Accounting for non-monotonicity of quality as a function of quantization in quality and rate control for digital audio
View Patent ↗An audio encoder regulates quality and bitrate with a control strategy. The strategy includes several features. First, an encoder regulates quantization using quality, minimum bit count, and maximum bit count parameters. Second, an encoder regulates quantization using a noise measure that indicates reliability of a complexity measure. Third, an encoder normalizes a control parameter value according to block size for a variable-size block. Fourth, an encoder uses a bit-count control loop de-linked from a quality control loop. Fifth, an encoder addresses non-monotonicity of quality measurement as a function of quantization level when selecting a quantization level. Sixth, an encoder uses particular interpolation rules to find a quantization level in a quality or bit-count control loop. Seventh, an encoder filters a control parameter value to smooth quality. Eighth, an encoder corrects model bias by adjusting a control parameter value in view of current buffer fullness.
1. A computer-readable storage medium encoded with computer-executable instructions for causing a computer programmed thereby to perform a method comprising:
selecting a quantization level within a range of quantization levels, wherein the selecting accounts for non-monotonicity of quality measure as a function of quantization level within the range; and
quantizing audio information by the quantization level.
2. The computer-readable storage medium of claim 1 wherein the audio information is a block of frequency coefficients, and wherein the quantization level is a quantization step size.
3. The computer-readable storage medium of claim 1 wherein the method further comprises:
computing a first quality measure indicating quality of the audio information as quantized by the quantization level;
comparing the first quality measure to a second quality measure for the audio information, the second qualitymeasure indicating quality of the audio information as quantized by a previous quantization level higher than the quantization level; and
if the first quality measure indicates worse quality than the second quality measure, designating the quantization level as inferior.
4. The computer-readable storage medium of claim 3 wherein,
when accounting for non-monotonicity, the selecting includes evaluating each of plural quantization levels within a range of quantization levels, and wherein the selecting otherwise includes replacing the range with a sub-range of the range and evaluating a quantization level within the sub-range.
5. The computer-readable storage medium of claim 1 wherein the method further comprises, in a quality control loop, setting a target quality, the quality control loop including the selecting and the quantizing.
6. The computer-readable storage medium of claim 5 wherein the method further comprises, in a rate control loop, setting a target bit rate and adjusting quantization of the audio information in view of the target bit rate.
7. The computer-readable storage medium of claim 1 wherein the selecting considers a target quality but not a bit rate associated with the quantization level.
8. The computer-readable storage medium of claim 1 wherein the method further comprises:
computing a first quality measure indicating quality of the audio information as quantized by the quantization level;
comparing the first quality measure to a second quality measure for the audio information, the second quality measure indicating quality of the audio information as quantized by a previous quantization level lower than the quantization level; and
if the second quality measure indicates worse quality than the first quality measure, designating the previous quantization level as inferior.
9. The computer-readable storage medium of claim 8 , wherein the first quality measure and the second quality measure are noise to excitation ratios.
10. A computer-readable storage medium encoded with computer-executable instructions for causing a computer programmed thereby to perform a method comprising:
quantizing audio information by a quantization level;
computing a first quality measure indicating quality of the audio information as quantized by the quantization level;
comparing the first quality measure to a second quality measure for the audio information, the second quality measure indicating quality of the audio information as quantized by a previous quantization level; and
if the comparing indicates non-monotonicity of quality measure as a function of quantization level, designating the quantization level as inferior.
11. The computer-readable storage medium of claim 10 wherein the audio information is a block of frequency coefficients, and wherein the quantization level is a quantization step size.
12. The computer-readable storage medium of claim 10 , wherein the method further comprises, in a quality control loop, setting a target quality, the quality control loop including the quantizing, the computing the first quality measure and the comparing.
13. The computer-readable storage medium of claim 10 wherein the computing the first quality measure considers a target quality but not a bit rate associated with the quantization level.
14. The computer-readable storage medium of claim 10 wherein the first quality measure and the second quality measure are noise to excitation ratios.
15. In an audio encoder, a method comprising:
receiving audio information;
quantizing and entropy coding the audio information including:
selecting a quantization level within a range of quantization levels, wherein the selecting accounts for non-monotonicity of quality measure as a function of quantization level within the range; and
applying the quantization level to the audio information for the quantizing; outputting the entropy coded, quantized audio information.
16. The method of claim 15 wherein the audio information is a block of frequency coefficients, and wherein the quantization level is a quantization step size.
17. The method of claim 15 further comprising:
computing a first quality measure indicating quality of the audio information as quantized by the quantization level;
comparing the first quality measure to a second quality measure for the audio information, the second quality measure indicating quality of the audio information as quantized by a previous quantization level higher than the quantization level; and
if the first quality measure indicates worse quality than the second quality measure, designating the quantization level as inferior.
18. The method of claim 15 further comprising, in a quality control loop, setting a target quality, the quality control loop including the selecting and the quantizing.
19. The method of claim 18 further comprising, in a rate control loop, setting a target bit rate and adjusting quantization of the audio information in view of the target bit rate.
20. The method of claim 15 wherein the selecting considers a target quality but not a bit rate associated with the quantization level.