Encoding method, encoder, periodic feature amount determination method, periodic feature amount determination apparatus, program and recording medium

Patent metadata

Field	Value
Publication number	US-9711158-B2
Application number	US-201213981125-A
Country	US
Kind code	B2
Filing date	Jan 18, 2012
Priority date	Jan 25, 2011
Publication date	Jul 18, 2017
Grant date	Jul 18, 2017

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 Z 2 candidates (Z 2 <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.

First claim

What is claimed is:

1. A computer-implemented encoding method for encoding a sample string in a frequency domain that is derived from an audio signal in frames, executing on a processor, the method comprising:
a step of receiving the sample string of the audio signal in the time-domain;
a step of transforming the audio signal in the time-domain to the frequency-domain;
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;
outputting the side information to a decoder;
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 Z 2 candidates selected without depending on a previous candidate for the interval T corresponding to a periodicity of the audio signal or to an integer multiple of a fundamental frequency of the audio signal, the previous candidate subjected to the interval determination step in a previous frame a predetermined number of frames before the current frame and including the previous 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 Z 2 <Z and Y<Z; and
outputting the code string to the decoder, wherein the code string has a compressed amount of data compared to the received sample string of the audio signal, and the decoder is configured to reproduce a sample string of an audio signal in the time-domain based on the code string and the side information.

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 the previous 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 Z 1 candidates among the Z candidates for the interval T representable with the side information as the Z 2 candidates on the basis of an indicator obtainable from the audio signal and/or sample string in the current frame, where Z 2 <Z 1 .

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 Z 1 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 Z 2 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 an indicator indicating the degree of stationarity of the audio signal in the current frame is smaller than a predetermined threshold, only the Z 2 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 following conditions occurs:
(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.

9. The encoding method according to claim 1 ,
wherein the sample string encoding step comprise

Assignees

• Moriya Takehiro
• Harada Noboru
• Hiwasaki Yusuke
• Kamamoto Yutaka
• Nippon Telegraph & Telephone

Inventors

• Moriya Takehiro
• Harada Noboru
• Hiwasaki Yusuke
• Kamamoto Yutaka

Classifications

• G10L25/90

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