Keyboard CV Demystified

There seems to be a lot of misunderstanding about keyboard a.k.a. pitch CV on analog synths. You've probably heard most Moogs and ARPs are 1 Volt/Octave. I've made a video with my Moog Rogue to show what 1V/oct means.

I have the probes of my multimeter connected to the "KYBD CV OUT" and ground. First I play the low F, which puts out close to 0 V. Then I play the F an octave up (1 V) and the F two octaves up (2 V), hence 1V/oct. Note that the CV stays the same until the next note is played.

Next I play F, G#, B, D, F. What should the voltages be? If we have a 1V/oct scale and 12 notes = 1 octave, then 1V/oct = (1/12)V/note. So we get the following:

F = 0 V
G# = 3*(1/12) = 1/4 V
B = 6*(1/12) = 1/2 V
D = 9*(1/12) = 3/4 V
F = 1 V

Next I turn up the portamento. The Rogue's portamento kicks ass and I have yet to hear a softsynth duplicate it. That will be the topic of a future post. With the portamento turned up I play the lowest note and highest note to show the CV slide between the values. The high note incidentally sounded like the slow down part in "Rockafeller Skank."

Then I turn the multimeter to mV. I play the low F and F#. We would expect the voltages to be 0 mV and 83.3 mV, respectively. They are actually 2.7 mV and 85.7 mV. Why the deviation? Analog isn't perfect and that's why it's great.


Measuring Pitch CV for my Moog Rogue from Robert Hume on Vimeo.