[sdiy] vocoder filters

[Bernard Arthur Hutchins, Jr]

The general set of vocoder problems mentioned here yield to a specific digital approach.

First, the need for MANY (topographically similar) filters with unknown or uncertain parameters is an obvious job for programming.

Second, obviously, the equivalent of filtering can be done by taking an FFT (analysis), custom weighting the frequency domain description (the dynamics) and inverting the thusly modified FFT (synthesis).

Thirdly, since the FFT frequencies are equally spaced in Hz (requiring huge FFT sizes) the FFT is NOT well-suited to the audio/speech problem. Instead, look at the well-studied approach of MULTI-RATE DSP where lower rates at lower frequencies are used.  (It’s magic).  Things like “perfect-reconstruction filers”.  See: P.P. Vaidyanathan “Multirate Systems and Filter Banks” (Prentice-Hall, 1993) and N.J. Fliege, “Multirate Digital Signal Processing: Multirate Systems, Filter Banks, Wavelets” (Wiley 1994).

A simple introductfion: http://electronotes.netfirms.com/AN358.pdf

But first of all – What are you hoping to accomplish?


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