[sdiy] 1V/OCT

[Tim Parkhurst]

Hi Guillaume!

Yes, you basically have it right. In a 1V/Octave synth, changing the control
voltage to the VCO by +1 volt will raise the VCO frequency 1 octave. I don't
really know if there is an established "middle frequency", although if you
wanted to cover the entire audio range you might try

0V = 20Hz
1V = 40
2V = 80
3V = 160
4V = 320
5V = 640
6V = 1280
7V = 2560
8V = 5120
9V = 10240
10V = 20480

Most VCOs use a CV range of 0 to +10 volts, and many will respond to
negative control voltages by producing even lower frequencies. Another name
for 1v/oct is "exponential response". This is the standard used by most
analog synthesizers. The other type of response is Volt/Hertz or "linear
response". This is the scheme used by some of the earlier Japanese synths
(early Korg like the MS-10 and MS-20, Roland like the 100 series). With a
linear VCO, you might get something like 5V = 500Hz, 6V = 1000Hz, 7V =
1500Hz, 8V = 2000Hz and so on. Linear response was also used in the first
Moog Taurus pedals and is still used in the PAIA Fatman. Linear VCOs are
easier to build, but they have several disadvantages - the most obvious
being that they are not transposed as easily. Think about two or three VCOs
in a system, each running at a slightly different frequency: with
exponential VCOs, you can transpose all of them up one octave by simply
adding 1 volt to the CV; with linear VCOs, each VCO will have to receive a
different CV to move it up one octave. This is not to say that linear
response systems are not useful. It's just that exponential response is much
easier to work with (from the user's point of view), especially in a modular
system.

Hope this all makes sense. Like I said, you basically have it right. 


Tim (easily transposed) Servo

"Imagination is more important than knowledge." - Albert Einstein




> -----Original Message-----
> From: Guillaume Fairfield [mailto:gfairfield at rogers.com]
> Sent: Wednesday, March 10, 2004 11:06 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] 1V/OCT
> 
> Hello all,
> 
> I'm also new to this whole synth building business and am trying to
> build my first vco. I think I have a plan but I'm unsure of to the whole
> 1V/OCT thing.
> What's the standard? Is it that +1V gives an octave higher or lower? And
> what's the middle frequency? In other words what frequency represents
> 0V? Maybe I'm missing something but that's the biggest piece of the
> puzzle left, apart from all the math.
> 
> Thank you for this list...I think I'm gonna learn alot here.
> 
> guillaume
> 
> 
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