Spectral transposition of a digital audio signal

摘要

In this spectral transposition system for digital audio signals, the coefficients in an analysis filter are passed directly to the synthesis filter so that the coefficients in both filters match. The single unit delays in either or both of the analysis and synthesis filters are replaced by all-pass filters that provide a non-integer delay or an integer delay where the integer is greater than one. Thereby the transfer function for the analysis filter and/or synthesis filter is compressed/expanded depending on the transfer function of the all-pass filters. Thus, the dominant peaks or formants in the frequency spectrum of the resynthesized audio signal is transported to a user determined frequency range. The delay may be constant or variable over frequency. If the delay is variable over frequency so that it is other than 1.0 in the portion of the spectrum of interest for transposition of the spectral envelope and returns to 1.0 at the ends of the spectrum, the spectral envelope may be compressed or expanded without replication. <IMAGE>