Encoder, decoder, coding method, decoding method, coding program, decoding program and recording medium
View Patent ↗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.
1. An encoder comprising:
circuitry configured to:
when an indicator of a degree of periodicity of an input time-domain audio signal 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 a linear predictive coefficient code obtained from the input time-domain audio signal in a predetermined time segment based on a frequency-domain period corresponding to a period code obtained from the input time-domain audio signal, 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;
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 circuitry calculates a variable-length coding parameter dependent on an amplitude value from the spectral envelope sequence; and
execute a variable-length coding processing in which the circuitry uses the variable-length coding parameter to encode a frequency-domain sequence derived from the input time-domain audio signal by variable-length coding dependent on the amplitude value and to output a variable-length code to a decoder.
2. An encoder comprising:
circuitry configured to:
when an indicator of a degree of periodicity of an input time-domain audio signal 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 a linear predictive coefficient code obtained from the input time-domain audio signal in a predetermined time segment based on a frequency-domain period corresponding to a period code obtained from the input time-domain audio signal, 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 coding processing in which the circuitry encodes a frequency-domain sequence derived from the input time-domain audio signal 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 outputs a variable-length code to a decoder, and
when the indicator is not within the range indicating high periodicity, execute a variable-length coding processing in which the circuitry encodes a frequency-domain sequence derived from the input time-domain audio signal 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 and outputs a variable-length code to a decoder.
3. A coding method executing:
determining that an indicator of a degree of periodicity of an input time-domain audio signal 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 a linear predictive coefficient code obtained from the input time-domain audio signal in a predetermined time segment based on a frequency-domain period corresponding to a period code obtained from the input time-domain audio signal, 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 encode a frequency-domain sequence derived from the input time-domain audio signal by variable-length coding dependent on the amplitude value and to output a variable-length code to a decoder.
4. A coding method executing:
determining that an indicator of a degree of periodicity of an input time-domain audio signal 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 a linear predictive coefficient code obtained from the input time-domain audio signal in a predetermined time segment based on a frequency-domain period corresponding to a period code obtained from the input time-domain audio signal, 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
encoding a frequency-domain sequence derived from the input time-domain audio signal 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 outputting a variable-length code to a decoder.
5. A non-transitory computer-readable recording medium on which the coding program for causing a computer to function as the encoder according to claim 1 or 2 is recorded.