Methods and apparatus for efficient quantization of gain parameters in GLPAS speech coders

• US 6,240,385 B1
• Filed: 09/24/1998
• Issued: 05/29/2001
• Est. Priority Date: 05/29/1998
• Status: Expired due to Term

• Current Assignee: Blackberry Limited
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Foodeei, Majid
• Primary Examiner(s): Dorvil, Richemond
• Application Number:
  US09/161,429
• Time in Patent Office: 978 Days
• Field of Search: 704/220, 704/225, 704/230, 704/222, 704/219, 704/502, 704/500, 704/262, 704/266, 704/268
• US Class Current: 704/220
• CPC Class Codes: G10L 19/083 the excitation function being an excitation gain G10L25/90 takes precedence

Abstract

In methods and apparatus for encoding a gain parameter in a generalized linear predictive analysis-by-synthesis (GLPAS) coder, a subframe gain parameter is determined for each of a plurality of successive subframes of a frame, and a quantized frame gain parameter is determined for each frame using a delayed decision quantizer operating on the subframe gain parameters. The subframe gain parameters may be treated as components of a gain vector and the gain vector may be vector quantized to determine the quantized frame gain parameter. Encoder parameters are efficiently aligned with decoder parameters to ensure proper end-to-end operation. Alternatively, tree quantization or trellis quantization may be applied to the subframe gain parameters to determine the quantized frame gain parameter. The methods and apparatus are particularly applicable to low bit rate speech coding.

Claims

1. A method of encoding a gain parameter in a generalized linear predictive analysis-by-synthesis coder, comprising:

determining a quantized frame gain parameter for each of a plurality of successive subframes of a frame of an encoded audio signal; and

determining a quantized frame gain parameter for each frame of the encoded audio signal using a delayed decision quantizer operating on the subframe gain parameters.

2. A method as defined in claim 1, wherein the step of determining a quantized frame gain parameter comprises treating the subframe gain parameters as components of a gain vector and vector quantizing the gain vector to determine the quantized frame gain parameter.

3. A method as defined in claim 2, wherein the step of vector quantizing the gain vector comprises quantizing the gain vector by analysis-by-synthesis linear predictive vector quantization.

4. A method as defined in claim 3, wherein the step of vector quantizing the gain vector by analysis-by-synthesis linear predictive vector quantization comprises adaptation of a synthesis filter.

5. A method as defined in claim 3, wherein the step of vector quantizing the gain vector comprises application of auto-regressive predictive vector quantization.

6. A method as defined in claim 3, wherein the step of vector quantizing the gain vector comprises application of moving average predictive vector quantization.

7. A method as defined in claim 2, wherein the step of quantizing the gain vector comprises quantizing the gain vector by adaptive analysis-by-synthesis linear vector quantization.

8. A method as defined in claim 2, comprising determining multiple subframe gain parameters for each subframe, treating the subframe gain parameters as components of a gain vector and vector quantizing the gain vector to determine the quantized frame gain parameter.

9. A method as defined in claim 2, comprising determining a fixed codebook gain and an adaptive codebook gain for each subframe, treating the fixed codebook gains and adaptive codebook gains as components of a gain vector and a vector quantizing the gain vector to determine the quantized gain parameter.

10. A method as defined in claim 2, comprising determining a fixed codebook gain and a pitch gain for each subframe, treating the fixed codebook gains and long term predictor gains as components of a gain vector and vector quantizing the gain vector to determine the quantized gain parameter.

11. A method as defined in claim 2, wherein the step of vector quantizing the gain vector comprises applying a linear transform to the gain vector to generate a transformed gain vector and vector quantizing a selected portion of the transformed gain vector.

12. A method as defined in claim 11, wherein the step of applying a linear transform to the gain vector comprises applying a discrete cosine transform to the gain vector.

13. A method as defined in claim 2, wherein the step of vector quantizing the gain vector comprises calculating a mean value of the gain vector, scalar quantizing the mean value, subtracting the quantized mean value from the gain vector to generate a mean-removed gain vector and vector quantizing the mean-removed gain vector.

14. A method as defined in claim 13, wherein the step of scalar quantizing the mean value of the gain vector comprises predictive scalar quantizing the mean value of the gain vector.

15. A method as defined in claim 2, wherein the step of vector quantizing the gain vector comprises vector quantizing the gain vector to generate a first stage vector quantization index, subtracting a vector corresponding to the first stage vector quantization index from the gain vector to generate a residual gain vector and vector quantizing the residual gain vector to generate a second stage vector quantization index.

16. A method as defined in claim 2, wherein the step of vector quantizing the gain parameter comprises encoding the gain parameter as a gain codebook index corresponding to a gain codebook vector, said gain codebook vector providing a synthesized speech signal having a minimum difference from a speech signal to be encoded.

17. A method as defined in claim 1, wherein the step of determining a quantized frame gain parameter comprises applying tree quantization to the subframe gain parameters.

18. A method as defined in claim 1, wherein the step of determining a quantized frame gain parameter comprises applying trellis quantization to the subframe gain parameters.

19. A method as defined in claim 1, further comprising updating parameters of the coder using the quantized frame gain parameter.

20. A generalized linear predictive analysis-by-synthesis coder for encoding an audio signal, comprising means for encoding a gain parameter, said means comprising:

means for determining a subframe gain parameter for each of a plurality of successive subframes of a frame of an encoded audio signal; and

delayed decision quantization means operable on the subframe gain parameters for determining a quantized frame gain parameter for each frame of the encoded audio signal.

21. A coder as defined in claim 20, wherein the delayed decision quantization means comprises a vector quantizer which treats the subframe gain parameters as components of a gain vector, vector quantizing the gain vector to determine the quantized frame gain parameter.

22. A coder as defined in claim 21, wherein the delayed decision quantization means comprises a quantizer selected from the class consisting of tree quantizers and trellis quantizers.

23. A transmission system, comprising:

a linear predictive analysis-by-synthesis coder comprising means for encoding a gain parameter, said means comprising means for determining a subframe gain parameter for each of a plurality of successive subframes of a frame of an encoded audio signal, and delayed decision quantization means operable on the subframe gain parameters for determining a quantized frame gain parameter for each frame of the digitally encoded audio signal;

a decoder comprising means for determining a quantized gain vector for the current frame of the encoded audio signal from a received gain vector codebook index, and means for applying respective components of the quantized gain vector to successive subframes of a signal synthesized at the decoder; and

a transmission medium linking the coder to the decoder.

24. A method of decoding an encoded audio signal having a vector quantized gain parameter, components of a quantized gain vector for a frame of the encoded audio signal corresponding to gain parameters for each successive subframe of the frame, comprising:

determining a quantized gain vector for the current frame of the encoded audio signal from a received gain vector codebook index; and

applying respective components of the quantized gain vector to successive subframes of an audio signal synthesized at the decoder.

25. A decoder for decoding an encoded audio signal having a vector quantized gain parameter, components of a quantized gain vector for a frame corresponding to gain parameters for successive subframes of the frame, the decoder comprising;

means for determining a quantized gain vector for the current frame of the encoded audio signal from a received gain vector codebook index; and

means for applying respective components of the quantized gain vector to successive subframes of an audio signal synthesized at the decoder.