Method, apparatus, and system for efficient rate control in audio encoding

• US 6,732,071 B2
• Filed: 09/27/2001
• Issued: 05/04/2004
• Est. Priority Date: 09/27/2001
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: VanDeusen, Mark P., Lopez-Estrada, Alex A.
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): PATEL, KINARI M
• Application Number:
  US09/967,440
• Publication Number:
  US 20030083867A1
• Time in Patent Office: 950 Days
• Field of Search: 704/200.1, 704/219, 704/222, 704/225, 704/229, 704/230
• US Class Current: 704/219
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders

Abstract

According to one aspect of the invention, a method is provided in which audio samples representing an input audio signal are received. The input audio samples are transformed into a vector of spectral values in a frequency domain. A value of a quantizing parameter is determined that satisfies one or more criteria based, at least in part, on a modified Newtonian search process, the determined value of the quantizing parameter being used to quantize the respective vector of spectral values to generate a vector of quantized values.

Claims

1. A method comprising:

receiving audio samples representing an input audio signal;

transforming the input audio samples into a vector of spectral values in a frequency domain; and

determining a value of a quantizing parameter that satisfies one or more criteria based, at least in part, on a modified Newtonian search process, the determined value of the quantizing parameter being used to quantize the respective vector of spectral values to generate a vector of quantized values, the value of the quantizing parameter being determined according to the following formula;

$\mathrm{global\_gain}\ge <br><br>\lceil <br><br>A·<br><br>{\log }_2<br><br>\left(\frac{\mathrm{MAX}<br><br><br><br>x_r<br><br>\left(i\right)<br><br>}{{\left[B-C\right]}^D}\right)\rceil <br><br>$

wherein global gain corresponds to the value of the quantizing parameter, A corresponds to a first constant, xr(i) corresponds to an original spectral value for frequency line i, B corresponds to a second constant representing a maximum quantized spectral value, C corresponds to a third constant, and D corresponds to a fourth constant.

2. The method of claim 1 wherein determining the value of the quantizing parameter includes:

determining the value of the quantizing parameter such that a maximum quantized value does not exceed a maximum index of one or more corresponding codebooks.

3. The method of claim 2 wherein the one or more codebooks are used to requantize the quantized values.

4. The method of claim 3 wherein the one or more codebooks are Huffman code tables.

5. The method of claim 1 wherein determining the value of the quantizing parameter includes:

determining the value of the quantizing parameter based on the modified Newtonian search process such that a total number of bits used for encoding the vector of quantized values does not exceed a maximum number of bits available for encoding the vector of the quantized values.

6. The method of claim 5 including:

computing a first estimate and a second estimate for the quantizing parameter; and

performing a set of operations iteratively until a predetermined number of iterations is reached, including;

deriving a new estimate for the quantizing parameter based on the previous estimates for the quantizing parameter.

7. The method of claim 6 wherein deriving the new estimate includes:

calculating a line tangent to a function representing the total number of bits used based on the previous estimates; and

calculating the new estimate based on an intercept between the line tangent calculated and a line representing the maximum number of bits available.

8. The method of claim 6 wherein performing the set of operations further including:

determining whether the total number of bits based upon the new estimate exceeds the maximum number of bits available;

if the total number of bits based upon the new estimate exceeds the maximum number of bits available, increasing the new estimate by a first factor; and

if the total number of bits based upon the new estimate does not exceed the maximum number of bits available, decreasing the new estimate by a second factor.

9. The method of claim 8 wherein the first factor and second factor are integer values.

10. The method of claim 6 wherein the value of the quantizing parameter determined with respect to one block of spectral values is stored in memory and used as an initial estimate for a next block of spectral values.

11. An apparatus comprising:

logic to receive input audio samples representing corresponding input audio signals;

logic to transform the input audio samples into a vector of spectral values in a frequency domain; and

logic to determine a value of a quantizing parameter that satisfies one or more criteria based, at least in part, on a modified Newtonian search process, the determined value of the quantizing parameter being used to quantize the respective vector of spectral values to generate a vector of quantized values;

logic to compute the value of the quantizing parameter such that a maximum quantized value does not exceed a maximum index of one or more corresponding codebooks, based upon the following formula;

$\mathrm{global\_gain}\ge <br><br>\lceil <br><br>A·<br><br>{\log }_2<br><br>\left(\frac{\mathrm{MAX}<br><br><br><br>x_r<br><br>\left(i\right)<br><br>}{{\left[B-C\right]}^D}\right)\rceil <br><br>$

wherein global gain corresponds to the value of the quantizing parameter, A corresponds to a first constant, xr(i) corresponds to an original spectral value for frequency line i, B corresponds to a second constant representing a maximum quantized spectral value, C corresponds to a third constant, and D corresponds to a fourth constant.

12. The apparatus of claim 11 wherein logic to determine the value of the quantizing parameter includes:

logic to determine the value of the quantizing parameter based on the modified Newtonian search process such that a total number of bits used for encoding the vector of quantized values does not exceed a maximum number of bits available for encoding the vector of the quantized values.

13. The apparatus of claim 12 including:

logic to compute a first estimate and a second estimate for the quantizing parameter; and

logic to perform a set of operations iteratively until a predetermined number of iterations is reached, including;

logic to derive a new estimate for the quantizing parameter based on the previous estimates for the quantizing parameter.

14. The apparatus of claim 13 wherein logic to derive the new estimate including:

logic to calculate a line tangent to a function representing the total number of bits used based on the previous estimates; and

logic to calculate the new estimate based on an intercept between the line tangent calculated and a line representing the maximum number of bits available.

15. The apparatus of claim 14 wherein logic to perform the set of operations further including:

logic to determine whether the total number of bits based upon the new estimate exceeds the maximum number of bits available;

logic to increase the new estimate by a first integer if the total number of bits based upon the new estimate exceeds the maximum number of bits available; and

logic to decrease the new estimate by a second integer if the total number of bits based upon the new estimate does not exceed the maximum number of bits available.

16. A system comprising:

a transformation unit to transform input audio samples representing corresponding audio signals into a vector of spectral values in a frequency domain;

a psychoacoustic modeling unit to analyze the input audio samples and generate a frequency mask; and

a bit allocator and quantizer unit coupled to the transformation unit and the psychoacoustic unit, the bit allocator and quantizer unit including;

logic to determine a value of a quantizing parameter that satisfies one or more criteria based, at least in part, on a modified Newtonian search process, the determined value of the quantizing parameter being used to quantize the respective vector of spectral values to generate a vector of quantized values;

logic to compute the value of the quantizing parameter such that a maximum quantized value does not exceed a maximum index of one or more corresponding codebooks, based upon the following formula;

$\mathrm{global\_gain}\ge <br><br>\lceil <br><br>A·<br><br>{\log }_2<br><br>\left(\frac{\mathrm{MAX}<br><br><br><br>x_r<br><br>\left(i\right)<br><br>}{{\left[B-C\right]}^D}\right)\rceil <br><br>$

wherein global gain corresponds to the value of the quantizing parameter, A corresponds to a first constant, xr(i) corresponds to an original spectral value for frequency line i, B corresponds to a second constant representing a maximum quantized spectral value, C corresponds to a third constant, and D corresponds to a fourth constant.

17. The system of claim 16 wherein logic to determine the value of the quantizing parameter includes:

logic to determine the value of the quantizing parameter based on the modified Newtonian search process such that a total number of bits used for encoding the vector of quantized values does not exceed a maximum number of bits available for encoding the vector of the quantized values.

18. The system of claim 17 including:

logic to compute a first estimate and a second estimate for the quantizing parameter; and

logic to perform a set of operations iteratively until a predetermined number of iterations is reached, including;

logic to derive a new estimate for the quantizing parameter based on the previous estimates for the quantizing parameter.

19. The system of claim 18 wherein logic to derive the new estimate including:

logic to calculate a line tangent to a function representing the total number of bits used based on the previous estimates; and

logic to calculate the new estimate based on an intercept between the line tangent calculated and a line representing the maximum number of bits available.

20. The system of claim 19 wherein logic to perform the set of operations further including:

logic to determine whether the total number of bits based upon the new estimate exceeds the maximum number of bits available;

logic to increase the new estimate by a first integer if the total number of bits based upon the new estimate exceeds the maximum number of bits available; and

logic to decrease the new estimate by a second integer if the total number of bits based upon the new estimate does not exceed the maximum number of bits available.

21. A machine-readable medium comprising instructions which, when executed by a machine, cause the machine to perform operations including:

receiving audio samples representing an input audio signal;

transforming the input audio samples into a vector of spectral values in a frequency domain; and

determining a value of a quantizing parameter that satisfies one or more criteria based, at least in part, on a modified Newtonian search process, the determined value of the quantizing parameter being used to quantize the respective vector of spectral values to generate a vector of quantized value, the value of the quantizing parameter being determined such that a maximum quantized value does not exceed a maximum index of one or more corresponding codebooks according to the following formula;

$\mathrm{global\_gain}\ge <br><br>\lceil <br><br>A·<br><br>{\log }_2<br><br>\left(\frac{\mathrm{MAX}<br><br><br><br>x_r<br><br>\left(i\right)<br><br>}{{\left[B-C\right]}^D}\right)\rceil <br><br>$

wherein global gain corresponds to the value of the quantizing parameter, A corresponds to a first constant, xr(i) corresponds to an original spectral value for frequency line i, B corresponds to a second constant representing a maximum quantized spectral value, C corresponds to a third constant, and D corresponds to a fourth constant.

22. The machine-readable medium of claim 21 wherein determining the value of the quantizing parameter includes:

determining the value of the quantizing parameter based on the modified Newtonian search process such that a total number of bits used for encoding the vector of quantized values does not exceed a maximum number of bits available for encoding the vector of the quantized values.

23. The machine-readable medium of claim 22 including:

computing a first estimate and a second estimate for the quantizing parameter; and

performing a set of operations iteratively until a predetermined number of iterations is reached, including;

deriving a new estimate for the quantizing parameter based on the previous estimates for the quantizing parameter.

24. The machine-readable medium of claim 23 wherein deriving the new estimate includes:

calculating a line tangent to a function representing the total number of bits used based on the previous estimates; and

calculating the new estimate based on an intercept between the line tangent calculated and a line representing the maximum number of bits available.

25. The machine-readable medium of claim 24 wherein performing the set of operations further including:

determining whether the total number of bits based upon the new estimate exceeds the maximum number of bits available;

if the total number of bits based upon the new estimate exceeds the maximum number of bits available, increasing the new estimate by a first factor; and

if the total number of bits based upon the new estimate does not exceed the maximum number of bits available, decreasing the new estimate by a second factor.