My $0.02....
If we assume that the quality of a Vocoder is measured by its
intelligibility, then I can think of three main factors which are
important in the design:
1. Bandpass filter rolloff slopes (the steeper the better)
2. Number of bandpass filters (the more the better)
3. Analyzer envelope follower lag (the less the better)
Since you're starting with a hi-fi graphic EQ, we can see that 1 and 2
are not going to be real optimal, so you're right that there's no real
need for high-quality envelope followers.
I'd suggest trying a simple one-diode peak detector, with a resistor
bleeder, followed by a buffer. Although a truly well-designed envelope
follower needs to respond properly over a wide frequency range, you
can probably get away with such a simple solution because you can
tweak the R/C values for each band differently.
- Gene
gstopp at fibermux.com
______________________________ Reply Separator _________________________________
Subject: Envelope followers for vocoder.
Author: midas at teleport.com (Brian Coates) at ccrelayout
Date: 2/22/97 9:57 AM
I need to find a schematic for a cheapy envelope follower. I found a 10
band graphic EQ yesterday for 5 bucks, and I want to use the stereo
channels separately for a vocoder. I'll use the left channel filters for
the instrument input, and the right channel for the microphone input. I
need to put VCA's on the outs of the left channel filters, which I have
schematics for several, but I need a simple follower for the outputs of the
right channel filters to drive the VCAs
This should only take a couple of afternoons, and I probably have all the
parts already. So hopefully, I'll walk away from this with a $5 vocoder.
I also found a five band eq for $4 that I picked up. I figure no, it won't
be easy to understand words, but nonetheless, make some interesting sounds.