I have build a vocoder based on two Behringer 914 filterbanks, 14 envelope followers and two Doepfer eight channel VCAs (of which I use 14), but haven’t come round to writing about it because the circuit is quite complex. Complex in the sense that it contains quite a few modules to realize it and explaining what they all do and how they need to be interconnected is quite a task. Furthermore I want to make some music with it first so that I can include it in the write up.
After using the hardware vocoder for a while I found that the attack pot of the envelope follower did not bring much and in a next rendition of the device could best be left out. The remaining part of the enveloper follower however suits its purpose and you probably do not need the more refined Follow-O-Matic.
As you may know I created Vocode-O-Matic (D31) for Daisy Seed which has 31 filter bands and a very flexible modulation matrix / patch matrix. This version sounds soooooo much better than the hardware version, and is soooooo much more flexible in its configuration, that it is more worth my while to invest some more time in making that into a module than to write about the hardware version. But if there are any specific questions, I’m happy to answer those.