MOTM

Even without talking about polyphony, it's still a trick to pull a pure
waveform out of an acoustic source with a comparator in order to extract the
pitch information. If you look at a single pure guitar note on a scope, you
will see that, unlike with a pure geometric synth waveform that crosses the
zero-threshold only twice per period, the acoustic wave may cross many more
times than that, and as the note continues and decays, and harmonic phases
change, the number of crossings per period may change.

Generally you want to do some gentle lowpass filtering before you get to the
comparator. You aren't using the input for sound---just for data---so you
can beat it up any way you need to in order to get that period info out of
it! So if you whack off as many of the upper harmonics as you can, THEN
square it up, you're better off.

The next issue with Pitch->CV converters is response time. The human ear can
hear some pretty low frequencies. As you start getting down there, the
amount of time it takes for a P/CV to figure out what the pitch is can be
noticeable, since typically a few cycles need to go by before the circuitry
can "lock on."

I would really love to see someone come out with a good, economical synth
module to do this. It's long been a dream of mine to own one.