wiki/V/Oct Tuning

The standard method of using CVs to tune oscillators (or anything else that’s tuned, like some filters) is the so-called “Volt Per Octave” or “V/Oct” system. As the name implies, a change of 1 volt equals a pitch change of 1 octave. The signal is linear with respect to musical tuning (steps, semitones, octaves) which means it’s logarithmic with respect to frequency (each octave is double going up or half going down). Zero volts is C0 (16.352 Hz).

Examples

Integer voltages are always a C. 2V corresponds to C2, 3V to C3, etc. An interval of one semitone is 1/12 of a volt, corresponding to the 12 semitones in an octave in standard diatonic tuning.

2 volts is C2. 6 semitones above C2 would be F#, and would be achieved with the following CV: 2V + (6 × 1/12V) = 2V + 0.5V = 2.5V.

5 volts is C5. Moving down a perfect fifth (7 semitones) would require a change of (7 × 1/12V) = 0.5833V. Therefore, F4 would be 5V - 0.5833V = 4.4166V (4 5/12 volts).

Starting at D3 (3.166V), moving up an octave and a major third would be 16 semitones, or (16 × 1/12V) = 1.333V. F#4 = (3.166V + 1.333V) = 4.5V.