[sdiy] Pitch-to-voltage converters

[David G. Dixon]

> It will work well for that, but it will only update every other cycle...

I know an easy way to make it update on every cycle, specifically for a saw
wave input.  Simply use a saw doubler (e.g., a one-input version of Ken
Stone's Wave Multiplier) to generate a saw at twice the frequency, and feed
that to the EFM F-V converter.  Of course, trimming the doubler to generate
exactly twice the incoming saw frequency would be critical to achieving
accuracy.  Otherwise, the output voltage would oscillate slightly at the saw
frequency.  However, the trimming could be achieved easily by watching the
F-V converter output on a scope, and simply trimming until the wiggle in the
voltage disappears.  It might also require AC-coupling the incoming saw to
ensure zero DC offset.

However, for my application, updating on every other cycle is plenty fast.
Indeed, a simple tachometer (i.e., constant-width pulse integrator) circuit
would probably be plenty fast, even at very low audio saw rates, since the
LFOs being controlled would be oscillating at well below audio rates.  I
just think that the EFM circuit is so damned elegant that I can't imagine
not using it!