Synth Education

Cross-Modulation & Generative Patches

When function generators modulate each other's timing, the result is emergent complexity, patterns that nobody designed but that sound intentional. This is the capstone of West Coast synthesis.

One-Way Modulation

Start simple. FG-A cycles at 2 Hz and its output controls FG-B's fall time. Now B's decay gets shorter and longer as A cycles. Listen to the rhythm change. It's not a fixed pattern anymore; it's breathing.

Mutual Modulation

Now patch B's output back to A's rise time. Each function generator is changing the other. When A modulates B which modulates A, you have a feedback loop. At low depths, the feedback adds subtle variation, like a drummer whose timing drifts slightly with each hit. At high depths, the feedback can become chaotic: timing values swing wildly as each generator destabilizes the other. The pattern evolves on its own. Neither generator is playing the same shape it was a moment ago. You didn't program this pattern. It emerged.

Designing Systems, Not Sounds

This is generative synthesis in its simplest form. Two knobs (the cross-modulation depths) control infinite variation. Low depth: subtle, natural-sounding variation. High depth: full chaos. You're not programming a sound; you're designing a system that plays itself. This is the philosophy Don Buchla pioneered in the 1960s, and it's still the most exciting frontier in electronic music.

The Make Noise MATHS module, one of the most popular modules in modular synthesis, is essentially the two function generators and cross-modulation we have been building toward. The "Maths Patch" preset below recreates one of its signature self-playing patches.

The West Coast Journey

Over the last 12 lessons, you have moved from wavefolding (Part 64) through lowpass gates, function generators, control signals, tuning, audio-rate modulation, patching, envelopes, sequencing, and now generative patches. You have built a complete West Coast synthesizer from first principles, not by memorizing modules, but by understanding how a handful of simple ideas combine into something far greater than the sum of their parts.

References

• Make Noise: MATHS, the quintessential cross-modulation module
• MATHS illustrated supplement, classic self-playing patches
• Wikipedia: Generative Music
• Wikipedia: Don Buchla