(extract from Oberkorn manual)
CVs and Gates – What are They?
This is not a complete beginner’s guide to analogue synthesizers, but here is a very brief explanation.
A CV (control voltage) is a varying voltage that can be used to control a parameter of an analogue synth. Which parameter really depends on the synth. Most synth’s have at least a pitch CV input (usually just called CV), and a filter cut-off CV input. These I think are the two most important. But a good modular will provide CV inputs to control most parameters.
Gate (sometimes called trigger) is typically used to trigger an envelope generator (which controls the synth’s volume, filter cut-off, and other parameters). Gate can be used to turn digital switches on and off, or to clock other analogue sequencers.
The beauty of analogue synth’s and modulars is that there are no rules. So you can use the CV and Gates how you want. If your synth has a voltage control input socket, then you can use it. That’s not to say any patch will sound good. Some won’t sound good or even work at all. So in those cases you’ll need to try something else. That’s the nature of modular synths.
Though you will hear terms like CV, Gate, V/Oct, Hz/V, Trigger, S-Trig, and they will have their own general characteristics, there is no true analogue standard.
V/Oct and Hz/V is about the nearest and they usually work as designed, but there are always occasional incompatibilities or exceptions.
Gates and triggers can be of different voltages and pulse widths. There is no account of input and output impedances, frequency ranges etc. Some gate outputs might be say 5v or 10v. Some synth may require a gate voltage higher than the controlling device is giving.
So though with modulars and analogues synths you should be able to cross patch with no problems sometimes things you might try may just not work. This sort of situation may happen too when you connect a sequencer to a particular synth, or try clocking two devices together. Sometimes it won’t work. Generally this is rare and whatever you hook up will usually work. There is usually a work around if there are problems, or you simply just have to try something else.
Oberkorn seems to work fine with most gear, and I have not heard back many problems.
There are two main ‘standards’ (and I use this term loosely) for pitch CV.
V/Oct means Volts Per Octave. This means that a VCO’s pitch will go up one octave for each volt added to the CV input. 0V (say) would be C, so 1V would be C one octave higher.
This is typically used by;
(old synth’s) Roland, Moog, ARP, SCI
(new synth’s) just about everyone – Analogue Solutions, Analogue Systems, Doepfer, etc.
Hz/V means Hertz Per Volt. This means that to go up one octave you must double the voltage. So (say) C is 3V, then to go up one octave the CV must be 6V.
This was typically used by the old Korg synth’s (like the MS series), though if I remember rightly, the monopoly was an exception.
Hz/V is not so flexible as V/Oct. The problems arise when trying to mix Hz/V signals to change pitch.
Oberkorn outputs a varying voltage on the CV outputs. I am often asked whether its output is V/Oct, or Hz/V. This question does not really make any sense as such. Oberkorn simple puts out the voltage that you set on the control. But for pitch control it will ‘feel’ better using V/Oct synths, which the majority of synths use.
Hz/V and V/Oct only applies to the pitch control of oscillators. For controlling parameters such as filter cut-off V/Oct or Hz/V does not apply. These ‘standards’ only apply to pitch control. Parameters such as cut-off just want a varying linear voltage. Once again there is no standard, but typical ranges are 0-5v, 0-12v, and sometimes bipolar like -12 to +12V.
The range Oberkorn puts out is usually fine for most synth’s.
The Oberkorn puts out a positive gate signal. Gate off is 0V, Gate on is 10V. Oberkorn’s gate signal is strong enough to trigger just about all analogue synth’s, envelopes, and strong enough to clock most other analogue sequencers.
There is a complication (isn’t there always?!).
Old Moog and Korg synths typically used a type of Gate called S-Trig. Though I won’t go into full details, let’s just say that it is a sort of inverted gate signal. Not inverted in polarity, but in state.
So normally a gate might be 0v for off, and, say, 5v for on.
With S-Trig it is swapped. So, say, 5v for off and 0v for on. (Though in practice S-trig is implemented in a few different ways by different synth’s).
I have not tested Oberkorn with many S-Trig synth’s (since it was designed for the ‘standard’, more common positive gate synth’s and because S-trig synth’s are typically rarer to find). But I have had reports back that it works fine with Korg MS synth’s, but inverted (as you would expect). So to trigger the synth you must set a gate switch to off rather than on!