Volatile voltages: CVs, triggers and gates
Before MIDI, some (not all) analogue synthesisers could be interconnected via the decidedly primitive means of shuttling actual voltages back and forth. This method of interconnection made use of two or three distinct signal types. Envelopes could be triggered via voltage gates (essentially a voltage that is held at a steady state for a given period of time – say for as long as a key is held down), as well as triggers (short voltage spikes). The latter might also be used to sync sequencers together.
The third signal was the control voltage. Most commonly used to control pitch, this could also be used for filter cutoff and other destinations that expected to see a continuously changing voltage.
The trouble with control voltage was that manufactures never settled on any standards. Moog’s 1-volt-per-octave signals were useless when attempting to control, say, a Korg MS-20, with its oscillators scaled to Hz-per-volts. Likewise, the gates and triggers were not always compatible between units. Worse still, synth manufacturers couldn’t be bothered to agree upon what sort of cables and connectors should be used.
Thanks to the modern modular synthesiser renaissance, control voltages are back, and along with them all of the headaches of yore. Thankfully, computer musicians have quite a few options for taking control over CV-based instruments. Plugins such as MOTU’s Volta and Expert Sleepers’ superb Silent Way allow analogue synth users to play, sequence and modulate their hardware right from within their DAWs – though doing so requires an audio interface with ‘DC-coupled’ outputs or a dedicated hardware interface module such as Expert Sleepers’ ES-3.
Recently, we’ve seen similar solutions pop up in the form of Max for Live devices and Reaktor Blocks, bridging the worlds of hardware and software modular synthesis.
These programs offer an added benefit: they can be used to ‘re-calibrate’ the scaling of cantankerous vintage oscillators, bringing notoriously unstable instruments like EMS’ Synthi A and VCS 3 lock-step into tune.