[sdiy] Hard Sync on DCOs

[Andrew Simper]

I agree with Tom, I think it would be a very cool feature, but I can
also undertand why manufacturers didn't use it. On the front panel it
would need at least one knob a clicked "off" position at the bottom,
and then increase in pitch of the vco above that. This is what I do in
a synth I did called Strobe, there is a single "sync" knob. Also
typical sync sounds need need modulation of the VCO pitch from lfo or
env, so that would be more front panel real estate gone. The 10%
tracking problem I don't think is a big deal since the main audible
pitch is still coming from the master reset clock of the sync, the 10%
would just be a change in timbre between each voice, which would sound
cool. Since there would be no way to increase the pitch of the VCO
without sync then it shouldn't matter too much.

Andy
--
cytomic - sound music software




On 10 November 2011 02:06, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>> 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,
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