Fast VCOs/V->F converters

[Douglas R. Kraul]

>If I want *no* chorusing, I use a DCO, or I sync the VCOs.
>IMO, 90% of building a good pair of VCOs is getting the "right"
>beat rate over the whole range. I agree that 29Hz is too much;
>and I'd go further and say there are applications where the fun
>just starts *below* "1.837"  (but not zero !) Hz.
>

My point is one of predictable control.  Once you have that you can then
detune for *any* desired beat frequency.
I agree, verrry slow beats are very cool.  Also, I particularly don't like
the lack of warmth in any type of locked oscillator - too mechanical
sounding, unless that is what I am after.  But I do very much want to set
things up as I want them, not as the circuit decides them to be, especially
if it varies when I don't want it to.

>I share your doubts about PLLs, for the reason Martin and others
>mentioned earlier: No clean transition between notes. But I don't
>understand "never quite getting there" - once it's locked, it's locked
>in *phase*, which implies being locked in frequency, too. (In theory,
>you might have an infinite response on pitch changes in the PLL, but
>in reality it will be really locked after some time.)
>

Not true.  There is always a small amount of phase noise in the loop.  The
tighter the loop bandwidth the smaller the noise, but it still is there and
it shows up as phase jitter.  If you clamp down too much on the loop
bandwidth to get acceptable jitter performance then the transient response
of the loop is way too slow for making note to note transitions (portamento
anyone?).  Whether the jitter is acceptable or not is application dependent,
but it is there.

>
>Yes. And I suspect that for complex waveforms (and that's what this
>thread was about, wasn't it ?), locked frequencies might be
>musically more pleasant than beating / chorusing ones. The only
>problem I see with DCOs is that they were also widely used for
>basic traditional waveforms like saw and pulse, where you often
>want the phasing. Two completely different worlds, IMO.
>


I'm not advocating DCOs by a long shot.  They have there place as do
traditional VCOs.  However, DCOs are often given a bad rap for the wrong
reasons.  You can give them animation and neat effects like phasing if they
are just implemented and used right.  Unfortunately most of our real world
experiences comes from commercial synths that use DCOs and there the main
goal was stability, cost, manufacturability, and reliability.  Plus I
personally don't believe that some of the architects of those systems truly
understood the ramifications of their design tradeoffs to the musicallity of
their products.

Douglas R. Kraul