From dfevans@barrow.uwaterloo.caWed Nov 29 10:30:23 1995 Date: Wed, 29 Nov 1995 12:37:58 -0500 (EST) From: David Evans To: "Pierre Z." Cc: Nthings@aol.com, analogue@hyperreal.com Subject: Re: CV gate? Pierre Z. wrote: > > On Wed, 29 Nov 1995 Nthings@aol.com wrote: > > > alot of people are always talking about a CV gate what is it? > > > It's kinda like MIDI. It is what was used before MIDI in most synthesizers. > Each manufacturer had their own version of it, so not all CV/gates are > compatible. > In more detail... Many analogue synthesizers have components which are controlled by an input voltage. For example, an oscillator's pitch would be proportional to a voltage applied to some control point (hence VCO--Voltage Controller Oscillator.) Some synths bring these control points out to the panel, so you can control the pitch of the VCO from some external source. This can apply to other parts of the synthesizer; filter cutoff, pulse width, mixing levels, etc. All of these are Control Voltages--hence CV. The "Gate" is typically used to control the envelopes. An envelope may fire when a voltage is applied, go through its attack/decay/sustain cycles, and then go through the release cycle when the voltage goes away. So, by using a CV driving a VCO and a gate signal, you can play one synth from something capable of producing these CV and Gate signals. This could be another synth (with the CV and gate derived from the keyboard), a sequencer, a plastic bag--you name it. As far as VCO pitch goes (and VCF cutoff too), many manufactures followed the "1V/Oct" standard, meaning that a change in CV of 1V would cause the pitch to change by 1 octave. This is nice, because the voltage is proportional to the note played. If you offset the input voltage with some value (ie. add a constant voltage) then all notes are transposed equally. Some companies used things like 0.9V/Oct, or 1.2V/Oct, but the idea is the same. The other "standard" makes voltage change proportional to *frequency*, not note. Each time you go up an octave, the frequency doubles. So, with the 1V/Oct system, of you plotted a graph of input voltage vs. note, you would get a straight line. However, if you plotted a graph of input voltage vs. *frequency*, you would get an exponential. With a "V/Hz" system, plotting voltage vs. frequency gives you a straight line. You can likely imagine then that plotting voltage vs. note gives you a logarithmic graph. -- David Evans (NeXTMail OK) dfevans@bbcr.uwaterloo.ca Computer/Synth Junkie http://bbcr.uwaterloo.ca/~dfevans/ University of Waterloo "Default is the value selected by the composer Ontario, Canada overridden by your command." - Roland TR-707 Manual