Quality and rate control strategy for digital audio

• US 20060053020A1
• Filed: 10/26/2005
• Published: 03/09/2006
• Est. Priority Date: 12/14/2001
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Lee, Ming-Chieh, Thumpudi, Naveen, Chen, Wei-Ge
• Granted Patent: US 7,340,394 B2
• Time in Patent Office: Days
• US Class Current: 704/503
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding

Abstract

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.

Claims

1. A computer-readable medium encoded with computer-executable instructions for causing a computer programmed thereby to perform a method of controlling quality of information in a constant bitrate encoder, wherein the encoder outputs the information at variable quality and compressed to a constant or relatively constant bitrate, the method comprising:

quantizing a current block of information to meet constant or relatively constant bitrate requirements, wherein the encoder adjusts quantization step size of the quantizing in view of a comparison of a target quality parameter for the current block to a quality measurement for the current block as quantized and reconstructed, thereby reducing number of changes in quality and smoothing transitions between the changes in quality; and

entropy coding the quantized current block of information.

2. The computer-readable medium of claim 1 wherein the encoder adjusts the quantization step size also in view of a target minimum-bits parameter and a target maximum-bits parameter.

3. The computer-readable medium of claim 1 wherein the encoder adjusts the quantization step size also in view of one or more complexity estimates and one or more complexity estimate noise measures.

4. The computer-readable medium of claim 1 wherein the current block has a block size selected from among plural available block sizes, wherein the encoder adjusts the quantization step size also in view of a value of control parameter for the current block, and wherein the encoder normalizes block size when computing the value.

5. The computer-readable medium of claim 1 wherein the encoder adjusts the quantization step size in a quality control quantization loop and in a bit-count control quantization loop following and de-linked from the quality control quantization loop.

6. The computer-readable medium of claim 5 wherein the encoder adjusts the quantization step size by different rules in the quality control quantization loop and the bit-count control quantization loop.

7. The computer-readable medium of claim 1 wherein the encoder accounts for non-monotonicity of quality as a function of quantization step size when the encoder adjusts the quantization step size.

8. The computer-readable medium of claim 1 wherein the encoder adjusts the quantization step size also in view of a value of control parameter for the current block, and wherein the encoder lowpass filters the value as part of a series of values.

9. The computer-readable medium of claim 1 wherein the encoder adjusts the quantization step size also in view of a value of control parameter for the current block, and wherein the encoder computes the value to correct bias in a model that relates quality and bitrate or bit count to quantization step size.

10. In a spectral audio encoder, a computer-implemented method comprising:

performing a frequency transform on plural time domain audio samples to produce a current block of frequency coefficients; and

compressing the current block of frequency coefficients, wherein the compressing includes,

quantizing the current block of frequency coefficients;

comparing a quality measure for the current block to a quality target; and

comparing a bit-count measure for the current block to a minimum-bits target and to a maximum-bits target.

13. The method of claim 10 wherein the quality target, the minimum-bits target, and the maximum-bits target are for the current block.

11. (canceled)

12. (canceled)

14. A computer-readable medium encoded with computer-executable instructions for causing a computer programmed thereby to perform a method of controlling quality and bitrate in an audio encoder, the method comprising:

determining one or more target quality parameters, a first target quality parameter of the one or more target quality parameters indicating an acceptable audio quality;

determining plural target bitrate parameters, a first target bitrate parameter of the plural target bitrate parameters indicating a minimum acceptable number of bits produced, and a second target bitrate parameter of the plural target bitrate parameters indicating a maximum acceptable number of bits produced; and

compressing current audio information, wherein quantization of the current audio information is based at least in part upon one or more comparisons of measures for the current audio information to the first target quality parameter, the first target bitrate parameter, and the second target bitrate parameter.

15. The computer-readable medium of claim 14 wherein the method further comprises performing a frequency transform on plural time domain audio samples, producing a current block of frequency coefficients, and wherein the current audio information is the current block of frequency coefficients.

16. The computer-readable medium of claim 15 wherein the first target quality parameter, the first target bitrate parameter, and the second target bitrate parameter are for the current block.

17. The computer-readable medium of claim 14 wherein the compressing includes:

quantizing the current audio information;

computing a quality measure based upon the quantized audio information; and

comparing the quality measure to the first target quality parameter.

18. The computer-readable medium of claim 14 wherein the compressing includes:

quantizing the current audio information;

entropy encoding the quantized audio information;

computing a bit-count measure based upon the entropy encoded audio information; and

comparing the bit-count measure to the first and second target bitrate parameters.

19. The computer-readable medium of claim 14 wherein the compressing includes:

in a first quantization loop, adjusting the quantization until satisfaction of the first target quality parameter; and

in a second quantization loop, adjusting the quantization until satisfaction of the first and second target bitrate parameters.

20. The computer-readable medium of claim 14 wherein the first target bitrate parameter is a function of factors comprising an average bit count estimate, buffer fullness, and buffer sweet spot.

21. The computer-readable medium of claim 14 wherein the second target bitrate parameter is a function of factors comprising an average bit count estimate, buffer fullness, and buffer sweet spot.

22. The computer-readable medium of claim 14 wherein the first target quality parameter is a function of factors comprising a complexity estimate and goal bit count.

23-100. -100. (canceled)