Encoder, decoder, coding method, decoding method, coding program, decoding program and recording medium

• US 10,629,214 B2
• Filed: 11/26/2018
• Issued: 04/21/2020
• Est. Priority Date: 05/01/2014
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Moriya, Takehiro, Kamamoto, Yutaka, Harada, Noboru
• Primary Examiner(s): Blankenagel, Bryan S
• Application Number:
  US16/199,387
• Publication Number:
  US 20190096414A1
• Time in Patent Office: 512 Days
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 25/90 Pitch determination of speech signals
• CPC Class Codes: H03M 7/40 Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code

Abstract

An encoder and a decoder are provided that are capable of reproducing a frequency-domain envelope sequence that provides high approximation accuracy around peaks caused by the pitch period of an audio signal by using a small amount of code. An encoder of the present invention comprises a periodic-combined-envelope generating part and a variable-length coding part. The periodic-combined-envelope generating part generates a periodic combined envelope sequence which is a frequency-domain sequence based on a spectral envelope sequence which is a frequency-domain sequence corresponding to a linear predictive coefficient code obtained from an input audio signal and on a frequency-domain period. The variable-length coding part encodes a frequency-domain sequence derived from the input audio signal. A decoder of the present invention comprises a periodic-combined-envelope generating part and a variable-length decoding part. The periodic-combined-envelope generating part generates a periodic combined envelope sequence which is a frequency-domain sequence based on a spectral envelope sequence which is a frequency-domain sequence corresponding to a linear predictive coefficient code and on a frequency-domain period. The variable-length decoding part decodes a variable-length code to obtain a frequency-domain sequence.

Claims

1. A decoder comprising:

circuitry configured to;

execute an indicator decoding processing in which the circuitry decodes an inputted indicator code to obtain an indicator of a degree of periodicity; and

when the indicator is within a predetermined range indicating high periodicity, execute a periodic-combined-envelope generating processing in which the circuitry generates a periodic combined envelope sequence, W_M[1], . . . , W_M[N], which is a frequency-domain sequence by changing values of samples of a spectral envelope sequence, W[1], . . . , W[N], which is a frequency-domain sequence corresponding to an inputted linear predictive coefficient code based on a frequency-domain period corresponding to an inputted period code, the inputted linear predictive coefficient code being received from an encoder and obtained from an input time-domain audio signal at the encoder, wherein values of samples of the spectral envelope sequence are changed as in the following formula;

W_M[n]=W[n]·

(1+δ

·

P[n]),

wherein P[n] is a periodic envelope sequence P[1], . . . , P[N], and δ

is a predetermined value or a chosen value from candidates;

wherein when the indicator is within the range indicating high periodicity, execute a variable-length-coding-parameter calculating processing in which the circuitry calculates a variable-length coding parameter dependent on an amplitude value from the periodic combined envelope sequence; and

when the indicator is not within the range indicating high periodicity, execute a second variable-length-coding-parameter calculating processing in which the circuitry calculates a variable-length coding parameter dependent on an amplitude value from the spectral envelope sequence; and

execute a variable-length decoding processing in which the circuitry uses the variable-length coding parameter to perform decoding an inputted variable-length code.

5. A non-transitory computer-readable recording medium on which the decoding program for causing a computer to function as the decoder according to claim 1 or 2 is recorded.

2. A decoder comprising:

circuitry configured to;

when an inputted indicator of a degree of periodicity is within a predetermined range indicating high periodicity, execute a periodic-combined-envelope generating processing in which the circuitry generates a periodic combined envelope sequence, W_M[1], . . . , W_M[N], which is a frequency-domain sequence by changing values of samples of a spectral envelope sequence, W[1], . . . , W[N], which is a frequency-domain sequence corresponding to an inputted linear predictive coefficient code based on a frequency-domain period corresponding to an inputted period code, the inputted linear predictive coefficient code being received from an encoder and obtained from an input time-domain audio signal at the encoder, wherein values of samples of the spectral envelope sequence are changed as in the following formula;

W_M[n]=W[n]·

(1+δ

·

P[n]),

wherein P[n] is a periodic envelope sequence P[1], . . . , P[N], and δ

is a predetermined value or a chosen value from candidates; and

when the indicator is within the range indicating high periodicity, execute a variable-length decoding processing in which the circuitry decodes an inputted variable-length code to obtain a frequency-domain sequence, on the assumption that the amplitude value of the frequency-domain sequence is greater for a frequency with a greater value of the periodic combined envelope sequence; and

when the indicator is not within the range indicating high periodicity, execute a variable-length decoding processing in which the circuitry decodes an inputted variable-length code to obtain a frequency-domain sequence, on the assumption that the amplitude value of the frequency-domain sequence is greater for a frequency with a greater value of the spectral envelope sequence.

3. A decoding method executing:

decoding an inputted indicator code to obtain an indicator of a degree of periodicity; and

determining that the indicator is within a predetermined range indicating high periodicity, generating a periodic combined envelope sequence, W_M[1], W_M[N], which is a frequency-domain sequence by changing values of samples of a spectral envelope sequence, W[1], W[N], which is a frequency-domain sequence corresponding to an inputted linear predictive coefficient code based on a frequency-domain period corresponding to an inputted period code, the inputted linear predictive coefficient code being received from an encoder and obtained from an input time-domain audio signal at the encoder, wherein values of samples of the spectral envelope sequence are changed as in the following formula;

W_M[n]=W[n]·

(1+δ

·

P[n])

wherein P[n] is a periodic envelope sequence P[1], P[N], and δ

is a predetermined value or a chosen value from candidates;

calculating a variable-length coding parameter dependent on an amplitude value from the periodic combined envelope sequence; and

using the variable-length coding parameter to perform decoding an inputted variable-length code.

4. A decoding method executing:

determining that an inputted indicator of a degree of periodicity is within a predetermined range indicating high periodicity, generating a periodic combined envelope sequence, W_M[1], . . . , W_M[N], which is a frequency-domain sequence by changing values of samples of a spectral envelope sequence, W[1], W[N], which is a frequency-domain sequence corresponding to an inputted linear predictive coefficient code based on a frequency-domain period corresponding to an inputted period code, the inputted linear predictive coefficient code being received from an encoder and obtained from an input time-domain audio signal at the encoder, wherein values of samples of the spectral envelope sequence are changed as in the following formula;

W_M[n]=W[n]·

(1+δ

·

P[n]),

wherein P[n] is a periodic envelope sequence P[1], . . . , P[N], and δ

is a predetermined value or a chosen value from candidates; and

decoding an inputted variable-length code to obtain a frequency-domain sequence, on the assumption that the amplitude value of the frequency-domain sequence is greater for a frequency with a greater value of the periodic combined envelope sequence.