The mixing matrix determiner block 309 provides a mixing matrix 311 as an output. The mixing matrix determiner block 309 may be as shown in FIG.

[0117] The mixing matrix A(i,j,k,n) 311 is provided as an input to a second metadata determiner 313. The second metadata determiner 311 also receives a time-frequency transport audio signal 327 as an input. The second metadata determiner 313 is configured to determine second spatial metadata enabling rendering of the audio signal in a second audio format. The second metadata determiner 313 may be as shown in Fig. 3.

[0118] The second spatial metadata 315, the decoded general spatial metadata 503, the time-frequency transport audio signal 327 and the mixing matrix 311 are provided as inputs to a spatial synthesizer 317. The spatial synthesizer 317 is configured to render a spatial audio output 111 using the second spatial metadata 315, the decoded general spatial metadata 503, the time-frequency transport audio signal 327 and the mixing matrix 311. The spatial audio output may be a binaural output or in any other suitable audio format.

[0119] In the above examples, the second spatial metadata is determined from rendering information such as a mixing matrix. In other examples, the second spatial metadata can be determined directly from the first spatial metadata. For example, in the example of FIG. 3, the second spatial metadata can be determined from the decoded first spatial metadata without determining an intermediate mixing matrix.

[0120] In these examples, the parameters in the spatial metadata are limited to direction and energy ratio for simplicity. In other embodiments, other parameters may be included in the spatial metadata. For example, in some examples, the spatial metadata may include an ambient coherence parameter γ(k,n), or any other suitable parameter. The ambient coherence parameter may be a parameter that is added to the FOA audio signal C. FOA It can be determined based on the diagonal values ​​of the covariance matrix for (k,n). If the omnidirectional energy is large relative to the primary energy, the sound can be considered to have ambient coherence.

[0121] In the above example, the spatial audio output 111 is a binaural output. In other examples, other types of spatial audio output can be used and the processes and components can be configured accordingly. For example, if the spatial audio output is an HOA output, a combined approach can be used. In the combined approach, the zeroth and first orders can be rendered using the mixing matrix A(i,j,k,n) 311 as described above. Higher orders can be rendered by using the second spatial metadata 315 to render them. The spatial synthesizer 317 can be configured to render the higher orders using the second spatial metadata 315.

[0122] As an example, the direction of the second spatial metadata 315 can be used to determine the Ambisonic panning gain for a given order.

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[0124] 6 illustrates an example device 601 that can be used to implement examples of the present disclosure. The device 601 can be an electronic device such as a telephone, a camera, a computing device, a teleconferencing device, or any other suitable type of device.

[0125] Device 601 as shown in Figure 6 comprises a processor 603, a memory 605, a transceiver 609, and a digital-to-analog converter (DAC) 611. Device 601 may also comprise additional components not shown in Figure 6. For example, device 601 may include a display, a user interface, a microphone, a loudspeaker, a connection means for connecting to peripheral devices such as headphones, and other suitable components.

[0126] The transceiver 609 may be configured to receive a signal from a remote device. The transceiver 609 may be configured to receive a signal via any suitable communication network. In the example of Figure 6, the transceiver 609 is configured to receive a bitstream 103. The bitstream 103 may include a transport audio signal and corresponding spatial metadata.

[0127] The bitstream 103 is provided to a processor 603. The processor 603 may be configured to provide the functionality of a decoder 109 as shown in the system of Figure 1. The functionality of the encoder 105 is performed by a remote device from which the bitstream originates.

[0128] The processor 603 may be configured to access one or more computer programs 607 stored in the memory 605 of the device 601. The one or more computer programs 607 may be configured to enable the processor to perform the methods and processes described herein.

[0129] The processor provides a spatial audio output 111 as an output. This output may include a pulse code modulation (PCM) signal, or any other suitable type of signal. The spatial audio output 111 is provided to a DAC 111. The DAC 111 is configured to convert the digital signal to an appropriate analog signal for playback. In this example, the spatial audio output 111 includes a binaural signal, and the device used for playback includes headphones or a headset. In other examples, other types of devices may be used for playback. The playback device allows the user to hear the sound.

[0130] 7 illustrates a schematic diagram of an example apparatus 701 that may be used in some examples of the present disclosure. The apparatus 701 may comprise a controller apparatus and may be provided within the electronic device 601 as illustrated in FIG. 6. In the example of FIG. 7, the apparatus 701 comprises at least one processor 603 and at least one memory 605. It should be understood that the apparatus 701 may include additional components not illustrated in FIG.

[0131] 7, an embodiment of device 701 may be implemented as a processing circuit. In some examples, device 701 may be implemented solely in hardware, have certain aspects solely in software, including firmware, or be a combination of hardware and software (including firmware).

[0132] As shown in FIG. 7, the apparatus 701 may be implemented using instructions enabling hardware functionality, for example, using executable instructions of a computer program 607 in a general-purpose or special-purpose processor 603, and such computer program 607 may be stored in a computer-readable storage medium (disk, memory, etc.) for execution by such processor 603.

[0133] The processor 603 is configured to read from and write to the memory 605. The processor 603 may also include an output interface and an input interface through which data and / or commands are output by the processor 603 and through which data and / or commands are input to the processor 603.

[0134] The memory 605 is configured to store a computer program 607 including computer program instructions (computer program code 705) that, when loaded into the processor 603, controls the operation of the device 701. The computer program instructions of the computer program 607 provide logic and routines that enable the device 701 to perform the methods illustrated in Figures 2 to 5. The processor 603 is able to load and execute the computer program 607 by reading the memory 605.

[0135] Thus, the device 701 comprises: at least one processor 603 and at least one memory 605 containing computer program code 705, the at least one memory 605 and the computer program code 705 being configured by the at least one processor 603 to cause the device 701 to perform at least: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; Enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals. It is configured as follows.

[0136] As shown in FIG. 1, the computer program 607 can reach the device 701 via any suitable delivery mechanism 703. The delivery mechanism 703 can be, for example, a machine-readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a recording medium such as a compact disc read-only memory (CD-ROM) or a digital versatile disc (DVD), or a solid-state memory, an article of manufacture that includes or tangibly embodies the computer program 607. The delivery mechanism can be a signal configured to reliably transfer the computer program 607. The device 701 can propagate or transmit the computer program 607 as a computer data signal. In some examples, the computer program 607 can be a wireless communication device such as Bluetooth, Bluetooth Low Energy, Bluetooth Smart, 6LoWPan (IP v The information may be transmitted to the device 701 using a wireless protocol such as ZigBee, ANT+, Near Field Communication (NFC), Radio Frequency Identification, Wireless Local Area Network (WLAN), or other suitable protocol.

[0137] The computer program 607 causes the device 607 to at least: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; Enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals. The present invention includes computer program instructions for causing the computer to perform the steps of the method.

[0138] The computer program instructions may be included in a computer program 607, a non-transitory computer readable medium, a computer program product, a machine readable medium, etc. In some, but not necessarily all, examples, the computer program instructions may be distributed across multiple computer programs 607.

[0139] Although memory 605 is illustrated as a single component / circuit, it may be implemented as one or more separate components / circuits, some or all of which may be integrated / removable and / or provide permanent / semi-permanent / dynamic / cached storage.

[0140] Although the processor 603 is shown as a single component / circuit, it may be implemented as one or more separate components / circuits, some or all of which may be integrated / removable. The processor 603 may be a single core or a multi-core processor.

[0141] References to a "computer-readable storage medium," "computer program product," "tangibly embodied computer program," etc., or to a "controller," "computer," "processor," etc., should be understood to encompass computers having different architectures, such as single / multi-processor architectures, and sequential (von Neumann) / parallel architectures, as well as specialized circuitry, such as field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), signal processing devices, and other processing circuitry. References to computer programs, instructions, code, etc., should be understood to encompass software or firmware for a programmable processor, such as the programmable contents of a hardware device, whether, for example, instructions for a processor or configuration settings for a fixed function device, gate array, programmable logic device, etc.

[0142] As used in this application, the term "circuitry" may refer to one or more or all of the following: (a) a hardware-only circuit realization (e.g., an analog and / or digital only realization); (b) Combination of hardware circuitry and software (if applicable): (i) A combination of analog and / or digital hardware circuitry and software / firmware. (ii) Any portion of hardware processors (including digital signal processors), software, and memory with software that work together to cause a device, such as a mobile phone or server, to perform various functions. (c) A hardware circuit and / or processor, such as a microprocessor or part of a microprocessor, that requires software (e.g., firmware) to operate, but that the software may not be present when it is not necessary for operation.

[0143] This definition of circuitry applies to all uses of the term in this application, including any claims. As a further example, the term circuitry, as used in this application, also covers embodiments simply of hardware circuits or processors and their (or their) accompanying software and / or firmware. The term circuitry also covers, for example, baseband integrated circuits for mobile devices, or similar integrated circuits in servers, cellular network devices, or other computing or network devices, if applicable to certain claim elements.

[0144] 2-5 may represent steps in a method and / or sections of code in the computer program 607. The illustration of a particular order to the blocks does not necessarily imply a required or preferred order for the blocks, and the order and arrangement of the blocks may be varied. Additionally, some blocks may be omitted.

[0145] The term "comprise" is used in this document in an inclusive rather than exclusive sense, i.e. a reference to "X comprising Y" indicates that X may comprise only one Y or may comprise multiple Ys. Where the use of "comprise" in an exclusive sense is intended, this will be made clear in the context by a reference to "comprising only one" or by using "consisting".

[0146] Reference has been made herein to various examples. A description of a feature or functionality with respect to one example indicates that such feature or functionality is present in that example. Use of the terms "example" or "for example" or "can" or "may" in this text indicates that such feature or functionality is present in at least that described example, and may, but not necessarily, be present in some or all of the other examples, whether or not explicitly described as an example. Thus, "example," "for example," "can," or "may" refers to a particular instance in a class of examples. The nature of an instance may be a nature of that instance only, or of a class, or of a subclass of the class that includes some but not all of the instances of that class. Thus, a feature described with reference to one example but not described with reference to another example is implicitly disclosed as being capable of being used in that other example, but not necessarily being used in that other example, where possible, as part of a functional combination.

[0147] Although the examples have been described in the preceding paragraphs with reference to various examples, it will be appreciated that modifications can be made to the examples given without departing from the scope of the claims.

[0148] The features set out in the preceding description may also be used in combinations other than those explicitly set out above.

[0149] Although functions have been described with reference to particular features, these functions may be performed by other features, whether or not described.

[0150] Although features have been described with reference to particular examples, these features may be present in other examples, whether or not they are described.

[0151] In this document, the terms "a" or "the" are used in an inclusive, not exclusive sense. That is, a reference to "X comprising a / the Y" indicates that X may comprise only one Y or may comprise multiple Ys, unless the context clearly indicates the contrary. If the use of "a" or "the" in an exclusive sense is intended, it will be made clear in the context. In some circumstances, the use of "at least one" or "one or more" may be used to emphasize the inclusive sense, but the absence of these terms should not be taken to imply an exclusive sense.

[0152] The presence of a feature (or combination of features) in a claim is not only a reference to that feature or (combination of features) per se, but also to features that achieve substantially the same technical effect (equivalent features). Equivalent features include, for example, features that are modifications and achieve substantially the same result in substantially the same way. Equivalent features include, for example, features that perform substantially the same function in substantially the same way and achieve substantially the same result.

[0153] This description refers to various examples using adjectives or adjectival language to describe properties of the examples. Such description of a property with respect to the examples indicates that the property exists in some examples exactly as described and in other examples substantially as described.

[0154] Although the foregoing specification has attempted to draw attention to the features believed to be important, it should be understood that applicants may seek protection in the following claims with respect to any patentable feature or combination of features referred to in this specification and / or illustrated in the drawings, whether or not emphasized.

Claims

1. An apparatus comprising: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; Enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals An apparatus comprising:

2. 2. The apparatus of claim 1, wherein determining the second spatial metadata using the first spatial metadata comprises: determining rendering information from the first spatial metadata; and calculating the second spatial metadata from the rendering information.

3. The apparatus of claim 2 , wherein the rendering information comprises one or more mixing matrices.

4. The apparatus of claim 1 , wherein determining the second spatial metadata using the first spatial metadata comprises directly computing the second spatial metadata from the first spatial metadata.

5. 5. The apparatus of claim 1, wherein determining the second spatial metadata using the first spatial metadata is based on one or more audio signals.

6. 6. The apparatus of claim 1 , wherein determining the second spatial metadata using the first spatial metadata comprises determining one or more covariance matrices of the one or more audio signals.

7. 7. Apparatus according to any one of claims 1 to 6, wherein the means is for determining the second spatial metadata without rendering the spatial audio in the first audio format.

8. 8. Apparatus according to any one of claims 1 to 7, wherein means are for enabling different types of spatial metadata to be used to render different frequencies of the spatial audio.

9. 9. The apparatus of claim 8, wherein general spatial metadata is used to render a first set of frequencies of spatial audio and further format-specific spatial metadata is used for a second set of frequencies.

10. 10. The apparatus of claim 1, wherein the audio formats include one or more of the following: an ambisonic format, a binaural format, a multi-channel loudspeaker format.

11. 11. An apparatus according to any preceding claim, wherein the spatial metadata comprises information enabling mixing of audio signals to enable rendering of spatial audio in a selected audio format.

12. The spatial metadata, for one or more frequency subbands, Sound direction, and Sound Directivity 12. The apparatus of claim 1 , further comprising information indicative of at least one of:

13. 13. An apparatus according to claim 1, wherein the spatial metadata comprises one or more prediction coefficients for one or more frequency subbands.

14. An apparatus according to claim 1 , wherein the spatial metadata comprises one or more coherence parameters.

15. 15. An electronic device comprising an apparatus according to any one of claims 1 to 14, wherein the electronic device is at least one of a telephone, a camera, a computing device, and a teleconferencing device.

16. 1. A method comprising: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals; A method comprising:

17. 17. The method of claim 16, wherein determining the second spatial metadata using the first spatial metadata comprises: determining rendering information from the first spatial metadata; and calculating the second spatial metadata from the rendering information.

18. The method of claim 17 , wherein the rendering information includes one or more mixing matrices.

19. A computer program comprising computer program instructions which, when executed by a processing circuit, obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals; A computer program that causes

20. 20. The computer program product of claim 19, wherein determining the second spatial metadata using the first spatial metadata comprises determining rendering information from the first spatial metadata and calculating the second spatial metadata from the rendering information.

21. An apparatus comprising at least one processor and at least one memory containing computer program code, the at least one memory and the computer program code being configured to be transmitted by the at least one processor to the apparatus for at least: obtaining an encoded spatial audio signal comprising one or more audio signals and first spatial metadata, the first spatial metadata configured to enable rendering of spatial audio in a first audio format from the one or more audio signals; determining second spatial metadata using at least the first spatial metadata, the second spatial metadata enabling rendering of spatial audio in a second audio format from the one or more audio signals; Enabling rendering of spatial audio in a second audio format using at least the second spatial metadata and the one or more audio signals. The apparatus is configured so as to

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