Method of encoding an audio signal using a quality value for bit allocation

• US 7,003,449 B1
• Filed: 10/30/1999
• Issued: 02/21/2006
• Est. Priority Date: 10/30/1999
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Inventors: George, Sapna, Absar, Mohammed Javed
• Primary Examiner(s): Knepper, David D.
• Application Number:
  US10/129,045
• Time in Patent Office: 2,306 Days
• Field of Search: 704200-201, 704/229, 704/230, 704/500
• US Class Current: 704/200.1
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/035 Scalar quantisation

Abstract

A method for encoding an audio signal, including providing a masking function, representative of psychoacoustic masking; setting a quality value for data of the encoded signal, adjusting the masking function dependent upon the quality value; and allocating bits for quantization of the encoded signal based on the incremental masking function.

Claims

1. A method for encoding an input audio signal to produce an encoded audio signal, comprising;

providing a masking function, representative of psychoacoustic masking;

setting a quality value for data of the encoded audio signal,

adjusting the masking function dependent upon the quality value; and

allocating bits for quantization of the encoded audio signal based on the adjusted masking function.

2. A method as claimed in claim 1, wherein the quality value represents an average weighted noise-to-mask ratio (AWNMR).

3. A method as claimed in claim 2, wherein the quality value is equated to a variable θ

, such that $\mathrm{AWNMR}<br><br>\left(\mathrm{dB}\right)\ge <br><br>\frac{20}{N}<br><br>\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>\left[{\log }_{10}<br><br>\left(\frac{2^{2<br><br>\left({\tilde{S}}_v/128-24\right)}}{3·<br><br>2^{2<br><br>\left(S_v/128-24\right)}}\right)+\frac{w_k}{20}\right]=\frac{20}{N}<br><br>\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>\left[{\log }_{10}<br><br>\left(\frac{2^{\left({\stackrel{\_}{S}}_v-S_v\right)/64}}{3}\right)+\frac{w_k}{20}\right]=\mathrm{\theta <br><br>}<br><br>\left(\mathrm{snroffst}\right)$

where

S_v is the masking function,

{tilde over (S)}_v is the adjusted masking function,

W_k is a weighted function, and

snroffst is a variable proportion to the signal to mask ratio.

4. A method as claimed in claim 3, further comprising:

deriving transformation coefficients from input audio signal for encoding; and

mapping the transform coefficients to a power spectrum density function (PSD), wherein the bit allocation is determined by differencing the PSD and the adjusted masking function.

5. A method as claimed in claim 3, further comprising:

dividing the input audio signal into a plurality of frames, for carrying quantization bits and signal data; and

increasing or decreasing a frame length of one of the frames until the frame accommodates the quantization bits.

6. A method as claimed in claim 1, wherein transform coefficients are derived from the input audio signal for encoding and are mapped to a power spectrum density function (PSD) and wherein the bit allocation is determined by differencing the PSD and the adjusted masking function.

7. A method as claimed in claim 6, further comprising:

dividing the input audio signal into a plurality of frames, for carrying quantization bits and other signal data; and

increasing or decreasing a frame length of one of the frames until the frame accommodates the quantization bits.

8. A method as claimed in claim 1, wherein encoding the input audio signal includes dividing the signal into a plurality of frames, for carrying quantizsation and other signal data, and increasing or decreasing one or more frame lengths until the associated frame accommodates the bits allocated for quantization.

9. A method as claimed in claim 1, wherein the adjusting of the masking function is dependent upon the quality value and the input audio signal.

10. A method as claimed in claim 1, wherein the encoded audio signal comprises an AC-3 signal.

11. A method as claimed in claim 1, wherein the encoded audio signal is compressed at a compression ratio, wherein the compression ratio is variable, and the compression ratio is determined by the quality value and the input audio signal.

12. A method as claimed in claim 11, wherein the input audio signal has a complexity in a frequency domain, and the compression ratio is dependent upon the complexity of the input audio signal.

13. A method for encoding an input audio signal to produce a constant quality encoded audio signal, comprising;

dividing the input audio signal into one or more frames;

providing a masking function, representative of psychoacoustic masking;

providing a quality value for data of the encoded audio signal, wherein the quality value is held constant;

determining a frame length required to encode each frame at the quality value;

adjusting the masking function dependent upon the frame length of each frame; and

allocating bits within each frame for quantization of the encoded audio signal dependent upon the adjusted masking function.

14. A method as claimed in claim 13, wherein the frame length is dependent upon the quality value and the input audio signal.

15. A method as claimed in claim 13, wherein the encoded audio signal is compressed at a compression ratio, wherein the compression ratio is variable, and the compression ratio is determined by the quality value and the input audio signal.

16. A method as claimed in claim 15, wherein the input audio signal has a complexity in a frequency domain, and the compression ratio is dependent upon the complexity of the input audio signal.

17. A method as claimed in claim 16, wherein the quality value represents an average weighted noise-to-mask ratio (AWNMR).

18. A method as claimed in claim 16, wherein the quality value is equated to a variable θ

, such that $\mathrm{AWNMR}<br><br>\left(\mathrm{dB}\right)\ge <br><br>\frac{20}{N}<br><br>\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>\left[{\log }_{10}<br><br>\left(\frac{2^{2<br><br>\left({\tilde{S}}_v/128-24\right)}}{3·<br><br>2^{2<br><br>\left(S_v/128-24\right)}}\right)+\frac{w_k}{20}\right]=\frac{20}{N}<br><br>\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>\left[{\log }_{10}<br><br>\left(\frac{2^{\left({\stackrel{\_}{S}}_v-S_v\right)/64}}{3}\right)+\frac{w_k}{20}\right]=\mathrm{\theta <br><br>}<br><br>\left(\mathrm{snroffst}\right)$

where

S_v is the masking function,

{tilde over (S)}_v is the adjusted masking function,

W_k is a weighted function, and

snroffst is a variable proportion to the signal to mask ratio.

19. A method as claimed in claim 16, wherein the encoded audio signal comprises an AC-3 signal.

20. A method as claimed in claim 19, wherein the quality value represents an approximation of the average weighted noise-to-mask ratio (AWNMR).