A modular synth carries audio, control voltage, and gate/trigger signals on identical jacks, and the distinction is convention not physics

A modular synth routes functionally distinct kinds of signal through identical jacks. Three core kinds recur across formats: audio — the raw sonic material from oscillators and noise, an AC signal in the ~20 Hz–20 kHz band (roughly ±5 V / 10 Vpp); control voltage (CV) — a DC voltage from modulation sources (LFOs ~±2.5 V, envelopes 0 to +8 V) that sets parameters like pitch, cutoff, or amplitude; and trigger/gate/clock — rectangular pulses (0/+5 V, sometimes +12 V) that start events on their fast rising edge. Only rectangle-shaped waveforms suit triggers/gates, because a slowly-sloping sine, triangle, or sawtooth lacks the fast edge a module needs to fire reliably. Gate and trigger differ in duration: a gate stays high while a note is held (‘note on/note off’, sustaining an ADSR), whereas a trigger is a momentary pulse (a clock tick or drum hit — a gate with zero sustain). Crucially these categories are conventions, not physical rules; the same cable carries any of them, and an audio-rate signal fed into a CV input becomes FM. That deliberate porousness is the source of modular’s flexibility.

Examples

One LFO shows all three roles: its square output into a clock divider acts as a clock; its triangle output into a VCF cutoff acts as CV (filter wobble); the same LFO at audio rate into a mixer acts as audio, or into a VCO’s FM input becomes vibrato/FM. A sequencer GATE into an ADSR gate input sets note length; a clock TRIG into a drum module fires a hit.

Assessment

Name the three core signal kinds with their typical voltage ranges, and explain the difference between a gate and a trigger. Diagnose: a friend patches a slow sine LFO into a gate input and the ADSR fires erratically — why? Give one example of deliberately using a signal outside its ‘intended’ category and the sonic result.