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I've always been a bit hazy on Wendy Carlos's A Clockwork Orange era vocoder. There seems to be a general consensus that she either modded some Moog modules, or got Bob Moog to mod them for her, but information's scarce.
Thankfully, Wendy Carlos shows and explains her setup on her own website: http://www.wendycarlos.com/photos.html
This was Wendy Carlos's Moog modular as it looked in 1977. Here I've highlighted the modules she vocoded with. I'm not sure if she modded them herself or badgered Bob Moog into doing it for her, but the fixed filter banks have been customised.
The 907 fixed filter bank, top-left, has an output for each of the ten bands. These are then fed into ten pairs of envelope followers (to track each band's volume) and VCAs (to make a signal louder or quieter to match that band).
These then appear to feed into the 914 fixed filter bank (like the 907 but with four more bands, presumably ignored), presumably overriding or adding to each band's volume knob positions.
I wonder if instead you could simply have two fixed filter banks modded in the exact same way, with independent outputs, and feed the second one's outputs into the VCAs' audio inputs? I *think* that might work, but obviously haven't tried it.
Matching fixed filter banks, either two 907s or two 914s, would probably have been preferable. I'd imagine the 914's highpass and lowpass filters would make room for the extra (unused here) four bands, causing a bit of a notch near the top and bottom.
Anyway, if you see a photo of Wendy Carlos at her synth, and there's thick groups of cables tied together near the top, that's her jerry-rigged vocoder. Neat!
