Audio signal time-scale modification method using variable length synthesis and reduced cross-correlation computations

摘要

Disclosed is an audio signal time-scale modification which utilizes variable length synthesis for the improvement of output audio quality and reduced cross-correlation computations for the reduction of computation loads to a processor. An analysis window consisting of N+Kmax audio samples is selected from an input audio samples and is shifted by the predetermined interval along output audio samples to find optimal shift Km, which ensures best cross-correlation between Nov audio samples of the analysis window and last Nov audio samples of the output audio samples and a particular value of Nm at which a coefficient of correlation between them is larger than a reference value or is the maximum one among a plurality of coefficients of correlation calculated with varying the value of Nov. The audio samples involved in the calculation of cross-correlation are down-selected by the predetermined ratio from Nov audio samples of the analysis window and last Nov audio samples of the output audio samples, respectively. The analysis window may also be shifted by the plurality of audio samples per one shift. The audio samples ranged region (Km+Nov−Nm)^th sample in the analysis window is determined as an add frame. The existing last Nm audio samples of the output audio samples are replaced with new Nm audio samples obtained by weighting and adding the overlapped parts, i.e., the first Nm audio samples of the add frame and the last Nm audio samples of the output audio samples, while remaining part of the add frame is simply appended to the tail of the new Nm audio samples in the output audio samples.