Spectral noise shaping in audio coding based on spectral dynamics in frequency sub-bands

1. A method of spectral noise shaping in an audio coding apparatus, comprising:

determining whether an audio signal is tonal;

time domain linear prediction (TDLP) processing the tonal audio signal with the audio coding apparatus to produce a residual signal and linear predictive coding (LPC) coefficients; and

applying a frequency domain linear prediction (FDLP) process to the residual signal with the audio coding apparatus.

2. The method of claim 1 , further comprising:

encoding FDLP parameters from the FDLP process and the LPC coefficients; and

transmitting the encoded FDLP parameters LPC coefficients to a decoder.

3. The method of claim 2 , further comprising:

at the decoder:

decoding the encoded FDLP parameters and LPC coefficients to yield decoded FDLP parameters and decoded LPC coefficients;

applying an inverse FDLP process to the decoded FDLP parameters to yield a reconstructed residual signal; and

applying inverse TDLP process to the reconstructed residual signal and the decoded LPC coefficients to yield a reconstructed audio signal.

4. The method of claim 1 , further comprising:

generating a tonality flag indicating that the audio signal is tonal; and

transmitting the tonality flag to a decoder.

5. The method of claim 1 , wherein determining includes:

determining a global tonality measure;

determining a local tonality measure; and

determining whether the audio signal is tonal based on the global and local tonality measures.

6. The method of claim 5 , wherein the global tonality measure is based on a spectral flatness measure (SFM) computed over a predetermined frame of a full-band audio signal corresponding to the audio signal.

7. The method of claim 6 , further comprising:

comparing the SFM to a predetermined threshold; and

declaring the audio signal to be non-tonal if the SFM is above the predetermined threshold.

8. The method of claim 7 , further comprising:

computing the local tonality measure of a frequency sub-band corresponding to the audio signal, if the SFM is below the predetermined threshold.

9. The method of claim 5 , wherein determining the local tonality measure includes:

computing a discrete cosine transform (DCT) of the audio signal;

computing a plurality of auto-correlation values from the DCT;

determining a maximum auto-correlation value; and

computing the ratio of the maximum auto-correlation value to the energy of the DCT, wherein the local tonality measure is based on the ratio.

10. The method of claim 5 , further comprising:

providing a predetermined global tonality threshold and a predetermined local tonality threshold, each for comparison with the global tonality measure and local tonality measure, respectively.

11. The method of claim 10 , wherein the predetermined global tonality threshold and the predetermined local tonality threshold are each determined empirically.

12. An apparatus, comprising:

means for determining whether an audio signal is tonal to provide a tonal audio signal;

means for time domain linear prediction (TDLP) processing the tonal audio signal to produce a residual signal and linear predictive coding (LPC) coefficients; and

means for applying a frequency domain linear prediction (FDLP) process to the residual signal.

13. The apparatus of claim 12 , further comprising:

means for encoding FDLP parameters from the FDLP process and the LPC coefficients; and

means for transmitting the encoded FDLP parameters LPC coefficients to a decoder.

14. The apparatus of claim 13 , further comprising:

at the decoder:

means for decoding the encoded FDLP parameters and LPC coefficients to yield decoded FDLP parameters and decoded LPC coefficients;

means for applying an inverse FDLP process to the decoded FDLP parameters to yield a reconstructed residual signal; and

means for applying inverse TDLP process to the reconstructed residual signal and the decoded LPC coefficients to yield a reconstructed audio signal.

15. The apparatus of claim 12 , further comprising:

means for generating a tonality flag indicating that the audio signal is tonal; and

means for transmitting the tonality flag to a decoder.

16. The apparatus of claim 12 , wherein the determining means includes:

means for determining a global tonality measure;

means for determining a local tonality measure; and

means for determining whether the audio signal is tonal based on the global and local tonality measures.

17. The apparatus of claim 16 , wherein the global tonality measure is based on a spectral flatness measure (SFM) computed over a predetermined frame of a full-band audio signal corresponding to the audio signal.

18. The apparatus of claim 17 , further comprising:

means for comparing the SFM to a predetermined threshold; and

means for declaring the audio signal to be non-tonal if the SFM is above the predetermined threshold.

19. The apparatus of claim 18 , further comprising:

means for computing the local tonality measure of a frequency sub-band corresponding to the audio signal, if the SFM is below the predetermined threshold.

20. The apparatus of claim 16 , wherein means for determining the local tonality measure includes:

means for computing a discrete cosine transform (DCT) of the audio signal;

means for computing a plurality of auto-correlation values from the DCT;

means for determining a maximum auto-correlation value; and

means for computing the ratio of the maximum auto-correlation value to the energy of the DCT, wherein the local tonality measure is based on the ratio.

21. The apparatus of claim 16 , further comprising:

means for providing a predetermined global tonality threshold and a predetermined local tonality threshold, each for comparison with the global tonality measure and local tonality measure, respectively.

22. The apparatus of claim 21 , wherein the predetermined global tonality threshold and the predetermined local tonality threshold are each determined empirically.

23. The apparatus of claim 12 , included in a wireless communication device.

24. An apparatus, comprising:

a tonality detector configured to output a tonal audio signal based on a determination of whether an audio signal is tonal;

a time domain linear prediction (TDLP) process configured to produce a residual signal and linear predictive coding (LPC) coefficients in response to the tonal audio signal; and

a frequency domain linear prediction (FDLP) component configured to process the residual signal;

wherein the TDLP process or the FDLP component are implemented, at least in part, in hardware.

25. The apparatus of claim 24 , further comprising:

an encoder configured to encode FDLP parameters from the FDLP component and the LPC coefficients; and

a transmitter configured to transmit the encoded FDLP parameters LPC coefficients to a decoder.

26. The apparatus of claim 25 , further comprising:

the decoder configured to decode the encoded FDLP parameters and LPC coefficients to yield decoded FDLP parameters and decoded LPC coefficients;

an inverse FDLP component configured to process the decoded FDLP parameters to yield a reconstructed residual signal; and

an inverse TDLP process configured to produce a reconstructed audio signal in response to the reconstructed residual signal and the decoded LPC coefficients.

27. The apparatus of claim 24 , wherein the tonality detector is further configured to generate a tonality flag indicating that the audio signal is tonal; and the apparatus further comprises a transmitter configured to transmit the tonality flag to a decoder.

28. The apparatus of claim 24 , wherein the tonality detector includes:

a global tonality calculator configured to determine global tonality measure;

a local tonality calculator configured to determine a local tonality measure; and

a comparator configured to determine whether the audio signal is tonal based on the global and local tonality measures.

29. The apparatus of claim 28 , wherein the global tonality measure is based on a spectral flatness measure (SFM) computed over a predetermined frame of a full-band audio signal corresponding to the audio signal.

30. The apparatus of claim 29 , wherein the comparator is configured to compare the SFM to a predetermined threshold and to declare the audio signal to be non-tonal if the SFM is above the predetermined threshold.

31. The apparatus of claim 30 , wherein the local tonality calculator is further configured to compute the local tonality measure of a frequency sub-band corresponding to the audio signal, if the SFM is below the predetermined threshold.

32. The apparatus of claim 28 , wherein the local tonality calculator includes:

a DCT calculator configured to computer a discrete cosine transform (DCT) of the audio signal;

an auto-correlator configured to compute a plurality of auto-correlation values from the DCT;

a maximum value detector configured to determine a maximum auto-correlation value; and

a ratio calculator configured to compute the ratio of the maximum auto-correlation value to the energy of the DCT, wherein the local tonality measure is based on the ratio.

33. The apparatus of claim 28 , further comprising:

a threshold calculator configured to provide a predetermined global tonality threshold and a predetermined local tonality threshold, each for comparison with the global tonality measure and local tonality measure, respectively.

34. The apparatus of claim 33 , wherein the predetermined global tonality threshold and the predetermined local tonality threshold are each determined empirically.

35. The apparatus of claim 24 , included in a wireless communication device.

36. A non-transitory computer-readable medium embodying a set of instructions executable by one or more processors, comprising:

code for determining whether an audio signal is tonal to provide a tonal audio signal;

code for time domain linear prediction (TDLP) processing the tonal audio signal to produce a residual signal and linear predictive coding (LPC) coefficients; and

code for applying a frequency domain linear prediction (FDLP) process to the residual signal.

37. The computer-readable medium of claim 36 , further comprising:

code for encoding FDLP parameters from the FDLP process and the LPC coefficients; and

code for transmitting the encoded FDLP parameters LPC coefficients to a decoder.

38. The computer-readable medium of claim 37 , further comprising:

code for decoding the encoded FDLP parameters and LPC coefficients to yield decoded FDLP parameters and decoded LPC coefficients;

code for applying an inverse FDLP process to the decoded FDLP parameters to yield a reconstructed residual signal; and

code for applying inverse TDLP process to the reconstructed residual signal and the decoded LPC coefficients to yield a reconstructed audio signal.

39. The computer-readable medium of claim 36 , further comprising:

code for generating a tonality flag indicating that the audio signal is tonal; and

code for transmitting the tonality flag to a decoder.

40. The computer-readable medium of claim 36 , wherein the determining code includes:

code for determining a global tonality measure;

code for determining a local tonality measure; and

code for determining whether the audio signal is tonal based on the global and local tonality measures.

41. The computer-readable medium of claim 40 , wherein the global tonality measure is based on a spectral flatness measure (SFM) computed over a predetermined frame of a full-band audio signal corresponding to the audio signal.

42. The computer-readable medium of claim 41 , further comprising:

code for comparing the SFM to a predetermined threshold; and

code for declaring the audio signal to be non-tonal if the SFM is above the predetermined threshold.

43. The computer-readable medium of claim 42 , further comprising:

code for computing the local tonality measure of a frequency sub-band corresponding to the audio signal, if the SFM is below the predetermined threshold.

44. The computer-readable medium of claim 40 , wherein code for determining the local tonality measure includes:

code for computing a discrete cosine transform (DCT) of the audio signal;

code for computing a plurality of auto-correlation values from the DCT;

code for determining a maximum auto-correlation value; and

code for computing the ratio of the maximum auto-correlation value to the energy of the DCT, wherein the local tonality measure is based on the ratio.

45. The computer-readable medium of claim 40 , further comprising:

code for providing a predetermined global tonality threshold and a predetermined local tonality threshold, each for comparison with the global tonality measure and local tonality measure, respectively.

46. The computer-readable medium of claim 45 , wherein the predetermined global tonality threshold and the predetermined local tonality threshold are each determined empirically.