Non CPU autotune (was AW: RE: ASM-1 Poly Controller)

[Kevin Lightner]

I have a design for a hardware autotune circuit. It basically emulates the
standard auto software routine found in many synths like OB-x's.

Basically, it uses two timers or counters (first turning off all external
modulation sources). One counter is advanced by a very fast clock, the
other by the vco that is under the test. When the vco's counter reaches 8,
it stops the first timer. The binary result of that counter is indexed into
a rom and the output of the rom is sent to a DAC which is sampled and held
and applied back to the vco CV. The table has to be configured and there is
no provision for scaling, only offset right now. I have a diagram if anyone
would like to see it. It's only a schelogic at the moment.

Any time a note is not being played, the circuit could cycle through the
vco's. If a note was to play, and the circuit was interrupted, then the vco
would either get the old CV offset or the newly sampled one, but no
undetermined value.

-Kevin