How to convert period CV to pitch CV

[Mark Smart]

I need to ask some advice about a project I'm planning to do at some point.
(When I'll have time, I don't know!)

I've wanted for a long time to take my Roland GR-300 guitar synth and
modify it to make it programable and more flexible in terms of sound
variety. As it is, it can only generate sawtooth waves, and all six (or
twelve) oscillators get run through a single VCF at the end. One thing I
would do to it is add a separate VCF for each pair of voices which would
track the pitch of the string from which those voices are being played.

Herein lies the problem: the GR-300's voltage-controlled oscillators do not
respond to a 1 V/octave CV, or even a CV proportional to frequency, they
are driven by a circuit which generates a CV proportional to the PERIOD of
the guitar string. Each string is set up to put out a CV of 10 volts when
the string is played open and 5 volts when the string is played at the 12th
fret.

Basically what I'm wondering is if it is possible to convert this CV to a 1
V/octave CV using analog circuitry so it can drive a Moog-style filter.

What is needed is a circuit to perform a 1/x function on the CV (this is
the part I don't know how to do) and then a linear/exponential converter to
make it 1 V/octave.

Any suggestions on the 1/x part?



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*     Mark Smart                               *
*     Network Technician                       *
*     University Communications Inc. (UCI)     *
*     smart at medusa.nn.com                      *
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