Technique for encoding/decoding of codebook indices for quantized MDCT spectrum in scalable speech and audio codecs
Codebook indices for a scalable speech and audio codec may be efficiently encoded based on anticipated probability distributions for such codebook indices. A residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer may be obtained, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal. The residual signal may be transformed at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum. The transform spectrum is divided into a plurality of spectral bands, where each spectral band having a plurality of spectral lines. A plurality of different codebooks are then selected for encoding the spectral bands, where each codebook is associated with a codebook index. A plurality of codebook indices associated with the selected codebooks are then encoded together to obtain a descriptor code that more compactly represents the codebook indices.
1. A method for encoding in a scalable speech and audio codec, comprising:
obtaining a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal;
transforming the residual signal at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum;
dividing the transform spectrum into a plurality of spectral bands, each spectral band having a plurality of spectral lines;
selecting a plurality of different codebooks for encoding the spectral bands, where the codebooks have associated codebook indices;
performing vector quantization on spectral lines in each spectral band using the selected codebooks to obtain vector quantized indices;
encoding the codebook indices, wherein encoding the codebooks indices includes encoding at least two adjacent spectral bands into a pair-wise descriptor code that is based on a probability distribution of quantized characteristics of the adjacent spectral bands;
encoding the vector quantized indices; and
forming a bitstream of the encoded codebook indices and encoded vector quantized indices to represent the quantized transform spectrum.
2. The method of claim 1 , wherein the DCT-type transform layer is a Modified Discrete Cosine Transform (MDCT) layer and the transform spectrum is an MDCT spectrum.
3. The method of claim 1 , further comprising:
dropping a set of spectral bands to reduce the number of spectral bands prior to encoding.
4. The method of claim 1 , wherein encoding the at least two adjacent spectral bands includes
scanning adjacent pairs of spectral bands to ascertain their characteristics;
identifying a codebook index for each of the spectral bands;
obtaining a descriptor component and an extension code component for each codebook index.
5. The method of claim 4 , further comprising:
encoding a first descriptor component and a second descriptor component in pairs to obtain the pair-wise descriptor code.
6. The method of claim 4 , wherein the pair-wise descriptor code maps to one of a plurality of possible variable length codes (VLC) for different codebooks.
7. The method of claim 6 , wherein VLC codebooks are assigned to each pair of descriptor components based on a relative position of each corresponding spectral band within an audio frame and an encoder layer number.
8. The method of claim 7 , wherein the pair-wise descriptor codes are based on a quantized set of typical probability distributions of descriptor values in each pair of descriptors.
9. The method of claim 4 , wherein a single descriptor component is utilized for codebook indices greater than a value k, and extension code components are utilized for codebook indices greater than the value k.
10. The method of claim 4 , wherein each codebook index is associated a descriptor component that is based on a statistical analysis of distributions of possible codebook indices, with codebook indices having a greater probability of being selected being assigned individual descriptor components and codebook indices having a smaller probability of being selected being grouped and assigned to a single descriptor.
11. A scalable speech and audio encoder device, comprising:
a Discrete Cosine Transform (DCT)-type transform layer module adapted to
obtain a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal, wherein the Discrete Cosine Transform (DCT)-type transform layer module is further adapted to transform the residual signal at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum;
a band selector for dividing the transform spectrum into a plurality of spectral bands, each spectral band having a plurality of spectral lines;
a codebook selector for selecting a plurality of different codebooks for encoding the spectral bands, where the codebooks have associated codebook indices;
a vector quantizer for performing vector quantization on spectral lines in each spectral band using the selected codebooks to obtain vector quantized indices;
a codebook indices encoder for encoding a plurality of codebooks indices together, wherein the codebooks indices encoder includes is adapted to encode codebook indices for at least two adjacent spectral bands into a pair-wise descriptor code that is based on a probability distribution of quantized characteristics of the adjacent spectral bands;
a vector quantized indices encoder for encoding the vector; and
a transmitter for transmitting a bitstream of the encoded codebook indices and encoded vector quantized indices to represent the quantized transform spectrum.
12. The device of claim 11 , wherein the DCT-type transform layer module is a Modified Discrete Cosine Transform (MDCT) layer module and the transform spectrum is an MDCT spectrum.
13. The device of claim 11 , wherein the codebook selector is adapted to scan adjacent pairs of spectral bands to ascertain their characteristics, and further comprising:
a codebook index identifier for identifying a codebook index for each of the spectral bands; and
a descriptor selector module for obtaining a descriptor component and an extension code component for each codebook index.
14. The device of claim 11 , wherein the pair-wise descriptor code maps to one of a plurality of possible variable length codes (VLC) for different codebooks.
15. The device of claim 14 , wherein VLC codebooks are assigned to each pair of descriptor components based on a relative position of each corresponding spectral band within an audio frame and an encoder layer number.
16. A scalable speech and audio encoder device, comprising:
means for obtaining a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal;
means for transforming the residual signal at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum;
means for dividing the transform spectrum into a plurality of spectral bands, each spectral band having a plurality of spectral lines;
means for selecting a plurality of different codebooks for encoding the spectral bands, where the codebooks have associated codebook indices;
means for performing vector quantization on spectral lines in each spectral band using the selected codebooks to obtain vector quantized indices;
means for encoding the codebook indices, wherein encoding the codebooks indices includes encoding at least two adjacent spectral bands into a pair-wise descriptor code that is based on a probability distribution of quantized characteristics of the adjacent spectral bands;
means for encoding the vector quantized indices; and
means for forming a bitstream of the encoded codebook indices and encoded vector quantized indices to represent the quantized transform spectrum.
17. A non-transitory machine-readable medium comprising instructions operational for scalable speech and audio encoding, which when executed by one or more processors causes the processors to:
obtain a residual signal from a Code Excited Linear Prediction (CELP)-based encoding layer, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal;
transform the residual signal at a Discrete Cosine Transform (DCT)-type transform layer to obtain a corresponding transform spectrum;
divide the transform spectrum into a plurality of spectral bands, each spectral band having a plurality of spectral lines;
select a plurality of different codebooks for encoding the spectral bands, where the codebooks have associated codebook indices;
perform vector quantization on spectral lines in each spectral band using the selected codebooks to obtain vector quantized indices;
encode the codebook indices, wherein encoding the codebooks indices includes encoding at least two adjacent spectral bands into a pair-wise descriptor code that is based on a probability distribution of quantized characteristics of the adjacent spectral bands;
encode the vector quantized indices; and
form a bitstream of the encoded codebook indices and encoded vector quantized indices to represent the quantized transform spectrum.
18. A method for decoding in a scalable speech and audio codec, comprising:
obtaining a bitstream having a plurality of encoded codebook indices and a plurality of encoded vector quantized indices that represent a quantized transform spectrum of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer, wherein the plurality of encoded codebook indices are represented by a pair-wise descriptor code representing a plurality of adjacent transform spectrum spectral bands of an audio frame;
decoding the plurality of encoded codebook indices to obtain decoded codebook indices for a plurality of spectral bands;
decoding the plurality of encoded vector quantized indices to obtain decoded vector quantized indices for the plurality of spectral bands; and
synthesizing the plurality of spectral bands using the decoded codebook indices and decoded vector quantized indices to obtain a reconstructed version of the residual signal at an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer.
19. The method of claim 18 , wherein the IDCT-type transform layer is an Inverse Modified Discrete Cosine Transform (IMDCT) layer and the transform spectrum is an IMDCT spectrum.
20. The method of claim 18 , wherein decoding the plurality of encoded codebook indices includes
obtaining a descriptor component corresponding to each of the plurality of spectral bands;
obtaining an extension code component corresponding to each of the plurality of spectral bands;
obtaining a codebook index component corresponding to each of the plurality of spectral bands based on the descriptor component and extension code component; and
utilizing the codebook index to synthesize a spectral band for each corresponding to each of the plurality of spectral bands.
21. The method of claim 20 wherein the descriptor component is associated with a codebook index that is based on a statistical analysis of distributions of possible codebook indices, with codebook indices having a greater probability of being selected being assigned individual descriptor components and codebook indices having a smaller probability of being selected being grouped and assigned to a single descriptor.
22. The method of claim 21 , wherein a single descriptor component is utilized for codebook indices greater than a value k, and extension code components are utilized for codebook indices greater than the value k.
23. The method of claim 18 , wherein the pair-wise descriptor code is based on a probability distribution of quantized characteristics of the adjacent spectral bands.
24. The method of claim 18 , wherein the pair-wise descriptor code maps to one of a plurality of possible variable length codes (VLC) for different codebooks.
25. The method of claim 24 , wherein VLC codebooks are assigned to each pair of descriptor components is based on a relative position of each corresponding spectral band within the audio frame and an encoder layer number.
26. The method of claim 18 , wherein pair-wise descriptor codes are based on a quantized set of typical probability distributions of descriptor values in each pair of descriptors.
27. A scalable speech and audio decoder device, comprising:
a receiver to obtain a bitstream having a plurality of encoded codebook indices and a plurality of encoded vector quantized indices that represent a quantized transform spectrum of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer, wherein the plurality of encoded codebook indices are represented by a pair-wise descriptor code representing a plurality of adjacent transform spectrum spectral bands of an audio frame;
a codebook index decoder for decoding the plurality of encoded codebook indices to obtain decoded codebook indices for a plurality of spectral bands;
a vector quantized index decoder for decoding the plurality of encoded vector quantized indices to obtain decoded vector quantized indices for the plurality of spectral bands; and
a band synthesizer for synthesizing the plurality of spectral bands using the decoded codebook indices and decoded vector quantized indices to obtain a reconstructed version of the residual signal at an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer.
28. The device of claim 27 , wherein the IDCT-type transform layer module is an Inverse Modified Discrete Cosine Transform (IMDCT) layer module and the transform spectrum is an IMDCT spectrum.
29. The device of claim 27 , further comprising:
a descriptor identifier module for obtaining a descriptor component corresponding to each of the plurality of spectral bands;
an extension code identifier for obtaining an extension code component corresponding to each of the plurality of spectral bands;
a codebook index identifier for obtaining a codebook index component corresponding to each of the plurality of spectral bands based on the descriptor component and extension code component; and
a codebook selector that utilizes the codebook index and a corresponding vector quantized index to synthesize a spectral band for each corresponding to each of the plurality of spectral bands.
30. The device of claim 27 , wherein the pair-wise descriptor code is based on a probability distribution of quantized characteristics of the adjacent spectral bands.
31. The device of claim 27 , wherein pair-wise descriptor codes are based on a quantized set of typical probability distributions of descriptor values in each pair of descriptors.
32. A scalable speech and audio decoder device, comprising:
means for obtaining a bitstream having a plurality of encoded codebook indices and a plurality of encoded vector quantized indices that represent a quantized transform spectrum of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer, wherein the plurality of encoded codebook indices are represented by a pair-wise descriptor code representing a plurality of adjacent transform spectrum spectral bands of an audio frame;
means for decoding the plurality of encoded codebook indices to obtain decoded codebook indices for a plurality of spectral bands;
means for decoding the plurality of encoded vector quantized indices to obtain decoded vector quantized indices for the plurality of spectral bands; and
means for synthesizing the plurality of spectral bands using the decoded codebook indices and decoded vector quantized indices to obtain a reconstructed version of the residual signal at an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer.
33. A non-transitory machine-readable medium comprising instructions operational for scalable speech and audio decoding, which when executed by one or more processors causes the processors to:
obtain a bitstream having a plurality of encoded codebook indices and a plurality of encoded vector quantized indices that represent a quantized transform spectrum of a residual signal, where the residual signal is a difference between an original audio signal and a reconstructed version of the original audio signal from a Code Excited Linear Prediction (CELP)-based encoding layer, wherein the plurality of encoded codebook indices are represented by a pair-wise descriptor code representing a plurality of adjacent transform spectrum spectral bands of an audio frame;
decode the plurality of encoded codebook indices to obtain decoded codebook indices for a plurality of spectral bands;
decode the plurality of encoded vector quantized indices to obtain decoded vector quantized indices for the plurality of spectral bands; and
synthesize the plurality of spectral bands using the decoded codebook indices and decoded vector quantized indices to obtain a reconstructed version of the residual signal at an Inverse Discrete Cosine Transform (IDCT)-type inverse transform layer.