Spatial audio parameter encoding and associated decoding

Abstract

A method comprises: obtaining a first audio direction parameter value for each subband of a subframe of a frame of an audio signal; obtaining a second audio direction parameter value for the subframe of the frame of the audio signal for one or more audio objects associated with the audio signal; and determining a bit-efficient encoding for each first audio direction parameter value of the subframe based on a similarity between the first audio direction parameter value for each subband and the second audio direction parameter values ​​for the one or more audio objects.

Description

Technical Field

[0001] The present invention relates to encoding of sound field related parameters, but not exclusively to encoding of direction related parameters in the time-frequency domain for audio encoders and decoders. Background Art

[0002] Parametric spatial audio processing is the field of audio signal processing that uses a set of parameters to describe the spatial aspects of sound. For example, in parametric spatial audio capture from a microphone array, estimating a set of parameters from the microphone array signal, such as the direction of the sound in the frequency band, and the ratio of the directional to non-directional parts of the captured sound in the frequency band, is a typical and effective choice. It is well known that these parameters describe the perceived spatial characteristics of the captured sound at the location of the microphone array. These parameters can be used accordingly in the synthesis of spatial sound for binaural headphones, speakers, or other formats such as Ambisonics.

[0003] Therefore, the directionality and direct-to-total energy ratio in a frequency band are particularly effective parameterizations for spatial audio capture.

[0004] A parameter set including a directional parameter in a frequency band and an energy ratio parameter in a frequency band (indicating the directionality of the sound) can also be used as spatial metadata for an audio codec (which can also include other parameters such as coherence, spread coherence, number of directions, distance, etc.). For example, these parameters can be estimated from an audio signal captured by a microphone array, and, for example, a stereo signal can be generated from the microphone array signal to be transmitted together with the spatial metadata. The stereo signal can be encoded, for example, with an AAC encoder. The decoder can decode the audio signal into a PCM signal and process the sound in the frequency band (using the spatial metadata) to obtain a spatial output, for example, a binaural output.

[0005] The aforementioned solution is particularly suitable for encoding captured spatial sound from a microphone array (e.g., in a mobile phone, a VR camera, a stand-alone microphone array). However, it may be desirable for such an encoder to have other input types in addition to the signal captured by the microphone array, such as a speaker signal, an audio object signal, or an Ambisonics signal.

[0006] Analysis of First Order Ambisonics (FOA) input for spatial metadata extraction has been well documented in the scientific literature related to Directional Audio Coding (DirAC) and Harmonic Plane Wave Expansion (Harpex). This is because there are microphone arrays that directly provide FOA signals (more precisely: its variant, B-format signals), and therefore analysis of such input has become a research focus in this field.

[0007] Another input for the encoder is also a multi-channel speaker input, such as a 5.1 or 7.1 channel surround sound input.

[0008] The above process may involve obtaining directional parameters such as azimuth and elevation as well as energy ratios as spatial metadata through multi-channel analysis in the time-frequency domain. On the other hand, the directional metadata of each audio object may be processed in a separate processing chain. However, if the metadata is processed separately, the possible synergy in processing these two types of metadata is not effectively utilized. Summary of the invention

[0009] An improved method and a technical device for implementing the method have now been invented, whereby the above-mentioned problems are alleviated. Various aspects include a method, an apparatus and a non-transitory computer-readable medium including a computer program or a signal stored therein, characterized by what is stated in the independent claims. Various details of the embodiments are disclosed in the dependent claims and the corresponding drawings and description.

[0010] The scope of protection sought by various embodiments of the present invention is set out by the independent claims. Embodiments and features described in this specification that do not fall under the scope of the independent claims, if any, are to be construed as examples useful for understanding the various embodiments of the present invention.

[0011] According to a first aspect, a device is provided, comprising components for performing the following operations: obtaining a first audio direction parameter value for each subband of a subframe of a frame of an audio signal; obtaining a second audio direction parameter value for the subframe of the frame of the audio signal for one or more audio objects associated with the audio signal; and determining a bit-efficient encoding for each first audio direction parameter value for the subframe based on a similarity between the first audio direction parameter value for each subband and the second audio direction parameter values ​​for the one or more audio objects.

[0012] According to an embodiment, the first audio direction parameter and the second audio direction parameter are defined as points on the surface of a sphere.

[0013] According to an embodiment, the first audio direction parameter value comprises at least one azimuth value and at least one elevation value for each subband of the subframe, and the second audio direction parameter value comprises at least one azimuth value and at least one elevation value for each audio object.

[0014] According to an embodiment, the one or more audio objects are associated with a sub-frame of a frame of the audio signal or with a frame of the audio signal.

[0015] According to an embodiment, the bit-efficient encoding for the first audio direction parameter value includes: in response to the similarity between the second audio direction parameter value of the audio object and the first audio direction parameter value being lower than a predetermined threshold, encoding the index of the audio object as the first audio direction parameter value; or in response to the similarity between the second audio direction parameter value of the audio object and the first audio direction parameter value being higher than the predetermined threshold, encoding the first audio direction parameter value as a quantized first audio direction parameter value.

[0016] According to an embodiment, the means for determining a bit-efficient encoding for a first audio direction parameter value further comprises means for performing the following operations: determining, for each subband and subframe, a directionality difference between an original first audio direction parameter value and a quantized first audio direction parameter value; determining, for each subband and subframe, a directionality difference between an original first audio direction parameter value and a second audio direction parameter value of the audio object; determining a minimum value of the directionality difference between the original first audio direction parameter value and the second audio direction parameter value of the audio object; and using the minimum value in a similarity comparison between the first audio direction parameter value and the second audio direction parameter value.

[0017] According to an embodiment, the apparatus further comprises means for encoding in or with the bitstream an indication for indicating whether an index of the audio object is allowed to be encoded as the first audio direction parameter value.

[0018] According to an embodiment, the indication is audio frame specific.

[0019] According to an embodiment, the first audio direction parameter value further includes a signal energy value for each subband and subframe, and the second audio direction parameter value further includes a signal energy value for each subframe of each audio object; the device further includes a component for performing the following operations: based on the signal energy values ​​for the subframes and subbands and the signal energy values ​​of the audio objects for the subframes, determining a masking parameter, wherein the masking parameter defines whether the direction of the audio object sufficiently corresponds to the direction of the subframes and subbands of the frame.

[0020] According to an embodiment, the apparatus further comprises means for skipping encoding the first audio direction parameter value as a quantized first audio direction parameter value in response to the masking parameter indicating that the direction of the audio object substantially corresponds to the direction of the subframe and the subband of the frame.

[0021] According to an embodiment, the apparatus further comprises means for adjusting the masking parameter by a weighting function, the weighting function adjusting the direction of the audio object to a required angle to sufficiently correspond to the directions of the sub-frame and the sub-band of the frame.

[0022] According to an embodiment, the apparatus further comprises means for encoding in or with the bitstream an indication for indicating whether skipping encoding of the first parameter value as the quantized first parameter value is allowed.

[0023] According to an embodiment, the indication is audio frame specific.

[0024] According to an embodiment, the means for determining a bit efficient encoding for the first audio direction parameter value comprises means for using a second audio direction parameter value of at least one audio object as reference when encoding the first audio direction parameter value as a quantized first audio direction parameter value.

[0025] According to an embodiment, the device further includes a component for performing the following operations: estimating the number of bits required to encode the first audio direction parameter value as a quantized first audio direction parameter value; calculating, for each object, the angular difference between the first audio direction parameter value for all time-frequency tiles and the quantized direction of the object; estimating the number of bits required to encode the angular difference; in response to the number of bits required to encode the angular difference being less than the number of bits required to encode the first audio direction parameter value as the quantized first audio direction parameter value, indexing the object as a reference object; and among the objects indexed as reference objects, selecting the object with the least number of bits required to encode the angular difference as the reference object to be used.

[0026] According to an embodiment, the apparatus further comprises means for: signalling if the reference object is used for encoding; and if agreed, including an indication of an index of the reference object in or along with the bitstream to be encoded.

[0027] According to an embodiment, the apparatus further comprises means for signaling the usage of the reference object and the index of the reference object as being specific to the time-frequency tile.

[0028] According to a second aspect, a method comprises: obtaining a first audio direction parameter value for each subband of a subframe of a frame of an audio signal; obtaining a second audio direction parameter value for the subframe of the frame of the audio signal for one or more audio objects associated with the audio signal; and determining a bit-efficient encoding for each first audio direction parameter value of the subframe based on a similarity between the first audio direction parameter value for each subband and the second audio direction parameter values ​​for the one or more audio objects.

[0029] According to a third aspect, a device comprises at least one processor and at least one memory, wherein the at least one memory has computer program code stored thereon, and the at least one memory and the computer program code are configured to, together with the at least one processor, cause the device to at least perform: obtaining a first audio direction parameter value for each subband of a subframe of a frame of an audio signal; obtaining a second audio direction parameter value for the subframe of the frame of the audio signal for one or more audio objects associated with the audio signal; and determining a bit-efficient encoding for each first audio direction parameter value for the subframe based on a similarity between the first audio direction parameter value for each subband and the second audio direction parameter value for the one or more audio objects.

[0030] According to other aspects, a computer-readable storage medium includes code for use by an apparatus that, when executed by a processor, causes the apparatus to perform the above-described method. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] For a more complete understanding of example embodiments, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0032] Figure 1 schematically illustrates a system suitable for implementing the apparatus of some embodiments;

[0033] Figure 2 schematically illustrates a metadata encoder according to some embodiments;

[0034] Figure 3 A flow chart for encoding a time-frequency tile of an audio frame according to an embodiment is shown;

[0035] Figure 4 A flowchart for encoding a time-frequency tile of an audio frame according to another embodiment is shown;

[0036] Figure 5 An example of selecting encoding of a time-frequency tile between normal encoding and audio object indexing according to an embodiment is shown;

[0037] Figure 6An example of indicating encoding of a time-frequency tile between normal encoding and an audio object index according to an embodiment is shown;

[0038] Figure 7 A flowchart for encoding a time-frequency tile of an audio frame according to yet another embodiment is shown;

[0039] Figure 8a , Figure 8b An example of a weighting function for defining candidate pairs of time-frequency tiles and audio objects according to an embodiment is shown;

[0040] Fig. 9 An example of indicating encoding of a time-frequency tile between normal encoding and skip encoding according to an embodiment is shown;

[0041] Fig.10 An example of indicating encoding of a time-frequency tile between normal encoding, audio object indexing, and skip encoding according to an embodiment is shown;

[0042] Fig.11 A flowchart for encoding a time-frequency tile of an audio frame according to yet another embodiment is shown;

[0043] Fig.12 Example electronic devices are shown that can be used to implement embodiments. DETAILED DESCRIPTION

[0044] Suitable devices and possible mechanisms for providing metadata parameters derived from effective spatial analysis are described in more detail below. In the following discussion, multi-channel systems will be discussed with respect to multi-channel microphone implementations. However, as described above, the input format can be any suitable input format, such as multi-channel speakers, Ambisonics (FOA / HOA), etc. It should be understood that in some embodiments, the channel position is based on the position of the microphone, or is based on a virtual position or direction. In addition, the output of the example system is a multi-channel speaker arrangement. However, it should be understood that the output can be rendered to the user via means other than speakers. In addition, the multi-channel speaker signal can be translated to be summarized as two or more playback audio signals.

[0045] As discussed previously, spatial metadata parameters in frequency bands such as directional and direct-to-total energy ratio (or diffuseness-ratio, absolute energies, or any suitable representation indicating the directionality / non-directionality of sound at a given time-frequency interval) parameters are particularly suitable for representing the perceptual characteristics of a natural sound field. Synthetic sound scenes such as 5.1 speaker mixes often utilize audio effects and amplitude panning methods that provide spatial sounds that are different from those occurring in a natural sound field. In particular, a 5.1 or 7.1 mix may be configured so that it contains coherent sounds played from multiple directions. For example, some sounds of a 5.1 mix that are typically perceived directly in front are not produced by the center (channel) speaker, but are coherently produced, for example, from the left and right front (channel) speakers, and possibly also from the center (channel) speaker. Spatial metadata parameters such as directional and energy ratios do not accurately represent such spatial coherence characteristics. Therefore, other metadata parameters such as coherence parameters may be determined from analysis of the audio signal to represent the audio signal relationships between channels.

[0046] In addition to the multi-channel input format audio signal, the encoding system may also be required to encode audio objects representing various sound sources within the physical space. Whether it is in the form of metadata or some other mechanism, each audio object may be accompanied by directional data in the form of azimuth and elevation values ​​that indicate the location of the audio object within the physical space.

[0047] As described above, an example of incorporating directional information of an audio object into metadata is using the determined azimuth and elevation values.

[0048] A directional parameter of the audio object may be determined and indexed based on the actual sphere-covered based directional distribution in order to define a more uniform directional distribution.

[0049] Furthermore, the proposed directional index for audio objects can be used with downmix signals ('channels') to define a parameterized immersive format that can be used, for example, in the Immersive Voice and Audio Services (IVAS) codec. Alternatively and additionally, a spherical grid format can be used in the codec to quantize directions.

[0050] about Figure 1 , shows an example device and system for implementing an embodiment of the present application. The system 100 is shown as having an 'analysis' part 121 and a 'synthesis' part 131. The 'analysis' part 121 is the part from receiving a multi-channel loudspeaker signal to encoding of metadata and downmix signals, while the 'synthesis' part 131 is the part from decoding of the encoded metadata and downmix signals to rendering of the regenerated signal (e.g. in the form of a multi-channel loudspeaker).

[0051] The input to the system 100 and the 'analysis' portion 121 is a multi-channel signal 102. A microphone channel signal input is described in the following example, however, in other embodiments, any suitable input (or synthesized multi-channel) format may be implemented. For example, in some embodiments, the spatial analyzer and spatial analysis may be implemented external to the encoder. For example, in some embodiments, spatial metadata associated with the audio signal may be provided to the encoder as a separate bitstream. In some embodiments, the spatial metadata may be provided as a set of spatial (directional) index values.

[0052] The multi-channel signal is passed to a down-mixer 103 (also called a “transmission signal generator”) and an analysis processor 105 .

[0053] In some embodiments, down mixer 103 is configured to receive a multi-channel signal, down-mix the signal to a determined number of channels, and output a down-mix signal 104 (also referred to as a "transmission signal"). For example, down mixer 103 can be configured to generate a 2-audio channel down-mix of the multi-channel signal. The determined number of channels can be any suitable number of channels. In some embodiments, down mixer 103 is optional, and the multi-channel signal is passed to encoder 107 unprocessed in the same manner as the down-mix signal in this example.

[0054] In some embodiments, the analysis processor 105 is further configured to receive the multichannel signals and analyze these signals to generate metadata 106 associated with the multichannel signals and thus associated with the downmix signal 104. The analysis processor 105 may be configured to generate metadata that may include, for each time-frequency analysis interval, a direction parameter 108, an energy ratio parameter 110 (and in some embodiments, a coherence parameter 112) and a diffuseness parameter. In some embodiments, the direction, energy ratio and diffuseness parameters may be considered spatial audio parameters. In other words, the spatial audio parameters include parameters intended to characterize the sound field created by the multichannel signal (or generally two or more playback audio signals).

[0055] In some embodiments, the parameters generated may differ from band to band. Thus, for example, in band X, all parameters are generated and sent, while in band Y, only one of the parameters is generated and sent, and further, in band Z, no parameters are generated or sent. A practical example of this may be that for some bands, such as the highest frequency band, certain parameters are not required for perceptual reasons. The downmix signal 104 and the metadata 106 may be passed to an encoder 107.

[0056] The encoder 107 may include an audio encoder core 109 configured to receive the downmix (or other) signals 104 and generate suitable encodings of these audio signals. In some embodiments, the encoder 107 may be a computer (running suitable software stored on a memory and on at least one processor), or alternatively may be a specific device, such as using an FPGA or ASIC. The encoding may be implemented using any suitable scheme.

[0057] In addition, the encoder 107 may include a metadata encoder / quantizer 111 configured to receive metadata and output information in an encoded or compressed form. The metadata encoder / quantizer 111 may include an energy ratio analyzer (or quantization resolution determiner). The energy ratio analyzer may be configured to receive the energy ratio and generate a quantization resolution for the directional parameters for all time-frequency tiles in the frame based on the analysis (in other words, a quantization resolution for the elevation and azimuth values). This bit allocation may be defined, for example, by bits_dir0[0:N-1][0:M-1].

[0058] The metadata encoder / quantizer 111 may include a direction index generator configured to receive a direction parameter 108 (such as an azimuth angle and elevation angle θ(k,n)) and quantization bit allocation, and a quantized output is generated therefrom. The quantization may be based on an arrangement of spheres (forming a spherical grid arranged in a ring on a 'surface' sphere), which is defined by a lookup table defined by a determined quantization resolution. In other words, the spherical grid uses the concept of covering a sphere with smaller spheres, and considering the centers of the smaller spheres as points defining a grid of nearly equidistant directions. The smaller spheres thus define cones or solid angles about the center point, which may be indexed according to any suitable indexing algorithm. Although spherical quantization is described herein, any other suitable quantization (linear or non-linear) may also be used.

[0059] For example, the lookup table may allocate 1-11 bits for directional parameters (azimuth and elevation) based on, for example, an energy ratio index. Depending on the number of bits allocated, a certain number of elevation values ​​in the 'northern hemisphere' of the directional sphere (including the equator) and the number of azimuth values ​​at each elevation for each quantizer are defined.

[0060] For example, for 5 bits, there may be 4 elevation values ​​corresponding to [0, 30, 60, 90] and 4-1=3 negative elevation values ​​[-30, -60, -90]. For the first elevation value 0, there may be 12 equidistant azimuth values, for elevation values ​​30 and -30, there may be 7 equidistant azimuth values, and so on.

[0061] In some embodiments, Figure 1The encoder 107 may further interleave, multiplex into a single data stream or embed metadata into the encoded downmix signal before transmission or storage as indicated by the dashed line in FIG. Multiplexing may be achieved using any suitable scheme.

[0062] On the decoder side, the received or acquired data (stream) may be received by a decoder / demultiplexer 133. The decoder / demultiplexer 133 may demultiplex the encoded stream and pass the audio encoded stream to a downmix extractor 135 configured to decode the audio signal to obtain a downmix signal. Similarly, the decoder / demultiplexer 133 may include a metadata extractor 137 configured to receive the encoded metadata and generate the metadata. In some embodiments, the decoder / demultiplexer 133 may be a computer (running suitable software stored on a memory and on at least one processor), or alternatively may be a specific device, for example using an FPGA or ASIC.

[0063] The decoded metadata and downmix audio signal may be passed to a synthesis processor 139. The 'synthesis' portion 131 of the system 100 further illustrates a synthesis processor 139 configured to receive the downmix and metadata and to recreate synthesized spatial audio in the form of a multichannel signal 110 in any suitable format based on the downmix signal and the metadata (which may be a multichannel speaker format, or in some embodiments any suitable output format such as a binaural or Ambisonics signal, depending on the use case).

[0064] The additional input 120 may specifically include directional data associated with a plurality of audio objects. A specific example of such a use case is a teleconference scenario, where participants are positioned around a table. Each audio object may represent audio data associated with each participant. In particular, the audio object may have position data associated with each participant.

[0065] Thus, the system 100 can be configured to accept multiple audio objects along the input 120, and each audio object can have associated directional data. In turn, the audio objects including the associated directional data can be passed to the audio object encoder 121 for encoding and quantization. In this regard, the directional data associated with each audio object can also be represented in terms of an azimuth angle φ and an elevation angle θ, wherein the azimuth value and the elevation value of each audio object indicate the position of the object in space at any point in time. The azimuth and elevation values ​​can be updated on a time frame-by-time frame basis, which is not necessarily consistent with the time frame resolution of the directional metadata parameters associated with the multi-channel audio signal.

[0066] Typically, the directional information of the N active input audio objects to the audio object encoder 121 can be expressed as P q =(θq ,φ q ),q=0:N-1, where P q is the directional information of the audio object with index q, which has a two-dimensional vector including an elevation angle θ value and an azimuth angle φ value.

[0067] For a more detailed explanation of how to find the vector difference between the directional information of an audio object and the "template" audio directional parameters derived for the audio object, and then quantize the vector difference using a spherical quantization scheme, refer to Figure 2 Some functions of the audio object encoder 121 are described in more detail.

[0068] The audio object encoder 121 may include an audio object direction deriver 201 that is arranged to derive a suitable "template" audio direction parameter for each audio object. In an embodiment, this may be derived as an N-dimensional vector having N derived audio direction parameters corresponding to the N audio objects as elements. These derived audio direction parameters may be derived from the perspective of considering the circumferential distribution of the audio objects around a circle. In particular, the derived audio direction parameters may be considered from the perspective of the audio object directions being uniformly distributed as N equidistant points around a unit circle.

[0069] In the following description, N derived audio direction parameters are disclosed as forming a vector structure (referred to as vector SP), wherein each element corresponds to a derived audio direction parameter for one of the N audio objects. However, it should be understood that the following disclosure can be applied by considering the derived audio direction parameters as a collection of indexed parameters that do not need to be constructed in the form of a vector.

[0070] The audio object direction exporter 201 may be configured to export a "template" derived audio direction vector SP having N two-dimensional elements, whereby each element represents an azimuth and an elevation angle associated with an audio object. Furthermore, the vector SP may be initialized by setting the azimuth and elevation values ​​of each element so that the N audio objects are evenly distributed around a unit circle. This may be accomplished by initializing each audio object direction element within the vector to have an elevation value of "zero" and an azimuth value of is implemented as, where q is the index of the associated audio object. Therefore, for N audio objects, the vector SP can be written as:

[0071]

[0072] In other words, the SP vector can be initialized so that the directional information (derived audio direction parameter) of each audio object is assumed to be along the unit circle from the azimuth value 0 to 0 Start distributing it evenly.

[0073] In turn, a derived audio direction SP vector having elements including derived audio direction parameters corresponding to audio objects may be passed to an audio direction rotator 203 in the audio object encoder 121. The audio direction rotator 203 is also depicted as receiving an audio object 120. In particular, by rotating each derived direction within the SP vector by the azimuth value of the first component φ0 from the first received audio object P0, the audio direction rotator 203 may then use the audio direction parameters of the first audio object in subsequent processing. That is, each azimuth component of each derived audio direction parameter within the derived vector SP may be rotated by adding the value of the first azimuth component φ0 of the first received audio object. In terms of the SP vector, this operation results in each element having the following form:

[0074]

[0075] For embodiments arranged to derive the audio direction vector SP with an elevation angle of "zero", the vector SP may be derived solely from the azimuth angle To represent, where φi is given by Given the rotated azimuth component, SP is the rotated derived audio direction vector. As a result of this step, the rotated derived audio direction vector Now align with the direction of the first audio object on the unit circle.

[0076] Furthermore, the audio object encoder 121 may be configured to quantize and encode the rotated derived audio direction vector In an embodiment, this may simply include quantizing the rotation angle φ0 to a certain resolution by the quantizer 211. For example, a linear quantizer with a 2.5 degree resolution (that is, 5 degrees between consecutive points on the linear scale) results in 72 linear quantization levels. Note that the (unrotated) derived audio direction vector SP depends on the number of active audio objects N, and this factor may be passed to the decoder or otherwise agreed upon with the encoder.

[0077] The audio object encoder 121 may also include an audio direction relocator & indexer 205 configured to reorder the positions of the received audio objects to more closely align with the rotated derived audio direction vector The rotated derived audio direction of the elements of . This can be done by reordering the positions of the audio objects so that the azimuth value of each reordered audio object is consistent with the vector The reordered position of each audio object can be encoded as a permutation index.

[0078] K bits (which may be referred to as I φ0 ) and an index I representing the index order of the audio direction parameters of audio objects 1 to N-1 ro May form part of an encoded bitstream such as from encoder 100 .

[0079] As described above, the rotated derived audio direction vector may be a "template" from which an audio direction difference vector may be derived for the audio direction parameter of each audio object. This may be determined, for example, by Figure 2 In an embodiment, the audio direction difference vector may be a two-dimensional vector having an elevation difference value and an azimuth difference value. q ,,φ q ) of the audio object P q The audio direction difference vector (Δθ q ,,Δφ q ) can be found as (Δθ q ,,

[0080] It should be understood that the audio object P q The directional difference is based on the rotated derived audio direction vector The difference between each element and the corresponding reordered (or repositioned) audio object is formed.

[0081] In turn, the directional difference vector (Δθ ) associated with each audio object may be quantized by the spherical quantizer & indexer 209. q ,Δφ q ) for quantification.

[0082] The above audio coding scheme can also be considered to be applicable to the 3GPP IVAS encoder and can be called Metadata Assisted Spatial Audio (MASA). Therein, directional parameters such as azimuth and elevation angles and energy ratios obtained by multi-channel analysis in the time-frequency domain can be considered to represent spatial metadata. On the other hand, the directional metadata of each audio object is processed in a separate processing chain, such as Figure 1 and Figure 2 as shown in .

[0083] Obviously, metadata describing the direction / position of individual audio objects on the one hand, and metadata describing spatial audio within the same audio scene on the other hand, contain certain similarities and correlations. A certain number of bits are required to represent the compressed / quantized spatial metadata associated with the spatial audio. Similarly, a certain number of bits are required for metadata associated with any audio object that is to be encoded together with the spatial audio. However, if the compression / quantization of these two types of metadata is performed separately, the synergy of metadata quantization of these two types of metadata is not exploited.

[0084] In the following, an enhanced method for encoding time-frequency tiles of an audio frame will be described in more detail according to various embodiments.

[0085] exist Figure 3 The method disclosed in the disclosure includes: obtaining (300) a first audio direction parameter value for each subband of a subframe of a frame of an audio signal; obtaining (302) a second audio direction parameter value for the subframe of the frame of the audio signal for one or more audio objects associated with the audio signal; and determining (304) a bit-efficient encoding for each first audio direction parameter value of the subframe based on a similarity between the first audio direction parameter value for each subband and the second audio direction parameter values ​​for the one or more audio objects.

[0086] Thus, the method provides encoding of directional information for a MASA time-frequency map tile, wherein audio object directional metadata is also obtained, and a frame-wise comparison of at least the MASA directional metadata with the directional metadata of the audio object signal is performed. As a result of the comparison, the most bit-efficient way of encoding the directional metadata is determined for a frame or a portion of a frame (such as a subframe or a time-frequency map tile).

[0087] According to an embodiment, the first and second audio direction parameters are defined as points on the surface of a sphere. Thus, the audio direction parameter may be defined, for example, as a direction vector whose value is defined in three dimensions, or as an index value defining a direction from the center of a sphere to a position on the surface of the sphere.

[0088] According to an embodiment, the first audio direction parameter value comprises at least one azimuth value and at least one elevation value for each subband and subframe, and the second audio direction parameter value comprises at least one azimuth value and at least one elevation value for each audio object for each subframe.

[0089] Thus, as explained above, in the MASA audio coding scheme, directional parameters are typically defined as azimuth and elevation values, and this also applies to audio object direction parameters. Note that for first audio direction parameter values ​​(such as the parameterized spatial audio-related arrival direction parameters used in MASA), the azimuth and elevation values ​​can be defined in both the time domain and the frequency domain, whereas for second audio direction parameter values ​​(such as the audio object directional parameters), it is sufficient to define them only in the time domain (such as associated with a frame of the audio signal or a subframe of a frame).

[0090] Hereinafter, the “first audio direction parameter value” and the “second audio direction parameter value” are simply referred to as the “first parameter value” and the “second parameter value”.

[0091] According to an embodiment, the bit-efficient encoding for the first parameter value includes: in response to the similarity between the second parameter value of the audio object and the first parameter value being lower than a predetermined threshold, encoding the index of the audio object as the first parameter value; or in response to the similarity between the second parameter value of the audio object and the first parameter value being higher than the predetermined threshold, encoding the first parameter value as a quantized first parameter value.

[0092] Thus, depending on the direction metadata, the frequency map tile direction may be encoded as a pointer / index to an audio object (thus using the direction of the audio object itself), or separately encoded as a quantized frequency map tile direction parameter.

[0093] According to an embodiment, a possible masking of a time-frequency map tile by an audio object is determined based on the audio signal energies of the time-frequency map tile and the audio object for a candidate time-frequency map tile / audio object pair.

[0094] According to an embodiment, when an audio object masks a frequency map tile, the frequency map tile direction may be completely omitted from the encoding. In yet another embodiment, encoding of the audio object metadata may be skipped if the audio object metadata is masked by MASA audio.

[0095] According to an embodiment, which may be used with or independently of other embodiments, the bit-efficient encoding for the first parameter value comprises using a second parameter value of at least one audio object as a reference when encoding the first parameter as the quantized first parameter value.

[0096] These embodiments are described in more detail in the following examples.

[0097] Figure 4 A flow chart according to an embodiment is shown, wherein the most bit-efficient way of encoding the directional metadata of the time-frequency image block is selected between the directional difference between the original directional parameters and the quantized directional parameters of the index or coded time-frequency image block of the audio object. Figure 3 The steps are similar to those in : first, directional metadata (ie, azimuth, elevation) for the time-frequency tile is obtained ( 400 ), and second, directional metadata is obtained for all audio objects ( 402 ).

[0098] The embodiment further includes: determining, for each subband and subframe, a directional difference between an original first parameter value and a quantized first parameter value (404); determining, for each subband and subframe, a directional difference between an original first parameter value and a second parameter value of the audio object (406); determining a minimum value of the directional difference between the original first parameter value and the second parameter value of the audio object (408); and using the minimum value in a similarity comparison between the first parameter value and the second parameter value (410).

[0099] The directional difference between the original directional parameters and the quantized directional parameters of the time-frequency tile can be determined as follows:

[0100] The original direction of the time-frequency tile (azimuth, elevation) Instead of the direction after the above directional data quantization The difference in direction between the two (the so-called great circle distance) d oa According to equation 1 it is calculated as:

[0101]

[0102] In the following, according to Figure 1 and Figure 2 The MASA directional data encoding described is called "normal encoding". The directional differences (d oai , i=0...N audio objects). Then, these directional differences are compared to find the minimum directional difference between the time-frequency image block and one of the audio objects.

[0103] According to an embodiment, if the minimum direction difference is less than a predetermined threshold T, the time-frequency map tile direction is encoded as an audio object index, otherwise "normal encoding" is used. In other words, if the time-frequency map tile direction is close enough to the direction of the audio object, they can be considered consistent and the time-frequency map tile direction can be simply encoded as an audio object index.

[0104] According to an embodiment, if the minimum directional difference corresponds to an audio object, the time-frequency map tile direction is encoded as an audio object index, otherwise "normal encoding" is used. Therefore, compared with the previous embodiment, the predetermined threshold T=0, where a stricter rule requires that the time-frequency map tile direction should be completely consistent with the direction of the audio object, so that the time-frequency map tile direction is simply encoded as an audio object index.

[0105] pass Figure 5 The above embodiment is illustrated by an example of , where the azimuth plane of a sphere is shown to be divided into 16 directional quantization steps. Note that in actual practice elevation values ​​are also considered, but in this paper only azimuth is considered for illustrative purposes.

[0106] Figure 5 Seven time-frequency plot tiles 501-507 along the circumference of the azimuth plane are shown. There are also five quantized directions 511-515 along the circumference of the azimuth plane at lines representing direction quantization steps. Figure 5 The positions of two audio objects i and j in the azimuth plane are also shown. Time-frequency map blocks 501, 504, 505 and 507 are quantized to the closest quantized directions 511, 512, 513, 515, respectively. However, time-frequency map blocks 502, 503 and 506 are respectively located in directions that are close enough to the directions of audio objects i and j. In other words, time-frequency map blocks 502, 503 and 506 are considered to be masked by audio objects i and j, respectively. Therefore, instead of encoding the quantized direction metadata of time-frequency map blocks 502 and 503, the index of audio object i can be encoded. Similarly, for time-frequency map block 506, the index of audio object j can be encoded.

[0107] As mentioned above, the time-frequency direction is encoded using a variable bitrate, where 1-11 bits per time-frequency tile are used in the encoding, depending on the energy ratio. When using the index of audio objects, the number of bits required to encode the direction depends on the number of audio objects. Therefore, for a single time-frequency tile, either approach can be better in terms of bitrate.

[0108] According to an embodiment, an indication is encoded in the bitstream to indicate whether the direction of the time-frequency map tile can be encoded as an index of an audio object. Since the direction can be encoded as an index of an audio object or quantized normally, an additional bit can be added to the bitstream for each time-frequency block to indicate which one is being used. Due to changing circumstances, in some cases it may be beneficial to use encoding as an index of an audio object, while in some cases it may be beneficial to use normal encoding. Thus, for example, an additional bit may be used at the frame level to indicate whether normal encoding is used or whether the direction of the time-frequency map tile can be encoded as an index of an audio object.

[0109] pass Figure 6 This is illustrated by an example of, where a sequence of audio frames n, n+1, n+2, ... is shown. Each audio frame with a time length of 20 ms is divided into four subframes with a time length of 5 ms. In the frequency domain, each audio frame is further divided into multiple frequency subbands. Therefore, each frame is represented by multiple time-frequency tiles. In this example, there are two audio objects 0 and 1, both of which have audio object direction metadata defined for each audio frame n, n+1, n+2.

[0110] Each audio frame n, n+1, n+2 is provided with a further bit indicating whether an audio object reference is possible; i.e., it indicates whether the time-frequency tile direction within the frame in question can be encoded as an audio object index. In frames n and n+2, this bit is set to 0, while in frame n+1, this bit is set to 1. Therefore, in frame n+1, any of these time-frequency tiles can be encoded as an audio object index (brighter tiles) or encoded normally (darker tiles). In this paper, the determination of whether the use of audio object indexes is allowed (by setting this bit to 1) is performed from the perspective of improving compression efficiency, i.e., whether it is better to encode the time-frequency tile direction as an index of the audio object or to encode it according to the normal coding scheme in terms of reducing the bit rate of the encoded bitstream.

[0111] Figure 7 A flow chart according to an embodiment is shown, wherein possible masking of a time-frequency tile by an audio object is determined based on the audio signal energies of the time-frequency tile and the audio object for the candidate time-frequency tile and the time-frequency tile-audio object pair. Figure 3 The steps are similar to those in : first, obtain directional metadata (ie, azimuth, elevation) for the time-frequency tile ( 700 ), and second, obtain directional metadata for all audio objects ( 702 ).

[0112] The embodiment further includes determining a masking parameter based on the signal energy values ​​for the subframe and the subband and the signal energy value of the audio object for the subframe, the masking parameter defining whether the direction of the audio object sufficiently corresponds to the direction of the subframe and the subband of the frame (704).

[0113] Furthermore, in addition to the directional metadata, the signal energies corresponding to the time-frequency map blocks and audio objects are considered by calculating the audio signal energies of the time-frequency map blocks and audio objects for the candidate time-frequency map block / audio object pairs. Here, for example, the following equation 2 can be used:

[0114]

[0115] Where M is the masking parameter for the candidate time-frequency patch / audio object pair, E(s a ) is the signal energy corresponding to the time-frequency block, r a is the energy ratio of the time-frequency image block, E(s b ) is the energy of the audio signal associated with the audio object (which may be band-limited to a subband of the time-frequency tile), d ab is the great circle distance between the time-frequency image patch direction and the audio object direction (defined in Equation 1 above), and W is a weighting function used to define candidate pairs of time-frequency image patches and audio objects, as explained below.

[0116] Furthermore, the directional encoding of the time-frequency tile is controlled according to the masking parameters, ie, based on the signal energy and directional metadata of the time-frequency tile and the audio object pair.

[0117] According to an embodiment, in response to the masking parameter indicating that the direction of the audio object sufficiently corresponds to the direction of the subframe and the subband of the frame, the encoding is controlled to skip encoding the first parameter value as a quantized first parameter value (706).

[0118] Based on the masking parameter M, the encoding can be controlled as follows:

[0119] - If M > 1, the time-frequency tile is considered to be masked by the audio object and thus the direction encoding of the time-frequency tile is skipped;

[0120] - If M = < 1, normal direction encoding is used.

[0121] The skip direction coding can be indicated by 1 bit.

[0122] The weighting function W is used only when the audio object and the time-frequency patch have sufficiently similar directions to allow masking to occur. Various types of weighting functions can be used depending on the specific situation. Figure 8a and Figure 8b Two example weighting functions based on the great circle distance (d) between an audio object and a time-frequency patch are shown.

[0123] Figure 8a A weighting function with a mutation threshold of 0.0349 is shown, which corresponds to a 2 degree interval in azimuth when the elevation angle is 0. Therefore, for a pair of time-frequency tile and audio object separated by more than 2 degrees in azimuth, Equation 2 obtains the value "zero" and normal directional encoding is applied to the time-frequency tile.

[0124] Figure 8bA weighting function is shown that decreases linearly from 1 to 0 (at the value d = 0.1), which corresponds to a spacing of about 6 degrees in azimuth when the elevation angle is 0. Therefore, for a pair of time-frequency tile and audio object that is separated by more than 6 degrees in azimuth, Equation 2 obtains the value "zero" and normal directional coding is applied to the time-frequency tile. On the other hand, if the spacing is, for example, 4 degrees in azimuth, directional coding of the time-frequency tile can be skipped depending on the signal energy and energy ratio of the time-frequency tile.

[0125] According to an embodiment, an indication is encoded in the bitstream to indicate whether directional encoding of a time-frequency map tile can be skipped. Due to varying circumstances, in some cases it may be beneficial to skip directional encoding of a time-frequency map tile, while in some cases it may be beneficial to use normal encoding. Thus, for example, an additional bit may be used at the frame level to indicate whether normal encoding is used or whether skipping directional encoding of a time-frequency map tile is allowed.

[0126] pass Fig. 9 This is illustrated by the example of Figure 6 Similarly, a sequence of audio frames n, n+1, n+2, ... is shown. Each audio frame with a time length of 20 ms is divided into four subframes with a time length of 5 ms. In the frequency domain, each audio frame is further divided into multiple frequency subbands. This results in multiple time-frequency tiles for each frame. Likewise, there are two audio objects 0 and 1, both of which have audio object direction metadata defined for each audio frame n, n+1, n+2.

[0127] Each audio frame n, n+1, n+2 is provided with another bit indicating whether it is allowed to skip the directional encoding of the time-frequency tiles in the frame. In frames n and n+2, the bit is set to 0, while in frame n+1, the bit is set to 1. Therefore, in frame n+1, the directional encoding of any of these time-frequency tiles can be skipped (brighter tiles) or the directional encoding can be performed normally (darker tiles). In this article, determining whether it is allowed to skip the directional encoding of any of the time-frequency tiles (by setting the bit to 1) is performed from the perspective of improving compression efficiency, that is, in terms of reducing the bit rate of the encoded bitstream, which one is better, skipping the directional encoding of any of the time-frequency tiles in the frame or applying the normal encoding scheme.

[0128] According to an embodiment, the bitstream may include an indication for indicating whether the direction of the time-frequency map tile can be encoded as an index of the audio object and whether the direction encoding of the time-frequency map tile can be skipped. Therefore, the above two embodiments can be combined to apply to different frames of the audio frame sequence.

[0129] Fig.10 Shown with Figure 6 and Fig. 9 An example similar to the example in , where a frame level indication is included in the bitstream to indicate whether direction encoding is done in the normal way, whether audio object indexes can be used, or whether direction metadata can be skipped. Again, during encoding, the mode is selected based on which mode is most bit efficient.

[0130] In this article, the indication of the mode can be performed by two bits at the frame level included in the bitstream. Alternatively, only one bit can be used so that the absence of the bit indicates one mode (e.g., direction encoding will be performed in a normal manner), while the other two options are indicated by the value of the bit included in the bitstream.

[0131] In the above embodiments, the use of a threshold T or a weighting function W ensures that the time-frequency tile direction is close enough to the direction of the audio object. However, using only directional differences in control encoding may not always produce the best results for compression efficiency in terms of bit rate.

[0132] Fig.11 A flow chart for an embodiment is shown, wherein a second parameter value of at least one audio object is used as a reference when encoding a first parameter value as a quantized first parameter value. The starting point of the embodiment is Figure 3 , Figure 4 , Figure 7 The first two steps of any of the flowcharts in have been completed, ie, the directional metadata for the time-frequency tile and the directional metadata for all audio objects have been obtained.

[0133] This embodiment includes: estimating (1100) the number of bits required to encode a first parameter value as a quantized first parameter value; calculating (1102) for each object the angular difference between the first parameter value for all time-frequency blocks and the quantized direction of the object; estimating (1104) the number of bits required to encode the angular difference; in response to the number of bits required to encode the angular difference being less than the number of bits required to encode the first parameter value as the quantized first parameter value, indexing (1106) the object as a reference object; and among the objects indexed as reference objects, selecting (1108) the object with the least number of bits required to encode the angular difference as the reference object to be used.

[0134] Therefore, instead of applying the directional difference between the time-frequency map tile direction and the direction of the audio object as a parameter for controlling the encoding, the embodiment uses the determined savings in the encoding bit rate as a criterion for controlling the encoding. Thus, it is possible to select audio objects with a larger range of directional differences between the time-frequency map tile direction and the direction of the audio object (e.g., compared to the limit set by the threshold T or the weighting function W) as a trade-off for better compression efficiency.

[0135] Note that when estimating the number of bits required to encode the angular difference between the first parameter value and the quantized direction of the object for all time-frequency tiles, this encoding refers to "normal encoding" as described above, i.e., encoding the first parameter value as a quantized first parameter value.

[0136] According to an embodiment, the method further comprises: signaling if the reference object is used for encoding; and if agreed, including an indication of the index of the reference object in or along with the bitstream to be encoded.

[0137] Therefore, similar to the above-described embodiments, an additional bit indicating whether a reference object is used for encoding may be used, for example, at the frame level.In order to indicate the index of the reference object, the required number of further bits may be included at the frame level.

[0138] According to an embodiment, the signaling using the reference object and the index indicating the reference object are performed for each time-frequency map block. Therefore, the reference object can be considered separately for each time-frequency map block. If applied, the reference object signaling can be sent for each time-frequency map block, followed by the index of the reference object of the time-frequency map block.

[0139] Thus, embodiments as described herein enable reducing the bit rate of an encoded audio bitstream.These embodiments also enable selectively deciding the most bit efficient way to encode a time-frequency tile.

[0140] Fig.12 An example electronic device that can be used as an analysis (encoding) or synthesis (decoding) device is shown. The device can be any suitable electronic device or apparatus. For example, in some embodiments, the device 1400 is a mobile device, a user device, a tablet computer, a computer, an audio playback device, etc.

[0141] In some embodiments, device 1400 includes at least one processor or central processing unit 1407. Processor 1407 may be configured to execute various program codes, such as the methods described herein.

[0142] In some embodiments, the device 1400 includes a memory 1411. In some embodiments, at least one processor 1407 is coupled to the memory 1411. The memory 1411 can be any suitable storage component. In some embodiments, the memory 1411 includes a program code portion for storing program codes that can be implemented on the processor 1407. In addition, in some embodiments, the memory 1411 can also include a storage data portion for storing data (e.g., data that has been processed or will be processed according to the embodiments described herein). Whenever necessary, the processor 1407 can obtain the implementation program code stored in the program code portion and the data stored in the storage data portion via the memory-processor coupling.

[0143] In some embodiments, device 1400 includes a user interface 1405. In some embodiments, user interface 1405 may be coupled to processor 1407. In some embodiments, processor 1407 may control the operation of user interface 1405 and receive input from user interface 1405. In some embodiments, user interface 1405 may enable a user to input commands to device 1400, for example, via a keyboard. In some embodiments, user interface 1405 may enable a user to obtain information from device 1400. For example, user interface 1405 may include a display configured to display information from device 1400 to a user. In some embodiments, user interface 1405 may include a touch screen or touch interface that enables information to be input to device 1400 and also displays information to a user of device 1400. In some embodiments, user interface 1405 may be a user interface for communicating with a position determiner as described herein.

[0144] In some embodiments, the device 1400 includes an input / output port 1409. In some embodiments, the input / output port 1409 includes a transceiver. In such embodiments, the transceiver can be coupled to the processor 1407 and configured to enable communication with other devices or electronic devices, for example, via a wireless communication network. In some embodiments, the transceiver or any suitable transceiver or transmitter and / or receiver device can be configured to communicate with other electronic devices or devices via a wired or wired coupling.

[0145] The transceiver can communicate with other devices via any suitable known communication protocol. For example, in some embodiments, the transceiver or transceiver device can use a suitable universal mobile telecommunications system (UMTS) protocol, a wireless local area network (WLAN) protocol such as, for example, IEEE802.X, a suitable short-range radio frequency communication protocol such as Bluetooth, or an infrared data communication path (IRDA).

[0146] The transceiver input / output port 1409 may be configured to receive signals and, in some embodiments, determine parameters as described herein using the processor 1407 executing appropriate code. In addition, the device may generate appropriate downmix signals and parameter outputs to send to a synthesis device.

[0147] In some embodiments, the device 1400 may be used as at least part of a synthesis device. Thus, the input / output port 1409 may be configured to receive a downmix signal, and in some embodiments receive parameters determined at a capture device or processing device as described herein, and generate a suitable audio signal format output using a processor 1407 executing suitable code. The input / output port 1409 may be coupled to any suitable audio output, such as a multi-channel speaker system and / or headphones, etc.

[0148] According to one aspect of the present invention, an apparatus is configured to implement the method as described above, and possibly one or more embodiments related thereto. Fig.11 The device depicted in the figure comprises: a component for obtaining a first audio direction parameter value for each subband of a subframe of a frame of an audio signal; a component for obtaining a second audio direction parameter value for the subframe of the frame of the audio signal for one or more audio objects associated with the audio signal; and a component for determining a bit-efficient encoding for each first audio direction parameter value for the subframe based on a similarity between the first audio direction parameter value for each subband and the second audio direction parameter value for the one or more audio objects.

[0149] According to another aspect, an apparatus comprises at least one processor and at least one memory having computer program code stored thereon, the at least one memory and the computer program code being configured to, together with the at least one processor, cause the apparatus to at least perform: obtaining a first audio direction parameter value for each subband of a subframe of a frame of an audio signal; obtaining a second audio direction parameter value for the subframe of the frame of the audio signal for one or more audio objects associated with the audio signal; and determining a bit-efficient encoding for each first audio direction parameter value for the subframe based on a similarity between the first audio direction parameter value for each subband and the second audio direction parameter value for the one or more audio objects.

[0150] In the above, some embodiments have been described with reference to an encoder or encoding method, it is to be understood that the resulting bitstream and the decoder or decoding method may have corresponding elements. Similarly, if the example embodiments have been described with reference to a decoder, it is to be understood that the encoder may have a structure and / or computer program for generating a bitstream to be decoded by a decoder.

[0151] Generally, various embodiments of the present invention may be implemented in hardware or dedicated circuits, or any combination thereof. Although various aspects of the present invention may be illustrated and described as block diagrams or using some other graphical representations, it is well known that the blocks, devices, systems, techniques or methods described herein may be implemented in hardware, software, firmware, dedicated circuits or logic, general purpose hardware or controllers or other computing devices, or some combination thereof, as non-limiting examples.

[0152] Embodiments of the present invention may be practiced in various components such as integrated circuit modules. The design of integrated circuits is generally a highly automated process. Complex and powerful software tools are available to convert a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0153] Programs, such as those offered by Synopsys, Inc. of Mountain View, Calif., and Cadence Design, of San Jose, Calif., can automatically route conductors and position components on a semiconductor chip using well-established design rules and a library of pre-stored design modules. Once the design of a semiconductor circuit is complete, the resulting design in a standardized electronic format (e.g., Opus, GDSII, etc.) can be transmitted to a semiconductor manufacturing facility or "fab" for fabrication.

[0154] The foregoing description has provided a complete and useful description of exemplary embodiments of the present invention by way of exemplary and non-limiting examples. However, when read in conjunction with the accompanying drawings and the accompanying examples, various modifications and adaptations will become apparent to those skilled in the relevant art in view of the above description. However, all of these and similar modifications of the teachings of the present invention will still fall within the scope of the present invention.

Claims

1. An apparatus for spatial audio coding, comprising means for performing the following operations: Obtain a first audio direction parameter value, wherein, The first audio direction parameter value is an audio direction parameter value for a sub-band of a sub-frame of a frame of a multi-channel audio signal; obtaining a second audio direction parameter value, wherein the second audio direction parameter value is an audio direction parameter of an audio object associated with the frame or the subframe of the multi-channel audio signal; and Based on a directionality difference between the first audio direction parameter value and the second audio direction parameter value, a bit efficient encoding for the first audio direction parameter value is determined.

2. The device according to claim 1, wherein: The first audio direction parameter and the second audio direction parameter are each defined as a point on the surface of a sphere.

3. The device according to claim 1 or 2, wherein: The first audio direction parameter value comprises at least one azimuth value and at least one elevation value for the subband of the subframe of the frame of the multi-channel audio signal, and the second audio direction parameter value comprises at least one azimuth value and at least one elevation value for the audio object associated with the frame or the subframe of the multi-channel audio signal.

4. The device according to any one of claims 1 to 3, wherein: The bit efficient encoding for the first audio direction parameter value comprises: In response to the directionality difference between the second audio direction parameter value and the first audio direction parameter value being lower than a predetermined threshold, encoding the index of the audio object as a first audio direction parameter value; or In response to the directionality difference between the second audio direction parameter value and the first audio direction parameter value being above the predetermined threshold, encoding the first audio direction parameter value as a quantized first audio direction parameter value.

5. The device according to claim 4, wherein: The means for determining a bit efficient encoding for the first audio direction parameter value further comprises means for: determining a directionality difference between the first audio direction parameter value and a quantized first audio direction parameter value for the subband of the subframe of the frame of the multichannel audio signal; determining a directionality difference between the first audio direction parameter value and the second audio direction parameter value; determining a minimum value of the directionality difference between the first audio direction parameter value and the second audio direction parameter value; as well as The minimum value is used in a directionality difference comparison between the first audio direction parameter value and the second audio direction parameter value.

6. The apparatus of claim 1, further comprising means for performing the following operations: An indication is encoded in or along with the bitstream, the indication being used to indicate whether an index of an audio object is allowed to be encoded as the first audio direction parameter value.

7. The device according to claim 1, wherein: The first audio direction parameter value further comprises a signal energy value of the subband of the subframe of the frame of the multi-channel audio signal, and the second audio direction parameter value further comprises a signal energy value of the audio object associated with the frame or the subframe of the multi-channel audio signal; the apparatus further comprises a component for performing the following operations: A masking parameter is determined based on a signal energy value of the subband of the subframe of the frame of the multichannel audio signal and a signal energy value of the audio object associated with the frame or the subframe of the multichannel audio signal, the masking parameter defining whether the second audio direction parameter value sufficiently corresponds to the first audio direction parameter value.

8. The apparatus of claim 7, further comprising means for performing the following operations: In response to the masking parameter indicating that the second audio direction parameter value sufficiently corresponds to the first audio direction parameter value, encoding the first audio direction parameter value as a quantized first audio direction parameter value is skipped.

9. The apparatus of claim 7, further comprising means for performing the following operations: The masking parameter is adjusted by a weighting function that adjusts the angle required for the second audio direction parameter value to substantially correspond to the first audio direction parameter value.

10. The apparatus of claim 7, further comprising means for performing the following operations: An indication is encoded in or with the bitstream, the indication being used to indicate whether it is permitted to skip encoding the first audio direction parameter value as a quantized first audio direction parameter value.

11. The device according to claim 1, wherein: The means for determining the bit efficient encoding for the first audio direction parameter value comprises means for using the second audio direction parameter value as a reference when encoding the first audio direction parameter value as a quantized first audio direction parameter value.

12. A method for spatial audio coding, comprising: Obtaining a first audio direction parameter value, wherein the first audio direction parameter value is an audio direction parameter value for a sub-band of a sub-frame of a frame of a multi-channel audio signal; obtaining a second audio direction parameter value, wherein the second audio direction parameter value is an audio direction parameter of an audio object associated with the frame or the subframe of the multi-channel audio signal; and Based on a directionality difference between the first audio direction parameter value and the second audio direction parameter value, a bit efficient encoding for the first audio direction parameter value is determined.

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