Methods and systems for bit allocation and partitioning in gain-shape vector quantization for audio coding

• US 9,009,036 B2
• Filed: 03/07/2012
• Issued: 04/14/2015
• Est. Priority Date: 03/07/2011
• Status: Active Grant

• Current Assignee: Xiph.Org Foundation
• Original Assignee: Xiph.Org Foundation
• Inventors: Valin, Jean-Marc, Terriberry, Timothy B.
• Primary Examiner(s): ALBERTALLI, BRIAN LOUIS
• Application Number:
  US13/414,490
• Publication Number:
  US 20120232913A1
• Time in Patent Office: 1,133 Days
• US Class Current: 704/230
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio

Abstract

Embodiments are generally directed to systems and methods for bit allocation and band partitioning for gain-shape vector quantization in an audio codec. An audio codec implements a method that uses an implicit, dynamic scheme to allow an encoder and decoder to recreate a series of bit allocation decisions for gain and shape without transmitting additional side information for each decision, based on the number of bits that are left remaining and available in a given packet. For implementation in practical codecs, the band comprising the allocation of bits for the shape is recursively split into equal partitions until the number of bits allocated to each partition is less than the maximum codebook size.

Claims

1. A computer-implemented method of coding an audio signal using gain-shape vector quantization, comprising:

organizing coefficients representing audio content into one or more bands;

dividing each band into a gain and a shape;

determining, in a processor-based device processing the audio content, a number of bits to use for the gain using an approximation method, wherein a size of a codebook dictates a total number of bits to allocate between the gain and the shape;

subtracting, in the processor-based device, the number of bits allocated to the gain from the total number of bits to determine a number of bits to allocate to the shape;

determining if the number of bits allocated to the shape is less than a defined maximum number of bits used in the codebook; and

recursively dividing the band into substantially equal size partitions until the number of bits allocated to the shape in each partition is less than the defined number.

2. The method of claim 1 wherein the coefficients are generated by a process selected from the group consisting of:

time-domain filtering, excitation of a Linear Predictive Coding (LPC) model, a subband filter process, and a modified discrete cosine transform function.

3. The method of claim 2 wherein the one or more bands are selected to be of a size that matches one or more properties of human hearing.

4. The method of claim 1 wherein the codebook comprises an algebraic codebook, and wherein the defined number of bits comprises 32 bits.

5. The method of claim 4 wherein the processor-based device comprises an audio codec having an encoder circuit and a decoder circuit.

6. The method of claim 5 wherein the encoder circuit executes an encoder process that makes a series of bit allocation decisions for the gain and the shape of the audio content, and wherein the decoder circuit executes a decoder process that recreates the series of bit allocation decisions for gain and shape, without requiring transmission of additional side information for each decision in any data packet transmitted between the encoder circuit and the decoder circuit.

7. The method of claim 1 wherein the gain is quantized using an A-law quantizer, and the shape is quantized using an optimal spherical quantizer, and wherein the approximation comprises an approximation for large factorials that approximates the size of the codebook to use for the gain, denoted N_g, as:

N_g≈

√

{square root over (C_gN)}2^b/N, wherein N is a number of dimensions, b is a target bitrate, and C_g is a defined constant that depends on the A-law quantizer parameter.

8. The method of claim 7 wherein the number of bits allocated for the gain is denoted b_g, and is calculated using the formula:

b_g=log₂ N_g.

9. The method of claim 8 further comprising determining the number of bits allocated for the gain using a low bitrate correction factor.

10. A computer-implemented method of coding an audio signal using gain-shape vector quantization, comprising:

organizing coefficients representing audio content into one or more bands;

dividing each band into a gain and a shape;

determining, in processor-based device processing the audio content, a number of bits to use for the gain using an approximation method for large factorials that approximates a size of a codebook to use for the gain, wherein the size of the codebook dictates a total number of bits to allocate between the gain and the shape;

subtracting, in the processor-based device, the number bits allocated to the gain from the total number of bits to determine a number of bits to allocate to the shape; and

quantizing the gain using an A-law quantizer, and quantizing the shape using an optimal spherical quantizer.

11. The method of claim 10 further comprising:

determining if the number of bits allocated to the shape is less than a defined number of bits used in the codebook; and

recursively dividing the band into equal size partitions until the number of bits allocated to the shape in each partition is less than the defined number.

12. The method of claim 11 wherein each partition is separated into gains denoted g₁ and g₂ and shapes denoted x₁ and x₂.

13. The method of claim 12 further comprising coding a relative magnitude of two partitions comprising a divided band using a scalar parameter denoted θ

, wherein a value of the scalar parameter is calculated by;

θ

=arctan(g₁/g₂).

14. The method of claim 13 wherein the codebook comprises an algebraic codebook, and wherein the defined number of bits comprises 32 bits.

15. The method of claim 14 wherein the processor-based device comprises an audio codec having an encoder circuit and a decoder circuit.

16. The method of claim 15 wherein the encoder circuit executes an encoder process that makes a series of bit allocation decisions for the gain and the shape of the audio content, and wherein the decoder circuit executes a decoder process that recreates the series of bit allocation decisions for gain and shape, without requiring transmission of additional side information for each decision in any data packet transmitted between the encoder circuit and the decoder circuit.

17. A system for coding an audio signal in an audio codec utilizing gain-shape vector quantization, comprising:

a first component organizing coefficients representing audio content into one or more bands and dividing each band into a gain and a shape;

a gain shape allocation component determining a number of bits to use for the gain using an approximation method, wherein the size of the codebook dictates a total number of bits to allocate between the gain and the shape, and subtracting, in the processor-based device, the number bits allocated to the gain from the total number of bits to determine a number of bits to allocate to the shape; and

a band partitioning and allocation component determining if the number of bits allocated to the shape is less than a defined maximum number of bits used in the codebook, and recursively dividing the band into substantially equal size partitions until the number of bits allocated to the shape in each partition is less than the defined number.

18. The system of claim 17 wherein the coefficients are generated by a process selected from the group consisting of:

time-domain filtering, excitation of a Linear Predictive Coding (LPC) model, a subband filter process, and a modified discrete cosine transform function.

19. The system of claim 18 wherein the codebook comprises an algebraic codebook, and wherein the defined number of bits comprises 32 bits.

20. The system of claim 19 wherein the system includes an audio codec having an encoder circuit and a decoder circuit, wherein the encoder circuit executes an encoder process that makes a series of bit allocation decisions for the gain and the shape of the audio content, and wherein the decoder circuit executes a decoder process that recreates the series of bit allocation decisions for gain and shape, without requiring transmission of additional side information for each decision in any data packet transmitted between the encoder circuit and the decoder circuit.

21. The system of claim 17 wherein the gain is quantized using an A-law quantizer, and the shape is quantized using an optimal spherical quantizer, and wherein the approximation comprises an approximation for large factorials that approximates the size of the codebook to use for the gain.