Method and system for reduction of quantization-induced block-discontinuities and general purpose audio codec

1. A computer-implemented method for ultra-low latency decompression for a general-purpose audio input signal, including:

decoding, by a processor, an input bit stream into quantization indices and residue quantization indices;

applying an inverse quantization algorithm to the quantization indices to generate signal coefficients;

applying an inverse transform to the signal coefficients to generate a time-domain reconstructed signal waveform;

applying a stochastic noise synthesis algorithm to the residue quantization indices to generate a time-domain reconstructed residue waveform;

combining, by the processor, the reconstructed signal waveform and the reconstructed residue waveform as a reconstructed signal waveform block; and

generating an output signal by applying a boundary synthesis algorithm to the reconstructed signal waveform blocks.

2. The method of claim 1 , wherein applying the stochastic noise synthesis algorithm comprises:

generating pseudo-random numbers;

scaling the pseudo-random numbers by residue energy to produce synthesized discrete cosine transform (DCT) or fast Fourier transform (FFT) coefficients; and

performing an inverse-DCT or inverse-FFT to obtain a time-domain synthesized noise subframe signal.

3. The method of claim 1 , wherein applying the stochastic noise synthesis algorithm comprises:

pre-computing band-limited filter coefficients for a plurality of frequency bands;

generating a pseudo-random white noise;

applying the band-limited filter coefficients to the pseudo-random white noise to produce a spectrally colored stochastic noise for each frequency band;

computing a noise gain curve for each frequency band by interpolating encoded residue energy levels among residue sub-frames and between audio coding frames;

applying each gain curve to a spectrally colored noise signal; and

adding the spectrally colored noise signal to a corresponding frequency band to produce the time-domain reconstructed residue waveform.

4. The method of claim 1 , wherein applying the stochastic noise synthesis algorithm comprises:

calculating subband sizes from a best basis tree;

splitting each subband or joining neighboring subbands to create noise subframes that are within a specified range of subframe sizes; and

placing the ordered noise subframe signal into a reconstructed noise frame utilizing the subframe sizes.

5. The method of claim 1 , wherein applying the inverse transform to the signal coefficients further comprises:

pre-calculating bell window functions;

joining an extended best basis tree into a combined best basis tree; and

performing a cosine packet synthesis to recover the time-domain reconstructed signal waveform based on the bell window functions and the combined best basis tree.

6. The method of claim 5 , wherein the extended best basis tree is a two-dimensional data array, and the combined best basis tree is a one-dimensional data array.

7. The method of claim 1 , further comprising:

renormalizing the reconstructed signal waveform block to generate a renormalization block by multiplying a normalization factor with the reconstructed signal waveform block.

8. The method of claim 7 , further comprising:

buffering a synthesis history, wherein the synthesis history comprises a plurality of samples from a last coding frame.

9. The method of claim 8 , further comprising:

combining the samples of the synthesis history and a portion of samples of the normalization block to generate a synthesized waveform block;

updating the synthesis history by buffering a plurality of samples of a current coding frame; and

clipping the synthesized waveform block to generate the output signal.

10. The method of claim 9 , wherein combining the samples of the synthesis history and the portion of samples of the normalization block further comprises:

generating a linear interpolation based on the samples of the synthesis history and the portion of samples of the normalization block.

11. A computer program, residing on a non-transitory computer-readable medium, for ultra-low latency decompression for a general-purpose audio input signal, the computer program comprising instructions for causing a processor to:

decode an input bit stream into quantization indices and residue quantization indices;

apply an inverse quantization algorithm to the quantization indices to generate signal coefficients;

apply an inverse transform to the signal coefficients to generate a time-domain reconstructed signal waveform;

apply a stochastic noise synthesis algorithm to the residue quantization indices to generate a time-domain reconstructed residue waveform;

combine the reconstructed signal waveform and the reconstructed residue waveform as a reconstructed signal waveform block; and

generate an output signal by applying a boundary synthesis algorithm to the reconstructed signal waveform blocks.

12. The computer program of claim 11 , wherein the instructions for causing the processor to apply a stochastic noise synthesis algorithm includes instructions for causing the processor to:

generate pseudo-random numbers;

scale the pseudo-random numbers by residue energy to produce synthesized DCT or FFT coefficients; and

perform an inverse-DCT or inverse-FFT to obtain a time-domain synthesized noise subframe signal.

13. The computer program of claim 11 , wherein the instructions for causing the processor to apply a stochastic noise synthesis algorithm includes instructions for causing the processor to:

pre-compute band-limited filter coefficients for a plurality of frequency bands;

generate a pseudo-random white noise;

apply the band-limited filter coefficients to the pseudo-random white noise to produce spectrally colored stochastic noise for each frequency band;

compute a noise gain curve for each frequency band by interpolating encoded residue energy levels among residue sub-frames and between audio coding frames;

apply each gain curve to a spectrally colored noise signal; and

add the spectrally colored noise signal to a corresponding frequency band to produce a final synthesized noise signal.

14. The computer program of claim 11 , wherein the instructions for causing the processor to apply the stochastic noise synthesis algorithm includes instructions for causing the processor to:

calculate subband sizes from a best basis tree;

split each subband or joining neighboring subbands to create noise subframes that are within a specified range of subframe sizes; and

place the ordered noise subframe signal into a reconstructed noise frame utilizing the subframe sizes.

15. The computer program of claim 11 , wherein the computer program further comprises instructions for causing the processor to:

pre-calculate bell window functions;

join an extended best basis tree into a combined best basis tree; and

perform a cosine packet synthesis to recover the time-domain reconstructed signal waveform based on the bell window functions and the combined best basis tree.

16. The computer program of claim 15 , wherein the extended best basis tree is a two-dimensional data array, and the combined best basis tree is a one-dimensional data array.

17. The computer program of claim 11 , wherein the computer program further comprises instructions for causing the processor to:

renormalize the reconstructed signal waveform block to generate a renormalization block by multiplying a normalization factor with the reconstructed signal waveform block.

18. The computer program of claim 17 , wherein the computer program further comprises instructions for causing the processor to:

buffer a synthesis history, wherein the synthesis history comprises a plurality of samples from a last coding frame.

19. The computer program of claim 18 , wherein the computer program further comprises instructions for causing the processor to:

combine the samples of the synthesis history and a portion of samples of the normalization block to generate a synthesized waveform block;

update the synthesis history by buffering a plurality of samples of a current coding frame; and

clip the synthesized waveform block to generate the output signal.

20. The computer program of claim 19 , wherein the computer program further comprises instructions for causing the processor to:

generate a linear interpolation based on the samples of the synthesis history and the portion of samples of the normalization block.