Method and apparatus for encoding and decoding successive frames of an ambisonics representation of a 2- or 3-dimensional sound field
Representations of spatial audio scenes using higher-order Ambisonics HOA technology typically require a large number of coefficients per time instant. This data rate is too high for most practical applications that require real-time transmission of audio signals. According to the invention, the compression is carried out in spatial domain instead of HOA domain. The (N+1) 2 input HOA coefficients are transformed into (N+1) 2 equivalent signals in spatial domain, and the resulting (N+1) 2 time-domain signals are input to a bank of parallel perceptual codecs. At decoder side, the individual spatial-domain signals are decoded, and the spatial-domain coefficients are transformed back into HOA domain in order to recover the original HOA representation.
1. A method for carrying out an encoding on received successive frames of a higher-order Ambisonics representation of a 2- or 3-dimensional sound field, denoted as_HOA coefficients, said method comprising:
transforming a number of O=(N+1) 2 input HOA coefficients of a frame into a number of O spatial domain signals representing a regular distribution of reference points on a sphere, wherein N is an order of said input HOA coefficients and is greater or equal to 3, and each one of said O spatial domain signals represents a set of plane waves which come from associated directions in space;
encoding each one of said O spatial domain signals using perceptual compression encoding steps or stages, thereby using encoding parameters selected such that a coding error is inaudible; and
multiplexing the encoded spatial domain signals of the frame into a joint bit stream for providing improved lossy compression of HOA representations of audio scenes.
2. The method according to claim 1 , wherein a masking used in said perceptual compression encoding is a psycho-acoustic masking and is a combination of time-frequency masking and spatial masking.
3. The method according to claim 1 , wherein said transforming into O spatial domain signals is plane wave decomposition.
4. The method according to claim 1 , wherein said encoding of each of said O spatial domain signals corresponds to the MPEG-1 Audio Layer III or AAC or Dolby AC-3 standard.
5. An apparatus for carrying out an encoding on received successive frames of a higher order Ambisonics representation of a 2- or 3-dimensional sound field, denoted as HOA coefficients, said apparatus comprising:
a transformer configured to transform a number O=(N+1) 2 input HOA coefficients of a frame into a number of O spatial domain signals representing a regular distribution of reference points on a sphere, wherein N is an order of said input HOA coefficients and is greater or equal to 3, and each one of said spatial domain signals represents a set of plane waves which come from associated directions in space;
encoders configured to encode each one of said O spatial domain signals using perceptual compression encoding steps or stages, thereby using encoding parameters selected such that a coding error is inaudible; and
a hardware multiplexer configured to multiplex the encoded spatial domain signals of the frame into a joint bit stream for providing improved lossy compression of HOA representations of audio scenes.
6. The apparatus according to claim 5 , wherein a masking used in said perceptual compression encoding is a psycho-acoustic masking and is a combination of time-frequency masking and spatial masking.
7. The apparatus according to claim 5 , wherein said transformation is a plane wave decomposition.
8. The apparatus according to claim 5 , wherein said perceptual encoding corresponds to the MPEG-1 Audio Layer III or AAC or Dolby AC-3 standard.
9. A method for decoding received successive frames of a perceptual compression encoded higher-order Ambisonics representation of a 2- or 3-dimensional sound field, which was encoded according to claim 1 , said decoding comprising:
de-multiplexing a received joint bit stream into a number of O=(N+1) 2 perceptual compression encoded spatial domain signals;
decoding each one of said O encoded spatial domain signals into a corresponding decoded spatial domain signal using perceptual compression decoding steps or stages corresponding to a selected encoding type and using decoding parameters matching the encoding parameters, wherein said O decoded spatial domain signals represent a regular distribution of reference points on a sphere; and
transforming said O decoded spatial domain signals into O output HOA coefficients of a frame, wherein N is an order of said output HOA coefficients for providing improved lossy compression of HOA representations of audio scenes.
10. The method according to claim 9 , wherein said decoding of each one of said O encoded spatial domain signals corresponds to the MPEG-1 Audio Layer III or AAC or Dolby AC-3 standard.
11. An apparatus for decoding received successive frames of a perceptual compression encoded higher-order Ambisonics representation of a 2- or 3-dimensional sound field, which was encoded according to claim 1 , said apparatus comprising:
a hardware demultiplexer which demultiplexes a received joint bit stream into O=(N+1) 2 perceptual compression encoded spatial domain signals;
decoders which decode each one of said O encoded spatial domain signals into a corresponding decoded spatial domain signal using perceptual compression decoding steps or stages corresponding to a selected encoding type and using decoding parameters matching the encoding parameters, wherein said O decoded spatial domain signals represent a regular distribution of reference points on a sphere; and
a transformer transforming said O decoded spatial domain signals into O output HOA coefficients of a frame, wherein N is an order of said output HOA coefficients for providing improved lossy compression of HOA representations of audio scenes.
12. The apparatus according to claim 11 , wherein said decoding of each one of said O encoded spatial domain signals corresponds to the MPEG-1 Audio Layer III or AAC or Dolby AC-3 standard.
13. An apparatus for carrying out an encoding on received successive frames of a higher order Ambisonics representation of a 2- or 3-dimensional sound field, denoted as HOA coefficients, said apparatus comprising:
a means for transforming a number O=(N+1) 2 input HOA coefficients of a frame into a number of O spatial domain signals representing a regular distribution of reference points on a sphere, wherein N is an order of said input HOA coefficients and is greater or equal to 3, and each one of said spatial domain signals represents a set of plane waves which come from associated directions in space;
a means for encoding each one of said O spatial domain signals using perceptual compression encoding steps or stages, thereby using encoding parameters selected such that a coding error is inaudible; and
a means for multiplexing the encoded spatial domain signals of the frame into a joint bit stream for providing improved lossy compression of HOA representations of audio scenes.
14. The apparatus according to claim 13 , wherein a means for masking used in said perceptual compression encoding is a psycho-acoustic masking and is a combination of time-frequency masking and spatial masking.
15. The apparatus according to claim 13 , wherein said means for transforming is a plane wave decomposition.
16. The apparatus according to claim 13 , wherein a means for said perceptual compression encoding corresponds to the MPEG-1 Audio Layer III or AAC or Dolby AC-3 standard.
17. An apparatus for decoding received successive frames of a perceptual compression encoded higher-order Ambisonics representation of a 2- or 3-dimensional sound field, which was encoded according to claim 1 , said apparatus comprising:
a means for demultiplexing a received joint bit stream into O=(N+1) 2 perceptual compression encoded spatial domain signals;
a means for decoding each one of said O encoded spatial domain signals into a corresponding decoded spatial domain signal using perceptual compression decoding steps or stages corresponding to a selected encoding type and using decoding parameters matching the encoding parameters, wherein said O decoded spatial domain signals represent a regular distribution of reference points on a sphere; and
a means for transforming said O decoded spatial domain signals into O output HOA coefficients of a frame, wherein N is an order of said output HOA coefficients for providing improved lossy compression of HOA representations of audio scenes.
18. The apparatus according to claim 17 , wherein said means for decoding of each one of said O encoded spatial domain signals corresponds to the MPEG-1 Audio Layer III or AAC or Dolby AC-3 standard.