I absolutely LOVE formant/vocal/speech effects and always have. This is a module I designed based on a vocal filter schematic in Electronotes. It has a total of 4 formant filters. One of them is fixed. The other 3 have voltage controlled Q (resonance) and cutoff. The output of all 4 filters goes through a notch filter to add a nasal quality (this can be turned off by dialing the notch pot all the way to either side). The notch filter cutoff is also voltage controlled.

This module is one of my favorites. Here's a link to a sound sample:

https://soundcloud.com/mike-moretti-841687688/vewa-knob-twisting

This is v1a of the board. I've replaced all the CA3080s with LM13700s and shrunk the board considerably. The filter will work with either Eurorack +/-12V or a +/-15v system. There is a Eurorack header space on the board.

Schematics, BOM and docs are here (the voce-v2b files):

https://github.com/mikemoretti3/Synths/tree/master/electronotes/misc

If you have any questions at all please let me know.