EP3991170A1 - Détermination de codage de paramètre audio spatial et décodage associé - Google Patents

Détermination de codage de paramètre audio spatial et décodage associé

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Publication number
EP3991170A1
EP3991170A1 EP20833011.8A EP20833011A EP3991170A1 EP 3991170 A1 EP3991170 A1 EP 3991170A1 EP 20833011 A EP20833011 A EP 20833011A EP 3991170 A1 EP3991170 A1 EP 3991170A1
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EP
European Patent Office
Prior art keywords
mapping
directional
values
index
indices
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20833011.8A
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German (de)
English (en)
Other versions
EP3991170A4 (fr
Inventor
Adriana Vasilache
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Nokia Technologies Oy
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Nokia Technologies Oy
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Publication date
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Publication of EP3991170A1 publication Critical patent/EP3991170A1/fr
Publication of EP3991170A4 publication Critical patent/EP3991170A4/fr
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/008—Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/02—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders
    • G10L19/032—Quantisation or dequantisation of spectral components
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/02—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders
    • G10L19/0204—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders using subband decomposition
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
    • G10L19/16—Vocoder architecture
    • G10L19/18—Vocoders using multiple modes
    • G10L19/22—Mode decision, i.e. based on audio signal content versus external parameters
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
    • G10L19/16—Vocoder architecture
    • G10L19/18—Vocoders using multiple modes
    • G10L19/24—Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/002—Dynamic bit allocation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
    • H04S2420/03—Application of parametric coding in stereophonic audio systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04S—STEREOPHONIC SYSTEMS 
    • H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
    • H04S2420/11—Application of ambisonics in stereophonic audio systems

Definitions

  • the present application relates to apparatus and methods for sound-field related parameter encoding, but not exclusively for time-frequency domain direction related parameter encoding for an audio encoder and decoder.
  • Parametric spatial audio processing is a field of audio signal processing where the spatial aspect of the sound is described using a set of parameters.
  • parameters such as directions of the sound in frequency bands, and the ratios between the directional and non-directional parts of the captured sound in frequency bands.
  • These parameters are known to well describe the perceptual spatial properties of the captured sound at the position of the microphone array.
  • These parameters can be utilized in synthesis of the spatial sound accordingly, for headphones binaurally, for loudspeakers, or to other formats, such as Ambisonics.
  • the directions and direct-to-total energy ratios in frequency bands are thus a parameterization that is particularly effective for spatial audio capture.
  • a parameter set consisting of a direction parameter in frequency bands and an energy ratio parameter in frequency bands (indicating the directionality of the sound) can be also utilized as the spatial metadata (which may also include other parameters such as coherence, spread coherence, number of directions, distance etc) for an audio codec.
  • these parameters can be estimated from microphone-array captured audio signals, and for example a stereo signal can be generated from the microphone array signals to be conveyed with the spatial metadata.
  • the stereo signal could be encoded, for example, with an AAC encoder.
  • a decoder can decode the audio signals into PCM signals and process the sound in frequency bands (using the spatial metadata) to obtain the spatial output, for example a binaural output.
  • the aforementioned solution is particularly suitable for encoding captured spatial sound from microphone arrays (e.g., in mobile phones, VR cameras, stand alone microphone arrays).
  • microphone arrays e.g., in mobile phones, VR cameras, stand alone microphone arrays.
  • a further input for the encoder is also multi-channel loudspeaker input, such as 5.1 or 7.1 channel surround inputs.
  • the directional components of the metadata which may comprise an elevation, azimuth (and energy ratio which is 1 -diffuseness) of a resulting direction, for each considered time/frequency subband. Quantization of these directional components is a current research topic.
  • an apparatus comprising means configured to: generate spatial audio signal directional metadata parameters for a time-frequency tile; generate at least one mapping between values of the spatial audio signal directional metadata parameter are mapped to an index value; generate indices associated with the spatial audio signal directional metadata parameters based on the at least one mapping; and encode the indices based on an estimate of the number of bits required to encode the indices.
  • the means configured to encode the indices based on an estimate of the number of bits required to encode the indices may be configured to: estimate the number of bits required to entropy encode the indices based on a first mapping from the at least one mapping for the time-frequency tile; determine whether the number of bits required is greater than a determined threshold value and when the number of bits required is greater than the determined number of bits then: estimate a further number of bits required to encode indices based on at least one further mapping from the at least one mapping for the time-frequency tile, wherein the at least one further mapping reduces a possible number of index values to be encoded; select one of the at least one further mapping based on a lowest number of bits required; and encode the indices based on the selected one of the at least one further mapping.
  • the at least one further mapping may comprise at least one of: mapping an index value of 0 to a directional value of 0 and mapping increasing index values to increasing positive and negative directional values; mapping indices such that a directional value 0 (corresponding to front direction) is mapped to index 0 and the directional values corresponding to directions from left or right are alternatively allocated to increasing index values; mapping of indices such that a directional value 0 (corresponding to front direction) is mapped to index 0 and the directional values corresponding to directions from up or down are alternatively allocated to increasing index values; and mapping a mean removed index value to directional values.
  • the at least one further mapping may comprise at least one of: mapping index values to directional values for only one hemisphere; and mapping a single index value to a range of directional values.
  • the at least one further mapping may comprise a complementary mapping to the first mapping.
  • the encoding of the indices based on at least one further mapping may comprise at least one of: entropy encoding; and fixed rate encoding.
  • the at least one mapping may comprise at least one of: mapping an index value of 0 to a directional value of 0 and mapping increasing index values to increasing positive and negative directional values; mapping indices such that a directional value 0 (corresponding to front direction) is mapped to index 0 and the directional values corresponding to directions from left or right are alternatively allocated to increasing index values; mapping of indices such that a directional value 0 (corresponding to front direction) is mapped to index 0 and the directional values corresponding to directions from up or down are alternatively allocated to increasing index values; mapping index values to directional values for only one hemisphere; mapping a single index value to a range of directional values; and mapping a mean removed index value to directional values.
  • a method comprising: generating spatial audio signal directional metadata parameters for a time- frequency tile; generating at least one mapping between values of the spatial audio signal directional metadata parameter are mapped to an index value; generating indices associated with the spatial audio signal directional metadata parameters based on the at least one mapping; and encoding the indices based on an estimate of the number of bits required to encode the indices.
  • the encoding of the indices based on an estimate of the number of bits required to encode the indices may comprise: estimating the number of bits required to entropy encode the indices based on a first mapping from the at least one mapping for the time-frequency tile; determining whether the number of bits required is greater than a determined threshold value and when the number of bits required is greater than the determined number of bits then: estimating a further number of bits required to encode indices based on at least one further mapping from the at least one mapping for the time-frequency tile, wherein the at least one further mapping reduces a possible number of index values to be encoded; selecting one of the at least one further mapping based on a lowest number of bits required; and encoding the indices based on the selected one of the at least one further mapping.
  • the at least one further mapping may comprise at least one of: mapping an index value of 0 to a directional value of 0 and mapping increasing index values to increasing positive and negative directional values; mapping indices such that a directional value 0 (corresponding to front direction) is mapped to index 0 and the directional values corresponding to directions from left or right are alternatively allocated to increasing index values; mapping of indices such that a directional value 0 (corresponding to a reference direction which may be a front direction) is mapped to index 0 and the directional values corresponding to directions from up or down are alternatively allocated to increasing index values; and mapping a mean removed index value to directional values.
  • the at least one further mapping may comprise at least one of: mapping index values to directional values for only one hemisphere; and mapping a single index value to a range of directional values.
  • the at least one further mapping may comprise a complementary mapping to the first mapping.
  • Encoding of the indices based on at least one further mapping may comprise at least one of: encoding of the indices by entropy encoding; and encoding of the indices by fixed rate encoding.
  • the mapping may comprise at least one of: mapping an index value of 0 to a directional value of 0 and mapping increasing index values to increasing positive and negative directional values; mapping indices such that a directional value 0 (corresponding to a reference direction which may for example be a front direction) is mapped to index 0 and the directional values corresponding to directions from left or right are alternatively allocated to increasing index values; mapping of indices such that a directional value 0 (corresponding to front direction) is mapped to index 0 and the directional values corresponding to directions from up or down are alternatively allocated to increasing index values; mapping index values to directional values for only one hemisphere; mapping a single index value to a range of directional values; and mapping a mean removed index value to directional values.
  • an apparatus comprising at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: generate spatial audio signal directional metadata parameters for a time-frequency tile; generate at least one mapping between values of the spatial audio signal directional metadata parameter are mapped to an index value; generate indices associated with the spatial audio signal directional metadata parameters based on the at least one mapping; and encode the indices based on an estimate of the number of bits required to encode the indices.
  • the apparatus caused to encode the indices based on an estimate of the number of bits required to encode the indices may be caused to: estimate the number of bits required to entropy encode the indices based on a first mapping from the at least one mapping for the time-frequency tile; determine whether the number of bits required is greater than a determined threshold value and when the number of bits required is greater than the determined number of bits then: estimate a further number of bits required to encode indices based on at least one further mapping from the at least one mapping for the time-frequency tile, wherein the at least one further mapping reduces a possible number of index values to be encoded; select one of the at least one further mapping based on a lowest number of bits required; and encode the indices based on the selected one of the at least one further mapping.
  • the at least one further mapping may comprise at least one of: mapping an index value of 0 to a directional value of 0 and mapping increasing index values to increasing positive and negative directional values; mapping indices such that a directional value 0 (corresponding to a reference direction which may be a front direction) is mapped to index 0 and the directional values corresponding to directions from left or right are alternatively allocated to increasing index values; mapping of indices such that a directional value 0 (corresponding to a reference direction which may be a front direction) is mapped to index 0 and the directional values corresponding to directions from up or down are alternatively allocated to increasing index values; mapping index values to directional values for only one hemisphere; mapping a single index value to a range of directional values; and mapping a mean removed index value to directional values.
  • the at least one further mapping may comprise a complementary mapping to the first mapping.
  • the apparatus caused to encode of the indices based on at least one further mapping may be caused to perform at least one of: entropy encoding; and fixed rate encoding.
  • the at least one mapping may comprise at least one of: mapping an index value of 0 to a directional value of 0 and mapping increasing index values to increasing positive and negative directional values; mapping indices such that a directional value 0 (corresponding to a reference direction which may be a front direction) is mapped to index 0 and the directional values corresponding to directions from left or right are alternatively allocated to increasing index values; mapping of indices such that a directional value 0 (corresponding to a reference direction which may be a front direction) is mapped to index 0 and the directional values corresponding to directions from up or down are alternatively allocated to increasing index values; mapping index values to directional values for only one hemisphere; mapping a single index value to a range of directional values; and mapping a mean removed index value to directional values.
  • an apparatus comprising: means for generating spatial audio signal directional metadata parameters for a time-frequency tile; generating at least one mapping between values of the spatial audio signal directional metadata parameter are mapped to an index value; generating indices associated with the spatial audio signal directional metadata parameters based on the at least one mapping; and encoding the indices based on an estimate of the number of bits required to encode the indices.
  • a computer program comprising instructions [or a computer readable medium comprising program instructions] for causing an apparatus to perform at least the following: generating spatial audio signal directional metadata parameters for a time-frequency tile; generating at least one mapping between values of the spatial audio signal directional metadata parameter are mapped to an index value; generating indices associated with the spatial audio signal directional metadata parameters based on the at least one mapping; and encoding the indices based on an estimate of the number of bits required to encode the indices.
  • a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the following: generating spatial audio signal directional metadata parameters for a time-frequency tile; generating at least one mapping between values of the spatial audio signal directional metadata parameter are mapped to an index value; generating indices associated with the spatial audio signal directional metadata parameters based on the at least one mapping; and encoding the indices based on an estimate of the number of bits required to encode the indices.
  • an apparatus comprising: generating circuitry configured to generate spatial audio signal directional metadata parameters for a time-frequency tile; generating circuitry configured to generate at least one mapping between values of the spatial audio signal directional metadata parameter are mapped to an index value; generating circuitry configured to generate indices associated with the spatial audio signal directional metadata parameters based on the at least one mapping; and encoding circuitry configured to encode the indices based on an estimate of the number of bits required to encode the indices.
  • a computer readable medium comprising program instructions for causing an apparatus to perform at least the following: generating spatial audio signal directional metadata parameters for a time-frequency tile; generating at least one mapping between values of the spatial audio signal directional metadata parameter are mapped to an index value; generating indices associated with the spatial audio signal directional metadata parameters based on the at least one mapping; and encoding the indices based on an estimate of the number of bits required to encode the indices.
  • An apparatus comprising means for performing the actions of the method as described above.
  • An apparatus configured to perform the actions of the method as described above.
  • a computer program comprising program instructions for causing a computer to perform the method as described above.
  • a computer program product stored on a medium may cause an apparatus to perform the method as described herein.
  • An electronic device may comprise apparatus as described herein.
  • a chipset may comprise apparatus as described herein.
  • Embodiments of the present application aim to address problems associated with the state of the art.
  • Figure 1 shows schematically a system of apparatus suitable for implementing some embodiments
  • Figure 2 shows schematically the metadata encoder according to some embodiments
  • Figure 3 show a flow diagram of the first operations of the metadata encoder as shown in Figure 2 according to some embodiments;
  • Figure 4 shows a flow diagram of later operations of the metadata encoder as shown in Figure 2 according to some embodiments
  • Figure 5 shows a flow diagram of the entropy encoding of the direction indices as shown in Figure 4 according to some embodiments
  • Figure 6 shows a further flow diagram of the entropy encoding of the direction indices as shown in Figure 4 according to some embodiments.
  • Figure 7 shows schematically an example device suitable for implementing the apparatus shown.
  • the input format may be any suitable input format, such as multi-channel loudspeaker, Ambisonics (FOA/FIOA) etc. It is understood that in some embodiments the channel location is based on a location of the microphone or is a virtual location or direction.
  • the output of the example system is a multi channel loudspeaker arrangement. Flowever it is understood that the output may be rendered to the user via means other than loudspeakers.
  • the multi channel loudspeaker signals may be generalised to be two or more playback audio signals.
  • the metadata consists at least of elevation, azimuth and the energy ratio of a resulting direction, for each considered time/frequency subband.
  • the direction parameter components, the azimuth and the elevation are extracted from the audio data and then quantized to a given quantization resolution.
  • the resulting indexes must be further compressed for efficient transmission. For high bitrate, high quality lossless encoding of the metadata is needed.
  • the concept as discussed hereafter is to reduce values of the variables to be encoded.
  • the reduction can be implemented in some embodiments for the case when there are a higher number of symbols.
  • the change can be performed by subtracting from the number of symbols available the index to be encoded and encoding the resulting difference.
  • this corresponds to having audio sources situated with a bias to the rear.
  • the change can also be implemented in some embodiments by checking if all indexes are even or if all indexes are odd and encoding the values divided by two.
  • this corresponds to having the audio sources mainly situated on the upper or the lower side of audio scene.
  • the encoding of the MASA metadata is configured to first estimate the number of bits for the directional data based on the values of the quantized energy ratios for each time frequency tile. Furthermore the entropy encoding of the original quantization resolution is tested. If the resulting sum is larger than the amount of available bits, the number of bits can be proportionally reduced for each time frequency tile such that it fits the available number of bits, however the quantization resolution is not unnecessarily adjusted when the bitrate allows it (for example in higher bitrates).
  • the system 100 is shown with an ‘analysis’ part 121 and a‘synthesis’ part 131 .
  • The‘analysis’ part 121 is the part from receiving the multi-channel loudspeaker signals up to an encoding of the metadata and downmix signal and the‘synthesis’ part 131 is the part from a decoding of the encoded metadata and downmix signal to the presentation of the re-generated signal (for example in multi-channel loudspeaker form).
  • the input to the system 100 and the‘analysis’ part 121 is the multi-channel signals 102.
  • a microphone channel signal input is described, however any suitable input (or synthetic multi-channel) format may be implemented in other embodiments.
  • the spatial analyser and the spatial analysis may be implemented external to the encoder.
  • the spatial metadata associated with the audio signals may be a provided to an encoder as a separate bit-stream.
  • the spatial metadata may be provided as a set of spatial (direction) index values.
  • the multi-channel signals are passed to a downmixer 103 and to an analysis processor 105.
  • the downmixer 103 is configured to receive the multi channel signals and downmix the signals to a determined number of channels and output the downmix signals 104.
  • the downmixer 103 may be configured to generate a 2 audio channel downmix of the multi-channel signals.
  • the determined number of channels may be any suitable number of channels.
  • the downmixer 103 is optional and the multi-channel signals are passed unprocessed to an encoder 107 in the same manner as the downmix signal are in this example.
  • the analysis processor 105 is also configured to receive the multi-channel signals and analyse the signals to produce metadata 106 associated with the multi-channel signals and thus associated with the downmix signals 104.
  • the analysis processor 105 may be configured to generate the metadata which may comprise, for each time-frequency analysis interval, a direction parameter 108 and an energy ratio parameter 1 10 (and in some embodiments a coherence parameter, and a diffuseness parameter).
  • the direction and energy ratio may in some embodiments be considered to be spatial audio parameters.
  • the spatial audio parameters comprise parameters which aim to characterize the sound-field created by the multi-channel signals (or two or more playback audio signals in general).
  • the parameters generated may differ from frequency band to frequency band.
  • band X all of the parameters are generated and transmitted, whereas in band Y only one of the parameters is generated and transmitted, and furthermore in band Z no parameters are generated or transmitted.
  • band Z no parameters are generated or transmitted.
  • a practical example of this may be that for some frequency bands such as the highest band some of the parameters are not required for perceptual reasons.
  • the downmix signals 104 and the metadata 106 may be passed to an encoder 107.
  • the encoder 107 may comprise an audio encoder core 109 which is configured to receive the downmix (or otherwise) signals 104 and generate a suitable encoding of these audio signals.
  • the encoder 107 can in some embodiments be a computer (running suitable software stored on memory and on at least one processor), or alternatively a specific device utilizing, for example, FPGAs or ASICs.
  • the encoding may be implemented using any suitable scheme.
  • the encoder 107 may furthermore comprise a metadata encoder/quantizer 1 1 1 which is configured to receive the metadata and output an encoded or compressed form of the information.
  • the encoder 107 may further interleave, multiplex to a single data stream or embed the metadata within encoded downmix signals before transmission or storage shown in Figure 1 by the dashed line.
  • the multiplexing may be implemented using any suitable scheme.
  • the received or retrieved data may be received by a decoder/demultiplexer 133.
  • the decoder/demultiplexer 133 may demultiplex the encoded streams and pass the audio encoded stream to a downmix extractor 135 which is configured to decode the audio signals to obtain the downmix signals.
  • the decoder/demultiplexer 133 may comprise a metadata extractor 137 which is configured to receive the encoded metadata and generate metadata.
  • the decoder/demultiplexer 133 can in some embodiments be a computer (running suitable software stored on memory and on at least one processor), or alternatively a specific device utilizing, for example, FPGAs or ASICs.
  • the decoded metadata and downmix audio signals may be passed to a synthesis processor 139.
  • the system 100‘synthesis’ part 131 further shows a synthesis processor 139 configured to receive the downmix and the metadata and re-creates in any suitable format a synthesized spatial audio in the form of multi-channel signals 1 10 (these may be multichannel loudspeaker format or in some embodiments any suitable output format such as binaural or Ambisonics signals, depending on the use case) based on the downmix signals and the metadata.
  • a synthesis processor 139 configured to receive the downmix and the metadata and re-creates in any suitable format a synthesized spatial audio in the form of multi-channel signals 1 10 (these may be multichannel loudspeaker format or in some embodiments any suitable output format such as binaural or Ambisonics signals, depending on the use case) based on the downmix signals and the metadata.
  • the system is configured to receive multi-channel audio signals. Then the system (analysis part) is configured to generate a downmix or otherwise generate a suitable transport audio signal (for example by selecting some of the audio signal channels). The system is then configured to encode for storage/transmission the downmix (or more generally the transport) signal. After this the system may store/transmit the encoded downmix and metadata. The system may retrieve/receive the encoded downmix and metadata. Then the system is configured to extract the downmix and metadata from encoded downmix and metadata parameters, for example demultiplex and decode the encoded downmix and metadata parameters.
  • the system (synthesis part) is configured to synthesize an output multi channel audio signal based on extracted downmix of multi-channel audio signals and metadata.
  • the analysis processor 105 in some embodiments comprises a time- frequency domain transformer 201 .
  • the time-frequency domain transformer 201 is configured to receive the multi-channel signals 102 and apply a suitable time to frequency domain transform such as a Short Time Fourier Transform (STFT) in order to convert the input time domain signals into a suitable time-frequency signals.
  • STFT Short Time Fourier Transform
  • These time-frequency signals may be passed to a spatial analyser 203 and to a signal analyser 205.
  • time-frequency signals 202 may be represented in the time-frequency domain representation by
  • n can be considered as a time index with a lower sampling rate than that of the original time-domain signals.
  • Each subband k has a lowest bin b k low and a highest bin b k,high , and the subband contains all bins from b k,low to b k,high .
  • the widths of the subbands can approximate any suitable distribution. For example the Equivalent rectangular bandwidth (ERB) scale or the Bark scale.
  • the analysis processor 105 comprises a spatial analyser 203.
  • the spatial analyser 203 may be configured to receive the time- frequency signals 202 and based on these signals estimate direction parameters 108.
  • the direction parameters may be determined based on any audio based ‘direction’ determination.
  • the spatial analyser 203 is configured to estimate the direction with two or more signal inputs. This represents the simplest configuration to estimate a‘direction’, more complex processing may be performed with even more signals.
  • the spatial analyser 203 may thus be configured to provide at least one azimuth and elevation for each frequency band and temporal time-frequency block within a frame of an audio signal, denoted as azimuth (p(k,n) and elevation 0(k,n).
  • the direction parameters 108 may be also be passed to a direction analyser/index generator 215.
  • the spatial analyser 203 may also be configured to determine an energy ratio parameter 1 10.
  • the energy ratio may be the energy of the audio signal considered to arrive from a direction.
  • the direct-to-total energy ratio r(k,n) can be estimated, e.g., using a stability measure of the directional estimate, or using any correlation measure, or any other suitable method to obtain a ratio parameter.
  • the energy ratio may be passed to an energy ratio average generator/quantization resolution determiner 21 1 .
  • the analysis processor is configured to receive time domain multichannel or other format such as microphone or Ambisonics audio signals.
  • the analysis processor may apply a time domain to frequency domain transform (e.g. STFT) to generate suitable time-frequency domain signals for analysis and then apply direction analysis to determine direction and energy ratio parameters.
  • a time domain to frequency domain transform e.g. STFT
  • the analysis processor may then be configured to output the determined parameters.
  • the parameters may be combined over several time indices. Same applies for the frequency axis, as has been expressed, the direction of several frequency bins b could be expressed by one direction parameter in band k consisting of several frequency bins b. The same applies for all of the discussed spatial parameters herein.
  • the audio spatial metadata consists of azimuth, elevation, and energy ratio data for each subband.
  • the directional data is represented on 16 bits such that the azimuth is approximately represented on 9 bits, and the elevation on 7 bits.
  • the energy ratio is represented on 8 bits.
  • the metadata encoder/quantizer 1 1 1 may comprise an energy ratio average generator/quantization resolution determiner 21 1 .
  • the energy ratio average generator/quantization resolution determiner 21 1 may be configured to receive the energy ratios and from the analysis and from this generate a suitable encoding of the ratios. For example to receive the determined energy ratios (for example direct- to-total energy ratios, and furthermore diffuse-to-total energy ratios and remainder- to-total energy ratios) and encode/quantize these. These encoded forms may be passed to the encoder 217.
  • the energy ratio average generator/quantization resolution determiner 21 1 thus may be configured to apply a scalar non-uniform quantization using 3 bits for each sub-band.
  • the energy ratio average generator/quantization resolution determiner 21 1 is configured to, rather than controlling the transmitting/storing of all of the energy ratio values for all TF blocks, generate only one weighted average value per subband which is passed to the encoder to be transmitted/stored.
  • this average is computed by taking into account the total energy of each time-frequency block and the weighting applied based on the subbands having more energy.
  • the energy ratio average generator/quantization resolution determiner 21 1 is configured to determine the quantization resolution for the direction parameters (in other words a quantization resolution for elevation and azimuth values) for all of the time-frequency blocks in the frame.
  • This bit allocation may for example be defined by bits_dir0[0:N-1 ][0:M-1 ] and may be passed to the direction analyser/index generator 215.
  • the actions of the energy ratio average generator/quantization resolution determiner 21 1 can be summarised.
  • the first step is one of receiving the ratio values as shown in Figure 3 by step 301 .
  • the subband loop is started in Figure 3 by step 303.
  • the subband loop comprises a first action of using a determined number of bits (for example 3) to represent the energy ratio value based on the weighted average of the energy ratio value for all of the values within the time block (where the weighting is determined by the energy value of the audio signal) as shown in Figure 3 by step 305.
  • the second action is one determined the quantization resolution for the azimuth and elevation for all of the time block of the current subband based on the value of the energy ratio as shown in Figure 3 by step 307.
  • the loop is closed in Figure 3 by step 309.
  • the metadata encoder/quantizer 1 1 1 may comprise a direction analyser/index generator 215.
  • the direction index generator 215 is configured to receive the direction parameters (such as the azimuth (p(k, n) and elevation 0(k, n) 108 and the quantization bit allocation and from this generate a quantized output.
  • the quantization is based on an arrangement of spheres forming a spherical grid arranged in rings on a‘surface’ sphere which are defined by a look up table defined by the determined quantization resolution.
  • the spherical grid uses the idea of covering a sphere with smaller spheres and considering the centres of the smaller spheres as points defining a grid of almost equidistant directions. The smaller spheres therefore define cones or solid angles about the centre point which can be indexed according to any suitable indexing algorithm.
  • spherical quantization is described here any suitable quantization, linear or non-linear may be used.
  • the bits for direction parameters are allocated according to the table bits_direction[]; if the energy ratio has the index /, the number of bits for the direction is bits_direction[/].
  • ‘no_theta’ corresponds to the number of elevation values in the ‘North hemisphere’ of the sphere of directions, including the Equator.‘no_phi’ corresponds to the number of azimuth values at each elevation for each quantizer.
  • the direction analyser/index generator 215 can then be configured to entropy encode the azimuth and elevation indices.
  • the entropy coding is implemented for one frequency subband at a time, encoding all the time subframes for that subband. This means that for instance the best GR order is determined for the 4 values corresponding to the time subframes of a current subband. Furthermore as discussed herein when there are several methods to encode the values for one subband one of the methods is selected as discussed later.
  • the entropy encoding of the azimuth and the elevation indexes in some embodiments may be implemented using a Golomb Rice encoding method with two possible values for the Golomb Rice parameter. In some embodiments the entropy coding may also be implemented using any suitable entropy coding technique (for example Huffman, arithmetic coding ).
  • the direction analyser/index generator 215 can then be configured to compare the number of bits used by the entropy coding EC to the number of bits available for encoding bits_dir1 [0:N-1 ][0:M-1]. This decision may be implemented at a subband level. In other words the EC bits for azimuth + the EC bits for elevation of the current subband, i, are compared to sum(bits_dir1 [i][0:M-1 ]).
  • the entropy coding based on the quantized direction indices are used.
  • the direction analyser/index generator 215 can then be configured to start a loop for each subband upto the penultimate subband N-1 .
  • the direction analyser/index generator 215 can be configured to encode the direction indices using the fixed rate encoding method and using bits_dir1 [N-1 ][0:M-1 ] bits.
  • the first step is one of determining the direction indices based on the quantization as shown in Figure 4 by step 400. Flaving determined the direction indices they are entropy encoded as shown in Figure 4 by step 401 . The number of bits used entropy encoding the direction indices are compared against the number of bit allowed as shown in Figure 4 by step 403. Where the number of bits used for entropy encoding the direction indices is less than (or equal to) the number of bits allowed then the entropy encoded direction indices can be used as shown in Figure 4 by step 404 and the method ends for this frame.
  • the number of bits used for entropy encoding the direction indices is more than the number of bits allowed then the number of allocated bits is reduced such that the sim of the allocated bits equals the number of available bits left after encoding the energy ratios as shown in Figure 4 by step 405.
  • the number of allowed bits for encoding is determined as shown in Figure 4 by step 409.
  • a fixed rate encoding method is used to encode the indices using the reduced number of bits as shown in Figure 4 by step 41 1 .
  • Either the fixed rate encoding or the entropy encoding is then selected based on which method uses fewer bits and the selection furthermore can be indicated by a single bit as shown in Figure 4 by step 413.
  • step 415 The determination of whether there are any remaining bits available based on the difference between the number of allowed bits and the number of bits used by the selected encoding and the redistribution of the remaining bits to the later subband allocations is shown in Figure 4 by step 415.
  • the loop is then completed and may then repeat for the next subband as shown in Figure 4 by step 417.
  • bits_allowed sum(bits_dir1 [i][0:M-1 ])
  • nb min(bits_fixed, bits_ec)+1 ;
  • the optimisation of the entropy encoding of the elevation and the azimuth values can be performed separately and is described in further detail hereafter with respect to Figures 5 and 6.
  • the direction indices determination is started as shown in Figure 5 by step 501 .
  • the bits required for entropy encoding the indices determination shown is an elevation index determination.
  • a similar approach may be applied to the azimuth index determination.
  • a mapping is generated such that the elevation (or azimuth) value of 0 has an index of 0 and the increasing index values are assigned to increasing positive and negative elevation (azimuth) values as shown in Figure 5 by step 503.
  • mapping is applied to the audio sources (for example in the form of generating a codeword output based on a lookup table) as shown in Figure 5 by step 505.
  • the indices having been generated in some embodiments there is a check performed to determine whether all of the indices are located within the same hemisphere as shown in Figure 5 by step 507.
  • the index values can be divided by two (with a rounding up) and an indicator generated indicating which hemisphere the indices were all located within and then entropy encoding these values as shown in Figure 5 by step 509.
  • a mean removed entropy encoding may be configured to remove first the average index value for the subframes to be encoded, then remap the indices to positive ones and then encode them with a suitable entropy encoding, such as Golomb Rice encoding as shown in Figure 5 by step 510.
  • a check can be applied to determine whether all of the time subframes have the same elevation (azimuth) value or index as shown in Figure 5 by step 51 1 .
  • the next operation is one of providing the number of bits required for the entropy encoded indices and any indicator bits as shown in Figure 5 by step 517.
  • the index of the elevation can be determined from a codebook in the domain [-90; 90] which is formed such that an elevation with a value 0 returns a codeword with index zero and alternatively assigns increasing indexes to positive and negative codewords distancing themselves from the zero elevation value.
  • the encoder can be configured to check whether all of the audio sources are above (or all of the audio sources are below) the equator and where this is the case for all time subframes for a subband then dividing the indices by 2, in order to generate smaller valued indices which can be more efficiently encoded.
  • the function mean_removed_GR() in the above example is configured to remove first the average index value for the subframes to be encoded, then remap the indices to positive ones and then encodes them with Golomb Rice encoding.
  • odd_even_mean_removed_GR() is configured to check first if all indexes are odd or if all are even, signals this occurrence and indicates the type (odd or even) after which it encodes the halved indices.
  • a series of entropy encoding optimisation operations are performed and then the lowest value is selected. This for example can be shown with respect to the encoding of azimuth values and as shown in Figure 6.
  • the direction indices determination is started as shown in Figure 6 by step 601 .
  • a mapping is generated such that the azimuth value of 0 has an index of 0 and the increasing index values are assigned to increasing positive and negative azimuth values as shown in Figure 6 by step 503.
  • mapping is applied to the audio sources (for example in the form of generating a codeword output based on a lookup table) as shown in Figure 6 by step 605.
  • the index of the azimuth can be determined from a further codebook.
  • the zero value for the azimuth corresponds to a reference direction which may be the front direction, and positive values are to the left and negative values to the right.
  • the index of the azimuth value is assigned such that the values (-150, -120, -90, -60, -30, 0, 30, 60, 90, 120, 150, 180) have assigned the following indices (10, 8, 6, 4, 2, 0, 1 , 3, 5, 7, 9, 1 1 ).
  • the odd/even approach can be checked for the azimuth (corresponding to left /right positioning).
  • the higher index values are assigned to values from the back or rear of the‘capture environment’.
  • i Estimate the number of bits if encoding the indexes as they would be in front. Use mean removed order selective Golomb Rice coding.
  • the GR order may be 2 or 3.
  • the GR order can also be set to different values, depending of the default range for the number of symbols.
  • ii Estimate the number of bits if encoding the complementary indexes using mean removed order selective GR coding.
  • iii Use the encoding method that uses the fewer number of bits and use a bit to signal which method is used
  • the device may be any suitable electronics device or apparatus.
  • the device 1400 is a mobile device, user equipment, tablet computer, computer, audio playback apparatus, etc.
  • the device 1400 comprises at least one processor or central processing unit 1407.
  • the processor 1407 can be configured to execute various program codes such as the methods such as described herein.
  • the device 1400 comprises a memory 141 1 .
  • the at least one processor 1407 is coupled to the memory 141 1 .
  • the memory 141 1 can be any suitable storage means.
  • the memory 141 1 comprises a program code section for storing program codes implementable upon the processor 1407.
  • the memory 141 1 can further comprise a stored data section for storing data, for example data that has been processed or to be processed in accordance with the embodiments as described herein. The implemented program code stored within the program code section and the data stored within the stored data section can be retrieved by the processor 1407 whenever needed via the memory-processor coupling.
  • the device 1400 comprises a user interface 1405.
  • the user interface 1405 can be coupled in some embodiments to the processor 1407.
  • the processor 1407 can control the operation of the user interface 1405 and receive inputs from the user interface 1405.
  • the user interface 1405 can enable a user to input commands to the device 1400, for example via a keypad.
  • the user interface 1405 can enable the user to obtain information from the device 1400.
  • the user interface 1405 may comprise a display configured to display information from the device 1400 to the user.
  • the user interface 1405 can in some embodiments comprise a touch screen or touch interface capable of both enabling information to be entered to the device 1400 and further displaying information to the user of the device 1400.
  • the user interface 1405 may be the user interface for communicating with the position determiner as described herein.
  • the device 1400 comprises an input/output port 1409.
  • the input/output port 1409 in some embodiments comprises a transceiver.
  • the transceiver in such embodiments can be coupled to the processor 1407 and configured to enable a communication with other apparatus or electronic devices, for example via a wireless communications network.
  • the transceiver or any suitable transceiver or transmitter and/or receiver means can in some embodiments be configured to communicate with other electronic devices or apparatus via a wire or wired coupling.
  • the transceiver can communicate with further apparatus by any suitable known communications protocol.
  • the transceiver can use a suitable universal mobile telecommunications system (UMTS) protocol, a wireless local area network (WLAN) protocol such as for example IEEE 802.X, a suitable short-range radio frequency communication protocol such as Bluetooth, or infrared data communication pathway (IRDA).
  • UMTS universal mobile telecommunications system
  • WLAN wireless local area network
  • IRDA infrared data communication pathway
  • the transceiver input/output port 1409 may be configured to receive the signals and in some embodiments determine the parameters as described herein by using the processor 1407 executing suitable code.
  • the various embodiments of the invention may be implemented in hardware or special purpose circuits, software, logic or any combination thereof.
  • some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto.
  • firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto.
  • While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
  • the embodiments of this invention may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware.
  • any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions.
  • the software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD.
  • the memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.
  • the data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi-core processor architecture, as non-limiting examples.
  • Embodiments of the inventions may be practiced in various components such as integrated circuit modules.
  • the design of integrated circuits is by and large a highly automated process.
  • Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.
  • Programs such as those provided by Synopsys, Inc. of Mountain View, California and Cadence Design, of San Jose, California automatically route conductors and locate components on a semiconductor chip using well established rules of design as well as libraries of pre-stored design modules.
  • the resultant design in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or "fab" for fabrication.

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Abstract

L'invention concerne un appareil comprenant des moyens conçus pour : générer des paramètres de métadonnées directionnels de signal audio spatial pour une mosaïque temps-fréquence; générer au moins un mappage (503) entre des valeurs du paramètre de métadonnées directionnel de signal audio spatial sont mappées sur une valeur d'indice (505); générer des indices associés aux paramètres de métadonnées directionnels de signal audio spatial sur la base de l'au moins un mappage; et coder les indices sur la base d'une estimation (517) du nombre de bits requis pour coder les indices.
EP20833011.8A 2019-06-25 2020-06-15 Détermination de codage de paramètre audio spatial et décodage associé Withdrawn EP3991170A4 (fr)

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