ENCODING METHOD, ENCODER, PERIODIC FEATURE AMOUNT DETERMINATION METHOD, PERIODIC FEATURE AMOUNT DETERMINATION APPARATUS, PROGRAM AND RECORDING MEDIUM

• US 20130311192A1
• Filed: 01/18/2012
• Published: 11/21/2013
• Est. Priority Date: 01/25/2011
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Moriya, Takehiro, Harada, Noboru, Hiwasaki, Yusuke, Kamamoto, Yutaka
• Granted Patent: US 9,711,158 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals

Abstract

An encoding technique encoding a sound signal at a low bit rate with reduced processing. The technique includes: an interval determination determining an interval T between samples corresponding to periodicity of an audio signal or an integer multiple of a fundamental frequency of the audio signal from a set S of candidates for the interval T; and a side information generating encoding the determined interval T to obtain side information. The interval determining determines the interval T from a set S of Y candidates (Y<Z) including Z₂ candidates (Z₂<Z) selected from among Z candidates for the interval T representable with the side information without depending on a candidate subjected to the interval determination in a previous frame a predetermined number of frames before the current frame and including a candidate subjected to the interval determination in the previous frame the predetermined number of frames before the current frame.

Claims

1. An encoding method for encoding a sample string in a frequency domain that is derived from an audio signal in frames, the method comprising:

an interval determination step of determining an interval T between samples from a set S of candidates for the interval T, the interval T corresponding to a periodicity of the audio signal or to an integer multiple of a fundamental frequency of the audio signal;

a side information generating step of encoding the interval T determined at the interval determination step to obtain side information; and

a sample string encoding step of encoding a rearranged sample to obtain a code string, the rearranged sample string

(1) including all of the samples in the sample string, and

(2) being a sample string in which at least some of the samples are rearranged so that all or some of one or a plurality of successive samples including a sample corresponding to the periodicity or the fundamental frequency of the audio signal in the sample string and one or a plurality of successive samples including a sample corresponding to an integer multiple of the periodicity or the fundamental frequency of the audio signal in the sample string are gathered together into a cluster on the basis of the interval T determined by the interval determination step;

wherein the interval determination step determines the interval T from a set S of candidates for the interval T, the set S being made up of Y candidates among Z candidates for the interval T, the Y candidates including Z₂ candidates selected without depending on a candidate subjected to the interval determination step in a previous frame a predetermined number of frames before the current frame and including a candidate subjected to the interval determination step in the previous frame the predetermined number of frames before the current frame, the Z candidates being representable with the side information, where Z₂<

Z and Y<

Z.

2. The encoding method according to claim 1,

wherein the interval determination step further comprises an adding step of adding to the set S a value adjacent to a candidate subjected to the interval determination step in a previous frame the predetermined number of frames before the current frame and/or a value having a predetermined difference from the candidate.

3. The encoding method according to claim 1 or 2,

wherein the interval determination step further comprises a preliminary selection step of selecting some of Z₁ candidates among the Z candidates for the interval T representable with the side information as the Z₂ candidates on the basis of an indicator obtainable from the audio signal and/or sample string in the current frame, where Z₂<

Z₁.

4. The encoding method according to claim 1 or 2,

wherein the interval determination step further comprises:

a preliminary selection step of selecting some of Z₁ candidates among the Z candidates for the interval T representable with the side information on the basis of an indicator obtainable from the audio signal and/or sample string in the current frame; and

a second adding step of selecting, as the Z₂ candidates, a set of a candidate selected at the preliminary selection step and a value adjacent to the candidate selected at the preliminary selection step and/or a value having a predetermined difference from the candidate selected at the preliminary selection step.

5. The encoding method according to claim 1 or 2,

wherein the interval determination step comprises:

a second preliminary selection step of selecting some of candidates for the interval T that are included in the set S on the basis of an indicator obtainable from the audio signal and/or sample string in the current frame; and

a final selection step of determining the interval T from a set made up of some of the candidates selected at the second preliminary selection step.

6. The encoding method according to claim 1,

wherein the greater an indicator indicating the degree of stationarity of the audio signal in the current frame, the greater the proportion of candidates subjected to the interval determination step in the previous frame the predetermined number of frames before the current frame to the set S is.

7. The encoding method according to claim 1,

wherein when the indicator indicating the degree of stationarity of the audio signal in the current frame is smaller than a predetermined threshold, only the Z₂ candidates are included in the set S.

8. The encoding method according to claim 6 or 7,

wherein the indicator indicating the degree of stationarity of the audio signal in the current frame increases when at least one of the conditions

(a-1) that a “

prediction gain of the audio signal in the current frame”

increases,

(a-2) that an “

estimated prediction gain of the audio signal in the current frame”

increases,

(b-1) that the difference between a “

prediction gain of the audio signal in the frame immediately preceding the current frame” and

the “

prediction gain of the audio signal in the current frame”

decreases,

(b-2) that the difference between an “

estimated prediction gain in the immediately preceding frame” and

the “

estimated prediction gain in the current frame”

decreases,

(c-1) that the “

sum of amplitudes of samples of the audio signal included in the current frame”

increases,

(c-2) that the “

sum of amplitudes of samples included in a sample string obtained by transforming a sample string of the audio signal included in the current frame into a frequency domain”

increases,

(d-1) that the difference between the “

sum of amplitudes of samples of the audio signal included in the immediately preceding frame” and

the “

sum of amplitudes of samples of the audio signal included in the current frame”

decreases,

(d-2) that the difference between the “

sum of amplitudes of samples included in a sample string obtained by transforming a sample string of the audio signal included in the immediately preceding frame into a frequency domain” and

the “

sum of amplitudes of samples included in a sample string obtained by transforming a sample string of the audio signal included in the current frame into a frequency domain”

decreases,

(e-1) that “

power of the audio signal in the current frame”

increases,

(e-2) that “

power of a sample string obtained by transforming a sample string of the audio signal in the current frame into a frequency domain”

increases,

(f-1) that the difference between “

power of the audio signal in the immediately preceding frame” and

“

power of the audio signal in the current frame”

decreases, and

(f-2) that the difference between “

power of a sample string obtained by transforming a sample string of the audio signal in the immediately preceding frame into a frequency domain” and

“

power of a sample string obtained by transforming a sample string of the audio signal in the current frame into a frequency domain”

decreases is satisfied.

9. The encoding method according to claim 1,

wherein the sample string encoding step comprises the step of outputting the code string obtained by encoding the sample string before being rearranged or the code string obtained by encoding the rearranged sample string and the side information, whichever has a smaller code amount.

10. The encoding method according to claim 1,

wherein the sample string encoding step

outputs the code string obtained by encoding the rearranged sample string and the side information when the sum of the code amount of or an estimated value of the code amount of the code string obtained by encoding the rearranged sample string and the code amount of the side information is smaller than the code amount of or an estimated value of the code amount of the code string obtained by encoding the sample string before being rearranged, and

outputs the code string obtained by encoding the sample string before being rearranged when the code amount of or an estimated value of the code amount of the code string obtained by encoding the sample string before being rearranged is smaller than the sum of the code amount of or an estimated value of the code amount of the code string obtained by encoding the rearranged sample string and the code amount of the side information.

11. The encoding method according to claim 9 or 10,

wherein the proportion of candidates subjected to the interval determination step in the previous frame the predetermined number of frames before the current frame to the set S is greater when a code string output in the immediately preceding frame is a code string obtained by encoding a rearranged sample string than when a code string output in the immediately preceding frame is a code string obtained by encoding a sample string before being rearranged.

12. The encoding method according to claim 9 or 10,

wherein when a code string output in the immediately preceding frame is a code string obtained by encoding a sample string before being rearranged, the set S includes only the Z₂ candidates.

13. The encoding method according to claim 9 or 10,

wherein when the current frame is a temporally first frame, or when the immediately preceding frame is coded by an encoding method different from the encoding method, or when a code string output in the immediately preceding frame is a code string obtained by encoding a sample string before being rearranged, the set S includes only the Z₂ candidates.

23. A non-transitory computer-readable recording medium having recorded thereon a computer program for causing a computer to execute the encoding method according to claim 1 or the periodic feature amount determination method according to claim 14.

24. A computer program for causing a computer to execute the steps of the encoding method according to claim 1 or the periodic feature amount determination method according to claim 14.

14. A method for determining a periodic feature amount of an audio signal in frames, the method comprising:

a periodic feature amount determination step of determining a periodic feature amount of the audio signal from a set of candidates for the periodic feature amount on a frame-by-frame basis; and

a side information generating step of encoding the periodic feature amount obtained at the periodic feature amount determination step to obtain side information;

wherein the periodic feature amount determination step determines a periodic feature amount from a set S of candidates for the periodic feature amount, the set S being made up of Y candidates among Z candidates for the periodic feature amount, the Y candidates including Z₂ candidates selected without depending on a candidate subjected to the periodic feature amount determination step in a previous frame a predetermined number of frames before the current frame and including a candidate subjected to the periodic feature amount determination step in the previous frame the predetermined number of frames before the current frame, the Z candidates being representable with the side information, where Z₂<

Z and Y<

Z.

15. The periodic feature amount determination method according to claim 14,

wherein the periodic feature amount determination step further comprises an adding step of adding to the set S a value adjacent to a candidate subjected to the periodic feature amount determination step in a previous frame the predetermined number of frames before the current frame and/or a value having a predetermined difference from the candidate.

16. The periodic feature amount determination method according to claim 14,

wherein the greater an indicator indicating the degree of stationarity of the audio signal in the current frame, the greater the proportion of candidates subjected to the periodic feature determination step in the previous frame the predetermined number of frames before the current frame to the set S is.

17. The periodic feature amount determination method according to claim 16,

wherein when the indicator indicating the degree of stationarity of the audio signal in the current frame is smaller than a predetermined threshold, only the Z₂ candidates are included in the set S.

18. The periodic feature amount determination method according to claim 16 or 17,

wherein the indicator indicating the degree of stationarity of the audio signal in the current frame increases when at least one of the conditions

(a-1) that a “

prediction gain of the audio signal in the current frame”

increases,

(a-2) that an “

estimated prediction gain of the audio signal in the current frame”

increases,

(b-1) that the difference between a “

prediction gain of the audio signal in the frame immediately preceding the current frame” and

the “

prediction gain of the audio signal in the current frame”

decreases,

(b-2) that the difference between an “

estimated prediction gain in the immediately preceding frame” and

the “

estimated prediction gain in the current frame”

decreases,

(c-1) that the “

sum of amplitudes of samples of the audio signal included in the current frame”

increases,

(c-2) that the “

sum of amplitudes of samples included in a sample string obtained by transforming a sample string of the audio signal included in the current frame into a frequency domain”

increases,

(d-1) that the difference between the “

sum of amplitudes of samples of the audio signal included in the immediately preceding frame” and

the “

sum of amplitudes of samples of the audio signal included in the current frame”

decreases,

(d-2) that the difference between the “

sum of amplitudes of samples included in a sample string obtained by transforming a sample string of the audio signal included in the immediately preceding frame into a frequency domain” and

the “

sum of amplitudes of samples included in a sample string obtained by transforming a sample string of the audio signal included in the current frame into a frequency domain”

decreases,

(e-1) that “

power of the audio signal in the current frame”

increases,

(e-2) that “

power of a sample string obtained by transforming a sample string of the audio signal in the current frame into a frequency domain”

increases,

(f-1) that the difference between “

power of the audio signal in the immediately preceding frame” and

“

power of the audio signal in the current frame”

decreases, and

(f-2) that the difference between “

power of a sample string obtained by transforming a sample string of the audio signal in the immediately preceding frame into a frequency domain” and

“

power of a sample string obtained by transforming a sample string of the audio signal in the current frame into a frequency domain”

decreases

is satisfied.

19. A encoder encoding a sample string in a frequency domain that is derived from an audio signal in frames, the encoder comprising:

an interval determination unit determining an interval T between samples from a set S of candidates for the interval T, the interval T corresponding to a periodicity of the audio signal or to an integer multiple of a fundamental frequency of the audio signal;

a side information generating unit encoding the interval T determined by the interval determination unit to obtain side information; and

a sample string encoding unit encoding a rearranged sample string to obtain a code string, the rearranged sample string

(1) including all of the samples in the sample string, and

(2) being a sample string in which at least some of the samples are rearranged so that all or some of one or a plurality of successive samples including a sample corresponding to the periodicity or the fundamental frequency of the audio signal in the sample string and one or a plurality of successive samples including a sample corresponding to an integer multiple of the periodicity or the fundamental frequency of the audio signal in the sample string are gathered together into a cluster on the basis of the interval T determined by the interval determination unit;

wherein the interval determination unit determines the interval T from a set S of candidates for the interval T, the set S being made up of Y candidates among Z candidates for the interval T, the Y candidates including Z₂ candidates selected without depending on a candidate subjected to processing by the interval determination unit in a previous frame a predetermined number of frames before the current frame and including a candidate subjected to the processing by the interval determination unit in the previous frame the predetermined number of frames before the current frame, the Z candidates being representable with the side information, where Z₂<

Z and Y<

Z.

20. The encoder according to claim 19,

wherein the sample string encoding unit

outputs the code string obtained by encoding the rearranged sample string and the side information when the sum of the code amount of or an estimated value of the code amount of the code string obtained by encoding the rearranged sample string and the code amount of the side information is smaller than the code amount of or an estimated value of the code amount of the code string obtained by encoding the sample string before being rearranged, and

outputs the code string obtained by encoding the sample string before being rearranged when the code amount of or an estimated value of the code amount of the code string obtained by encoding the sample string before being rearranged is smaller than the sum of the code amount of or an estimated value of the code amount of the code string obtained by encoding the rearranged sample string and the code amount of the side information.

21. A periodic feature amount determination apparatus determining a periodic feature amount of an audio signal in frames, the apparatus comprising:

a periodic feature amount determination unit of determining a periodic feature amount of the audio signal from a set of candidates for the periodic feature amount on a frame-by-frame basis; and

a side information generating unit of encoding the periodic feature amount obtained at the periodic feature amount determination unit to obtain side information;

wherein the periodic feature amount determination unit determines a periodic feature amount from a set S of candidates for the periodic feature amount, the set S being made up of Y candidates among Z candidates for the periodic feature amount, the Y candidates including Z₂ candidates selected without depending on a candidate subjected to the periodic feature amount determination unit in a previous frame a predetermined number of frames before the current frame and including a candidate subjected to the periodic feature amount determination unit in the previous frame the predetermined number of frames before the current frame, the Z candidates being representable with the side information, where Z₂<

Z and Y<

Z.

22. (canceled)