Method and apparatus for applying linear prediction to critical band subbands of split-band perceptual coding systems

• US 5,699,484 A
• Filed: 04/26/1996
• Issued: 12/16/1997
• Est. Priority Date: 12/20/1994
• Status: Expired due to Term

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Davis, Mark Franklin
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): EDOUARD, PATRICK NESTOR
• Application Number:
  US08/638,498
• Time in Patent Office: 599 Days
• Field of Search: 395/2.28, 395/2.38, 395/2.39, 395/2.14, 395/2.2, 395/2.21, 395/2.29, 381/29-41
• US Class Current: 704/200.1
• CPC Class Codes: G10L 25/12 the extracted parameters being prediction coefficients
• CPC Class Codes: H04B 1/665 using psychoacoustic properties of the ear, e.g. masking effect

Abstract

A split-band perceptual coding system utilizes generalized waveform predictive coding in frequency bands to further reduce coded signal information requirements. The system including frequency subband each having a bandwidth commensurate with or less than a corresponding critical band of human perception. The order of the predictors are selected to balance requirements for prediction accuracy and rapid response time. Predictive coding may be adaptively inhibited in a band during intervals in which no predictive coding gain is realized.

Claims

1. An encoding method comprising the steps of:

receiving an input signal representing audio information,

generating a plurality of subband signals, each subband signal corresponding to a respective frequency subband of said input signal having a bandwidth commensurate with or less than a corresponding critical band of human perception,

generating subband information by predicting a respective subband signal using a waveform predictor having an order greater than or equal to a minimum order, said minimum order equal to three, and

formatting an encoded signal by assembling said subband information into a form suitable for transmission or storage.

2. An encoding method according to claim 1 wherein said waveform predictor is implemented by a digital filter having filter coefficients adapted in response to a recovered replica of said respective subband signal.

3. An encoding method according to claim 1 wherein said respective subband signal comprises samples having a time interval between adjacent samples, and wherein said waveform predictor has an order of not more than a maximum order substantially equal to the postmasking interval of the human auditory system divided by said time interval.

7. An encoding method according to claim 3 or 6 wherein said subband signals are generated by applying a discrete transform to said input signal, and wherein said minimum order is equal to 4, 6 and 8 for discrete transform lengths of 512, 256 and 128, respectively.

8. An encoding method according to claim 7 wherein said discrete transform substantially corresponds to either an evenly-stacked Time Domain Aliasing Cancellation transform or an oddly-stacked Time Domain Aliasing Cancellation transform.

9. An encoding method according to claim 2 or 5 wherein said filter coefficients are adapted at a rate varying inversely with amplitude of said respective subband signal.

11. An encoding method according to claim 1 or 4 wherein said input signal comprises input signal samples and each of said subband signals comprise one or more transform coefficients, said transform coefficients generated by applying a transform to said input signal.

12. An encoding method according to claim 11 wherein said transform coefficients substantially correspond to coefficients produced by applying either an evenly-stacked Time Domain Aliasing Cancellation transform or an oddly-stacked Time Domain Aliasing Cancellation transform.

4. An encoding method comprising the steps of:

receiving an input signal representing audio information,

generating a plurality of subband signals, each subband signal corresponding to a respective frequency subband of said input signal having a bandwidth commensurate with or less than a corresponding critical band of human perception,

generating quantized information by processing a respective subband signal, said processing comprising the steps of;

generating a predicted signal by applying a predictor to said respective subband signal, said predictor having an order greater than or equal to a minimum order, said minimum order equal to three,

generating a prediction error signal from the difference between said respective subband signal and said predicted signal, and

generating said quantized information by quantizing said prediction error signal, and

formatting an encoded signal by assembling said quantized information into a form suitable for transmission or storage.

5. An encoding method according to claim 4 wherein said predictor is implemented by a digital filter having filter coefficients adapted in response to a recovered replica of said respective subband signal.

6. An encoding method according to claim 4 wherein said respective subband signal comprises samples having a time interval between adjacent samples, and wherein said predictor has an order of not more than a maximum order substantially equal to the postmasking interval of the human auditory system divided by said time interval.

10. An encoding method according to claim 4 further comprising a step for determining information requirements of said prediction error signal and said respective subband signal, wherein said quantized information is generated by quantizing said respective subband signal rather than said prediction error signal when the information requirements of said respective subband signal is lower than said prediction error signal.

13. A decoding method comprising the steps of:

receiving an encoded signal representing audio information and obtaining therefrom subband information for respective frequency subbands of said audio information having bandwidths commensurate with or less than a corresponding critical band of human perception,

generating a respective subband signal for each of a plurality of subbands by applying a waveform predictor to subband information for a respective subband, said predictor having an order greater than or equal to a minimum order, said minimum order equal to three, and

generating a replica of said audio information in response to said respective subband signal for each of a plurality of subbands.

14. A decoding method according to claim 13 wherein, for a respective subband, said waveform predictor is implemented by a digital filter having filter coefficients adapted in response to said subband signal.

15. A decoding method according to claim 13 wherein said respective subband signal comprises samples having a time interval between adjacent samples, and wherein said waveform predictor has an order of not more than a maximum order substantially equal to the postmasking interval of the human auditory system divided by said time interval.

19. A decoding method according to claim 15 or 18 wherein said replica of said audio information is generated by applying an inverse discrete transform to subband signals in said plurality of subbands, and wherein said minimum order is equal to 4, 6 and 8 for inverse discrete transform lengths of 512, 256 and 128, respectively.

20. A decoding method according to claim 19 wherein said inverse discrete transform substantially corresponds to either an evenly-stacked Time Domain Aliasing Cancellation inverse transform or an oddly-stacked Time Domain Aliasing Cancellation inverse transform.

21. A decoding method according to claim 14 or 17 wherein said filter coefficients are adapted at a rate varying inversely with amplitude of said respective subband signal.

22. A decoding method according to claim 13 or 16 wherein said subband signal comprises transform coefficients, said replica of said audio information generated by applying an inverse transform to said subband signal for each of a plurality of subbands.

23. A decoding method according to claim 22 wherein said inverse transform substantially corresponds to either an evenly-stacked Time Domain Aliasing Cancellation inverse transform or an oddly-stacked Time Domain Aliasing Cancellation inverse transform.

16. A decoding method comprising the steps of:

receiving an encoded signal representing audio information and obtaining therefrom subband information for respective frequency subbands of said audio information having bandwidths commensurate with or less than a corresponding critical band of human perception, wherein said subband information corresponds to either prediction errors or a subband signal,

generating a respective subband signal for each subband represented by subband information corresponding to prediction errors by applying a predictor to the subband information, said predictor having an order greater than or equal to a minimum order, said minimum order equal to three, and

generating a replica of said audio information in response to said respective subband signal for each of said subbands.

17. A decoding method according to claim 16 wherein, for a respective subband, said predictor is implemented by a digital filter having filter coefficients adapted in response to said subband signal.

18. A decoding method according to claim 16 wherein said respective subband signal comprises samples having a time interval between adjacent samples, and wherein said predictor has an order of not more than a maximum order substantially equal to the postmasking interval of the human auditory system divided by said time interval.

24. An encoder comprising:

an input terminal,

a plurality of bandpass filters coupled to said input terminal, said bandpass filters having respective center frequencies and respective passband bandwidths commensurate with or narrower than critical bands of the human auditory system,

a prediction circuit coupled to a respective bandpass filter, said prediction circuit comprising a prediction filter and a quantizer, said prediction filter having an order greater than or equal to a minimum order, said minimum order equal to three, and

a multiplexor coupled to said linear prediction circuit.

25. An encoder according to claim 24 wherein a respective one of said bandpass filters is implemented by a digital filter generating digital values having a time interval between adjacent digital values, and wherein said prediction filter coupled to said respective bandpass filter has an order of not more than a maximum order substantially equal to the postmasking interval of the human auditory system divided by said time interval.

28. An encoder according to claim 25 or 27 wherein said plurality of bandpass filters is implemented by a time-domain to frequency-domain transform, and wherein said minimum order is equal to 4, 6 and 8 for transform lengths of 512, 256 and 128, respectively.

29. An encoder according to claim 28 wherein said transform substantially corresponds to either an evenly-stacked Time Domain Aliasing Cancellation transform or an oddly-stacked Time Domain Aliasing Cancellation transform.

30. An encoder according to claim 24 or 26 wherein said plurality of bandpass filters is implemented by a time-domain to frequency-domain transform.

31. An encoder according to claim 30 wherein said transform substantially corresponds to either an evenly-stacked Time Domain Aliasing Cancellation transform or an oddly-stacked Time Domain Aliasing Cancellation transform.

32. An encoder according to claim 24 or 26 wherein said prediction filter comprises a filter tap having a weighting circuit, said weighting circuit coupled to said quantizer.

26. An encoder comprising:

an input terminal,

a plurality of bandpass filters coupled to said input terminal, said bandpass filters having respective center frequencies and respective passband bandwidths commensurate with or narrower than critical bands of the human auditory system,

a prediction circuit having an input coupled to a respective bandpass filter and having an output, said prediction circuit comprising a prediction filter having an order greater than or equal to a minimum order, said minimum order equal to three,

a comparator having a first input, a second input and an output, said first input of said comparator coupled to said respective bandpass filter and said second input of said comparator coupled to said output of said prediction circuit,

a switch control coupled to said output of said comparator,

a switch with a first input, a second input and an output, said first input of said switch coupled to said respective bandpass filter and said second input of said switch coupled to said output of said prediction circuit, wherein said output of said switch is switchably connected to either said first input of said switch or said second input of said switch in response to said switch control,

a quantizer having an input coupled to said output of said switch and having an output, and

a multiplexor coupled to said output of said quantizer.

27. An encoder according to claim 26 wherein a respective one of said bandpass filters is implemented by a digital filter generating digital values having a time interval between adjacent digital values, and wherein said prediction filter coupled to said respective bandpass filter has an order of not more than a maximum order substantially equal to the postmasking interval of the human auditory system divided by said time interval.

33. A decoder comprising:

an input terminal,

a demultiplexor having an input and a plurality of outputs, said input of said demultiplexor coupled to said input terminal,

a prediction circuit coupled to a respective one of said plurality of outputs of said demultiplexor, said prediction circuit comprising a prediction filter having an order greater than or equal to a minimum order, said minimum order equal to three, and

a plurality of inverse bandpass filters having respective center frequencies and respective passband bandwidths commensurate with or narrower than critical bands of the human auditory system, a respective one of said plurality of inverse bandpass filters coupled to said prediction circuit.

34. A decoder according to claim 33 wherein a respective one of said prediction filters is implemented by a digital filter generating digital values having a time interval between adjacent digital values, said respective prediction filter having an order of not more than a maximum order substantially equal to the postmasking interval of the human auditory system divided by said time interval.

37. A decoder according to claim 34 or 36 wherein said plurality of inverse bandpass filters are implemented by a frequency-domain to time-domain transform, and wherein said minimum order is equal to 4, 6 and 8 for transform lengths of 512, 256 and 128, respectively.

38. A decoder according to claim 37 wherein said transform substantially corresponds to either an evenly-stacked Time Domain Aliasing Cancellation inverse transform or an oddly-stacked Time Domain Aliasing Cancellation inverse transform.

39. A decoder according to claim 33 or 35 wherein said plurality of inverse bandpass filters are implemented by a frequency-domain to time-domain transform.

40. A decoder according to claim 39 wherein said transform substantially corresponds to either an evenly-stacked Time Domain Aliasing Cancellation inverse transform or an oddly-stacked Time Domain Aliasing Cancellation inverse transform.

41. A decoder according to claim 33 or 35 wherein said prediction filter comprises a filter tap having a weighting circuit, said weighting circuit coupled to said respective one of said plurality of outputs of said demultiplexor.

35. A decoder comprising:

an input terminal,

a demultiplexor having an input and a plurality of demultiplexor outputs, said input of said demultiplexor coupled to said input terminal,

a prediction circuit having an input coupled to a respective one of said plurality of demultiplexor outputs and having an output, said prediction circuit comprising a prediction filter having an order greater than or equal to a minimum order, said minimum order equal to three,

a switch control coupled to said respective one of said plurality of demultiplexor outputs,

a switch with a first input, a second input and an output, said first input of said switch coupled to said respective one of said plurality of demultiplexor outputs and said second input of said switch coupled to said output of said prediction circuit, wherein said output of said switch is switchably connected to either said first input of said switch or said second input of said switch in response to said switch control, and

a plurality of inverse bandpass filters having respective center frequencies and respective passband bandwidths commensurate with or narrower than critical bands of the human auditory system, a respective one of said plurality of inverse bandpass filters coupled to said output of said switch.

36. A decoder according to claim 35 wherein a respective one of said prediction filters is implemented by a digital filter generating digital values having a time interval between adjacent digital values, said respective prediction filter having an order of not more than a maximum order substantially equal to the postmasking interval of the human auditory system divided by said time interval.