[sdiy] Tuning indicator

[jhaible]

> How would that work for high frequencies? The counter
> would clock at the beat frequency produced by the two
> input freqs, and if the beats got faster than 40Hz
> (eye resolution) * 10 (# leds) then it would be
> unreadable. So when tuning a VCO at the high end, I
> fear this would fall short. Though the 'too high' and
> 'too low' indicators would fix this...

The counter divides the beat frequency down. Skipping
speed from one LED to the next happens with the direct
beat rate, but wandering around the whole circle means
a divided-down beat rate.

The Korg ES-50 Lambda uses a single LED to indicate beating
between two master VCOs (which control a TOS each; and
actually there are 3 VCOs and 2 LEDs). They have some flipflops
to divide the beat frequency into a pleasant range.

JH.