Periodic-combined-envelope-sequence generation device, periodic-combined-envelope-sequence generation method, periodic-combined-envelope-sequence generation program and recording medium
An envelope sequence is provided that can improve approximation accuracy near peaks caused by the pitch period of an audio signal. A periodic-combined-envelope-sequence generation device according to the present invention takes, as an input audio signal, a time-domain audio digital signal in each frame, which is a predetermined time segment, and generates a periodic combined envelope sequence as an envelope sequence. The periodic-combined-envelope-sequence generation device according to the present invention comprises at least a spectral-envelope-sequence calculating part and a periodic-combined-envelope generating part. The spectral-envelope-sequence calculating part calculates a spectral envelope sequence of the input audio signal on the basis of time-domain linear prediction of the input audio signal. The periodic-combined-envelope generating part transforms an amplitude spectral envelope sequence to a periodic combined envelope sequence on the basis of a periodic component of the input audio signal in the frequency domain.
1 . A periodic-combined-envelope-sequence generation device comprising:
processing circuitry configured to:
execute a spectral-envelope-sequence calculating processing which takes, as an input audio signal, a time-domain audio digital signal in each frame which is a predetermined time segment, and calculates a spectral envelope sequence of the input audio signal on the basis of time-domain linear prediction of the input audio signal; and
execute a periodic-combined-envelope generating processing which transforms the spectral envelope sequence to a periodic combined envelope sequence on the basis of a periodic component of the input audio signal in the frequency domain;
wherein the periodic-combined-envelope generating part modifies the periodic combined envelope sequence based on a value that determines a mixture ratio between the spectral envelope sequence and the periodic component; and
the value that determines the mixture ratio is chosen such that the shape of the periodic combined envelope sequence and the shape of absolute values of a coefficient string which is transformed from the input audio signal in the frequency domain becomes similar to one another.
2 . A non-transitory computer-readable recording medium on which the periodic-combined-envelope-sequence generation program for causing a computer to function as the periodic-combined-envelope-sequence generation device according to claim 1 is recorded.
3 . A periodic-combined-envelope-sequence generation method, executing:
a spectral-envelope-sequence calculating for taking, as an input audio signal, a time-domain audio digital signal in each frame which is a predetermined time segment, and calculating a spectral envelope sequence of the input audio signal on the basis of time-domain linear prediction of the input audio signal; and
a periodic-combined-envelope generating for transforming the spectral envelope sequence to a periodic combined envelope sequence on the basis of a periodic component of the input audio signal in the frequency domain;
wherein the periodic-combined-envelope generating modifies the periodic combined envelope sequence based on a value that determines a mixture ratio between the spectral envelope sequence and the periodic component; and
the value that determines the mixture ratio is chosen such that the shape of the periodic combined envelope sequence and the shape of absolute values of a coefficient string which is transformed from the input audio signal in the frequency domain becomes similar to one another.