Buchla Bongos with Ring Mod and Wave Folding
Buchla Bongos are a classic west-coast percussion sound. It’s not intended to be a realistic bongo simulation. Nor is there one specific Buchla Bongo patch, it’s more of a general technique.
The basic patch is pretty easy. It has two main components a complex oscillator, and a low-pass gate. Create an harmonically rich oscillator through audio-rate frequency/amplitude/ring modulation, and wave folding. Then pass the signal through a low-pass gate (LPG) excited by a short, percussive envelope.
For a brief introduction to LPGs see here, or read this article from Perfect Circuit.
1: Detune VCO-A and B by some inharmonic amount.
2: In the mixer, turn up the ring mod and VCO-A sine.
3: VCO B sine is normalled to VCO-A FM-2, but you can experiment with different waveforms.
4: ENV-A is normalled to VCO-A index mod. Set ENV-A to have a different decay time from ENV-B.
5: Switch the TZFM switch up. Flip the AC/DC switch up and down. Use whichever setting sounds right to you. Then set the VCO A mod and index dials to taste.
VCO-A FM2 has a VCA built in (see fig 2). FM2 goes to the VCA input, and IM (index modulation) in goes to the CV in. The index slider controls the amount of FM2 going through the VCA. The MOD slider controls the amount that IM attenuates FM2.
6: Make the FM and wave folding more dynamic by switching the ENV-A control source switch up to level/velocity.
7: Patch ENV-A to Wave Folder fold in. Patch the mixer to the Wave Folder audio in. Then raise the Wave Folder’s mod and Fold sliders.
8: Patch the wave folder to the LPF audio in.
9: Turn the VCA B/LPF switch up. This puts it into LPG mode (CV controls both amplitude and frequency).
10: Patch ENV B to LPF CV in.
Use a decay only envelope to simulate an LPG. Pull the ENV-B Rise slider all the way down.
Give it a plucky but dynamic shape. Pull the ENV B shape slider all the way down. Then, patch MIDI velocity to ENV-B shape. Only push the shape slider up just slightly, you want it to stay fairly percussive, but with a short exponential tail.
11: Patch the LPF to main 1.
12: Play with the VCO octave settings to find different sounds.
13: Add some spring reverb to complete the sound.
Further Reading
A basic Buchla bongo patch by Todd Barton.
All hail the 292t Buchla & Tiptop Audio
Stazma making some bongos with the Titptop/Buchla series modules.
An article from Perfect Circuit explaining what low pass gate are and how they work.
A short article from Noise Engineering describing low-pass gates.