AW: Re: Idea for a CV quantizer

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Thu Feb 29 19:55:00 CET 1996


> But you can simplifiy it a lot; since you'll be S/H-ing anyway you
> don't really need a stepping integrator.  Use a regular sawtooth
> integrator, a counter, a comparator, a S/H, and only allow the S/H to
> be triggered on the counter clock pulse.  Easy.

Yes, I came to something similar last night! Just two sawtooth generators,
one with approx. 100 times the frequency of the other. It is important
that the fast one is hard-synced to the slow one to eliminate a
random offset. The two generators would be identical and connected
to the same voltage reference, only one cap would be 100 times
larger than the other. So a lot of the possible drift effects should
cancel out ...
Every time when the slow sawtooth crosses the input CV, the next
reset pulse of the fast sawtooth is used to sample the CV.
Every time the slow sawtooth reaches its upper limit (beyond the
input CV range), both generators are reset by discharching the caps.

I *hope* this should be accurate enough. If we even can build VCO's that
track to each othe rover decades, it should be simple to build
fixed frequency oscillators that keep their frequency relative to each
other!
The main problem which I still see, is that any jitter of the sample pulses
would cause some voltage error, and I'm not sure if I can keep all
the propagation delays constant enough!
100kHz means 100us for a semitone, this means 100ns for one Cent.
Do you think it is achievable to keep the long-time ( 1 day) drift below
these 100ns? The staircase approach would have the advantage
of being less sensitive to this ... I'm really not sure yet what would be 
better.


JH.










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