In 1V/octave pitch control, each additional volt raises oscillator pitch by exactly one octave
The 1 volt-per-octave (1V/oct) standard, pioneered by Bob Moog and near-universal in Eurorack and most analogue modular formats, encodes pitch as control voltage: a 1 V increase doubles the oscillator’s frequency — one octave up. Because an octave has twelve semitones, one semitone is 1/12 V (≈83 mV). The mapping is linear-in-pitch but exponential-in-frequency: equal voltage steps give equal musical intervals regardless of absolute frequency, so voltages cannot be summed expecting equal Hz shifts. A 10 V range therefore spans ~10 octaves. CV is relative, not absolute: the resulting pitch is the sum of all inputs (master tune, octave switch, CV inputs), and only inputs labelled 1V/oct use this scaling — linear-FM and attenuated inputs do not. A sudden CV change makes pitch jump; a smooth change produces portamento (glide). The shared standard is what lets any keyboard, sequencer, or MIDI-to-CV converter drive any compliant oscillator across makers. Incompatible schemes exist and need conversion: Buchla uses 1.2V/oct, and vintage Korg/Yamaha synths use Hz/volt (linear-in-frequency), which produces unequal intervals for equal voltage steps.
Examples
A MIDI/CV interface outputs 0 V for C0, 1 V for C1, 2 V for C2 — patched into a 1V/oct VCO it tracks the keyboard. A VCO at A4 (440 Hz) at 0 V outputs A5 (880 Hz) at +1 V and A3 (220 Hz) at −1 V; a 0.083 V step raises one semitone. In VCV Rack, patch MIDI-to-CV’s V/oct output into a VCO’s V/oct input. A slew limiter between a keyboard’s CV out and a VCO’s CV in turns stepwise notes into glides. Korg MS-20 Hz/volt: +1 V from 0 Hz is only a 1 Hz offset — not musical.
Assessment
If a VCO plays C3 at 0 V, what CV plays C5, and what voltage equals a semitone? Show the reasoning. Explain why two 1V/oct devices from different makers patch together directly, and why a Buchla 1.2V/oct oscillator or a Hz/volt synth drifts out of tune across the range of a 1V/oct keyboard even when matched at one note.