[sdiy] Hard Sync on DCOs

[Richie Burnett]

> My question was basically "For the cost of one comparator, why didn't more DCO
> synths do this?" It just struck me as a bit odd, that's all.

Okay, now I understand what you're proposing.  Initially I was confused the same
as Florian because DCOs don't have an analogue reset comparator.

As Scott Nordlund said I think it comes down to CV resolution.  In a normal DCO
the CV only controls the ramping rate of the integrator.  It really doesn't need
to be that accurate at all because the pitch is fixed by the reset pulses from
the digital counter.  An error as big as 10% would only cause the peak-to-peak
amplitude to change by less than 1 dB, which is marginal for audibility.

However, if you start using this analogue CV signal to determine the pitch of a
free-running oscillation you run into a whole load of problems.  A 10% change in
the rate of this oscillation would most certainly be very audible, as would any
drift in the capacitor value due to temperature changes.

I know the ultimate "pitch" of a sync'd oscillator is determined by the syncing
master, but I still think it would produce some pretty uneven timbre changes
across the keyboard, and maybe as notes are pitch-bent too.  The idea of the DCO
was originally to get away from this dependance on high analogue accuracy and
susceptibility to drift with temperature.

-Richie,