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1. (WO2007011749) FREQUENCY SEGMENTATION TO OBTAIN BANDS FOR EFFICIENT CODING OF DIGITAL MEDIA
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We claim:
1. An audio encoding method, comprising:
transforming an audio signal into spectral data (320);
coding a baseband portion of the spectral data (340);
in an extended band portion of the spectral data, determining characteristics of spectral data (360);
coding an altered configuration of sub-bands (360) comprising data indicating individual sub-bands in the extended band altered from an initial configuration.
2. The audio encoding method of claim 1 wherein the spectral data comprises coefficients in a transform domain and the altered configuration comprises difference values for sub-bands altered in size from the initial or default configuration.
3. The audio encoding method of claim 1 wherein the initial configuration is a uniform split configuration or a non-uniform split configuration.
4. The audio encoding method of claim 2 wherein a first bit is provided for coding whether a band configuration is default or optimized, and a second bit is provided for coding whether the initial configuration is the uniform split configuration or the nonuniform split configuration.
5. The audio encoding method of claim 1 wherein the altered configuration comprise sub-band multipliers that reflect the relative ratio of a sub-band size to the smallest sub-band size.
6. The audio encoding method of claim 1 wherein the altered configuration comprises sub-band multipliers reflecting splits and merges of sub-bands from the initial
configuration.
7. The audio encoding method of claim 1 wherein characteristics of spectral data comprise a measure of at least one of tonality, energy, or shape.
8. The audio encoding method of claim 1 wherein the initial configuration is altered at least in part based on tonality, and the method further comprises:
transforming the audio signal into fast fourier transform blocks;
time averaging adjacent fast fourier transform blocks;
determining a median filtered value by median filtering the time averaged adjacent fast fourier transform blocks;
comparing the time averaged adjacent fast fourier transform blocks to the median filtered value to obtain a tonality number;
determining a corresponding sub-band related to the adjacent fast fourier transform blocks; and assigning a tonal characteristic to the corresponding sub-band if the tonality number is above a threshold which can be represented by an absolute number, a given percentage of the median filtered value, or a percentage of a local standard deviation of the median filtered value.
9. The audio encoding method of claim 8 wherein the tonal characteristic is at least one of the factors used to determine whether or not to split or merge the corresponding sub-band.
10. The audio encoding method of claim 1 wherein a ratio of energy in
adjacent sub-bands is at least partially determinative of whether or not to alter the initial configuration.
11. The audio encoding method of claim 1 wherein sub-band shape differentiation is at least partially determinative of whether or not to split a sub-band.
12. The audio encoding method of claim 1 wherein a decision to split an individual sub-band into two sub-bands is at least partially made when the two split sub-bands have a means-square Euclidean difference that is lower than the individual sub-band by a threshold amount.
13. The audio encoding method of claim 1 wherein coding the altered configuration further comprises coding a minimum ratio sub-band size.
14. An output bit-stream created using the method of claim 1.
15. A decoder decoding an output of claim 1.
16. An audio decoding method, comprising:
decoding an encoded baseband (540);
decoding an encoded extended band comprising,
receiving data comprising a minimum ratio sub-band size and an altered configuration (545),
determining a smallest sub-band size in the altered configuration by
dividing the smallest sub-band size in the default configuration by the minimum ratio sub-band size (545), and
determining the actual sub-band multiplier by adding an expected sub-band multiplier to a coded difference value (545).
17. The audio decoding method of claim 16 wherein the initial configuration is a nonuniform split configuration.
18. The audio decoding method of claim 16 wherein for a second sub-band, data received indicates no alteration from the initial configuration and the second sub-band is decoded according to the initial configuration.

19. An audio encoder comprising:
a transformer (320) for transforming an audio signal into spectral data;
a base coder (340) for coding a baseband portion of the spectral data;
an extended band coder (350, 360) for,
configuring variable sized sub-bands based on characteristics of spectral data in an extended band (360),
coding difference values indicating how individual sub-bands differ in size from an initial configuration (360),
coding a minimum ratio sub-band size (360), and
coding sub-bands in the extended band (350).
20. The audio encoder of claim 19 wherein difference values are determined at least in part by sub-band split or merge from the initial configuration.