How to convert period CV to pitch CV

[Mark Smart]

> > sawtooth wave right before it gets reset. The output of this sample and hold is the control voltage which is proprtional to the guitar string's frequency!!
> >  Pretty cool! 
> It seems that the output voltage is proportional to the string's period, right?

You're right! I knew that, I just didn't type it. Sorry.

> 
> Now, what you need is to compute 1/T to obtain a frequency-proportional voltage.
> The processing steps are:
> log() -> negate() -> exp()
> 
> The explanation is: 1/T = exp(log(1/T)) = exp(-log(T))
> 
> An interesting circuit is (pseudo-SPICE notation):
> vT 10 0 INPUT_VOLTAGE
> r1 10 12
> op-amp 12 0 14    (inverting, non-inverting, output)
> q1 12 0 14 npn    (collector base emitter)
> 
> vtranspose 20 0    (see explanation)
> q2 22 14 20 npn
> op-amp 22 0 24    (inverting, non-inverting, output)
> r2 22 24
> 
> The output voltage is at node 24.
> The circuit has 1st order thermal compensation.
> vtranspose is a NEGATIVE voltage between -0.2V and -1.0V and allows to
> transpose (tune) the output voltage.
> I didn't calculate the values of the resistors.
> 

Wow, thanks! I haven't used spice for about eight years, but I think I can
see what's going on as far as connections go.

> Very interesting. Can you draw a schematic diagram of that part?

It's a pretty complicated circuit. I have the GR300 service manual which I
got directly from Roland (you can still get these, they're about $20), and
even it is a copy. I would be willing to copy mine for people, if they
want, but it might be hard to read.

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