Encoding apparatus, decoding apparatus, and method and program for the same
There are provided an encoding or decoding technique capable of performing more efficient encoding or decoding than before. An encoding apparatus for encoding a time-series signal in a frequency domain is provided with: a spectral envelope estimating portion 2 A estimating a spectral envelope, regarding absolute values of a frequency domain sample sequence corresponding to the time-series signal raised to the power of η as a power spectrum, on the assumption that η is a predetermined positive number other than 2; and an encoding portion 2 B performing such encoding that changes bit allocation or that bit allocation substantially changes, for each coefficient of the frequency domain sample sequence corresponding to the time-series signal, based on the estimated spectral envelope.
1. An encoding apparatus for encoding a time-series signal in a frequency domain, the encoding apparatus comprising:
a spectral envelope estimating portion estimating a spectral envelope, regarding absolute values of a frequency domain sample sequence corresponding to the time-series signal raised to the power of as a power spectrum, on the assumption that η is a predetermined positive number other than 2; and
an encoding portion performing such encoding that changes bit allocation or that bit allocation substantially changes, for each coefficient of the frequency domain sample sequence corresponding to the time-series signal, based on the estimated spectral envelope.
2. The encoding apparatus according to claim 1 , wherein
the spectral envelope estimating portion comprises a linear prediction analyzing portion performing linear prediction analysis using a pseudo correlation function signal sequence obtained by performing inverse Fourier transform regarding the absolute values of the frequency domain sample sequence raised to the power of η as the power spectrum to obtain coefficients transformable to linear prediction coefficients, and an unsmoothed spectral envelope sequence generating portion performing estimation of the spectral envelope by obtaining an unsmoothed spectral envelope sequence which is a sequence obtained by raising a sequence of an amplitude spectral envelope corresponding to the coefficients transformable to the linear prediction coefficients to 1/η.
3. A decoding apparatus for obtaining a frequency domain sample sequence corresponding to a time-series signal by decoding in a frequency domain, the decoding apparatus comprising:
a linear prediction coefficient decoding portion decoding inputted linear prediction coefficient codes to obtain coefficients transformable linear prediction coefficients;
an unsmoothed spectral envelope sequence generating portion obtaining an unsmoothed spectral envelope sequence which is a sequence obtained by raising a sequence of an amplitude spectral envelope corresponding to the coefficients transformable to the linear prediction coefficients to the power of 1/η, on the assumption that η is a predetermined positive number other than 2; and
a decoding portion obtaining a frequency domain sample sequence corresponding to the time-series signal by decoding inputted integer signal codes in accordance with such bit allocation that changes or substantially changes based on the unsmoothed spectral envelope sequence.
4. An encoding method for encoding a time-series signal in a frequency domain, the encoding method comprising:
a spectral envelope estimating step of estimating a spectral envelope, regarding absolute values of a frequency domain sample sequence corresponding to the time-series signal raised to the power of η as a power spectrum, on the assumption that η is a predetermined positive number other than 2; and
an encoding step of performing such encoding that changes bit allocation or that bit allocation substantially changes, for each coefficient of the frequency domain sample sequence corresponding to the time-series signal, based on the estimated spectral envelope.
5. The encoding method according to claim 4 , wherein
the spectral envelope estimating step comprises a linear prediction analyzing step of performing linear prediction analysis using a pseudo correlation function signal sequence obtained by performing inverse Fourier transform regarding the absolute values of the frequency domain sample sequence raised to the power of η as the power spectrum to obtain coefficients transformable to linear prediction coefficients, and an unsmoothed spectral envelope sequence generation step of performing estimation of the spectral envelope by obtaining an unsmoothed spectral envelope sequence which is a sequence obtained by raising a sequence of an amplitude spectral envelope corresponding to the coefficients transformable to the linear prediction coefficients to 1/η.
6. A decoding method for obtaining a frequency domain sample sequence corresponding to a time-series signal by decoding in a frequency domain, the decoding method comprising:
a linear prediction coefficient decoding step of decoding inputted linear prediction coefficient codes to obtain coefficients transformable linear prediction coefficients;
an unsmoothed spectral envelope sequence generating step of obtaining an unsmoothed spectral envelope sequence which is a sequence obtained by raising a sequence of an amplitude spectral envelope corresponding to the coefficients transformable to the linear prediction coefficients to the power of 1/η, on the assumption that η is a predetermined positive number other than 2; and
a decoding step of obtaining a frequency domain sample sequence corresponding to the time-series signal by decoding inputted integer signal codes in accordance with such bit allocation that changes or substantially changes based on the unsmoothed spectral envelope sequence.
7. A non-transitory recording medium which stores therein a program for causing a computer to function as each portion of the encoding apparatus according to any of claims 1 and 2 or the decoding apparatus according to claim 3 .