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A BRIEF OVERVIEW OF CV AND GATE TYPES
Pitch CV
The CV (control voltage) is a voltage that tells the synth what note to play. Most synths use the 1 Volt
per Octave (V/Oct) pitch scaling system to control the pitch. This means, that each octave is 1V apart
(or 0.0833V per semitone).
For example, bottom C (MIDI note #36) often corresponds to 0 Volts. The next C will be 1V, 2V, 3V etc.
This system was used by Moog, Roland, ARP and indeed most other manufacturers
except
Yamaha
and Korg.
Some other synths, most notably those by Korg and Yamaha, use a different pitch scaling system. This
is an exponential method called Hertz per volt (Hz/V). This means that for the next octave up, the voltage
is doubled. Bottom C (note#36) will be 0.25V, the next C will be 0.5V, 1V,2V, 4V etc.
Note:
the Korg
Monopoly is an exception, using V/oct scaling.
If you use a Hz/V synth with a V/oct pitch output (or vice-versa), the synth will play out of tune but will
not cause any damage to the synth.
Gate / S-Trig
The GATE signal, sometimes called V-trig (voltage trigger), is a voltage that tells the synth when to play
the note. The GATE voltage will usually be a positive voltage when the note is on, and 0V when off.
Some other synths, like Moog, Korg, and Yamaha, use S-TRIG (short-circuit trigger) instead of GATE.
This signal performs the same function, but it is a different type of signal (electrically). To tell the note to
play, the converter will provide a short-
circuit at it’s S-TRIG output (0V), and to turn off the note the
output will be open circuit (literally like opening and closing a switch).
A point to watch for; unless you know the synth, it will not always be clear what type of CV and GATE
signals are required to play the synth. For instance, the Korg MS-20 requires an S-TRIG signal, but the
input is labelled TRIG.
For more information about the various CV and Gate systems, please visit:
http://www.kenton.co.uk/info/midi-cv-info.shtml
