[sdiy] Programmable ICs / Scaling

[Oren Leavitt]

Hi Nate and All,

I take it, that you are looking for a means of translating a non-standard CV to 1V/Oct.

If you're working in the analog domain you could do something like this for the V/Hz (PAiA/Korg) CV case:

V/Hz CV input from synth -> Scale pot (adjust for linearity) -> 'anti-log' amplifier -> scale pot (adjust for 1V/Oct) and buffer -> 1V/Oct CV output

However, the resulting 1V/Oct output may not be perfectly linear as voltage-to-voltage conversion between linear and log tends to be error prone.

If the source CV is linear but not 1V/Oct, then a simple non-inverting op-amp scaling circuit will work.


In the digital domain, you'll need to account for the accuracy of the analog to digital conversion of the log V/Hz voltage - especially on the low end.


Hope that helps - maybe others might have better ideas.
Oren

-----Original Message-----
From: nN AAt     e     e <timexheater at comcast.net>
Sent: Mar 4, 2004 3:32 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Programmable ICs / Scaling

i just got to wondering how one would go about say... taking something like
a performance synth that may not be 1v/oct and doing the math to figure out
what the scale is, then make something to convert it to 1v/oct...

...while mostly using programmable ICs as to make it [slightly] easier to
deal with math problems.

i know this isnt very hard to convert old korg/paia standards to roland
using analog based converters, but what would be good ICs to check out that
should be able to handle the voltage ranges of a synth? it doesn't seem like
it would be too difficult using something like PICs or Stamps, but i havent
really worked with either of them before.

has anyone here made any custom scaling devices?

this would probably be only used for cv output [nonstandard-> 1v/oct], but
1v/oct inputs would be pretty cool later on too.

- nate