[sdiy] Filters

[Chris Crosskey]

All this talk of non-resonant filters and how to make them resonate 9ie the
RC stuff) prompts me to ask a similar question.....for reasons to do with my
lack of sense I'm thinking about trying to design a vocoder. Becasue I'm
lookgin for quite high quality vocoding I'm looking to build it around 24
channels of 36dB/Oct filters plu sa Bode hi-pass bleedthrough, and if I get
that far also ripping off the Elektor voiced/unvoiced detector circuitry (or
at lest its principles)....so what I'm looking for is a stable sensible 36dB
filter, preferably built around npn transistors (I'll be using 3046-based
VCA's so I might as well use 3046 based filters if I can) and capable of
running a fairly high signal level (to improve signal to noise) If I can
manage it I'm going to try to get 2 channels per Eurocard and mount the
whole lot in a 3U rack, which I have kicking around somewhere....Any ideas
on where to start, Horowitz and Hill weren't a lot of help in that
regard...simple fixed fitler and hwo to change the frequencies by swapping
out resistor adn cap values....

chrisc