Correlation is done by mixing some of the present output of the S&H back
with the input. You need a bit of lag between the output and the input
to the mixer, so that the old output voltage holds for a moment as the
sample occurs. That is because the output will change at the instant of
the sample and you need the old output for a few milliseconds for your
mix. You can patch this up with any S&H that has a lag following it.
The MOTM-101 has a lag section. To try this, patch your random signal
(say the Pink Out of the 101) into a mixer, patch the mixer out to the
S&H input, and patch the output of the S&H to another input on the
mixer. If you patch the S&H out to the FM input of a VCO it will be
easy to monitor the effect. As you mix more of the output back to the
input, the excursions from one sample to the next will be smaller.
(There must be a mathematical formula for this.) The correlation
feature is provided in the Oakley S&H, and that's what I am asking for
in a new MOTM S&H.
You could add a DC-coupled VCA in the feedback loop. But I don't think
it would be terribly useful, due to the fact that the effect of the
correlation is subtle. The output is still random, but it has a
different pattern. I find just being able to dial it up with a knob is
plenty. Adding more VC inputs to this proposal would push it toward a
2U size, and most people seem to prefer 1U. You can always patch a VC
feedback loop.
-Richard Brewster
jwbarlow@... wrote:
> In a message dated 1/1/2006 4:50:04 P.M. Pacific Standard Time,
> jloffink@... writes:
>
> S&H Correlation is typically implemented as a lag circuit prior to the
> sample and hold.
>
> I haven't kept up with all the permutations of this module, but I'm a
> big fan of this correlation feature and think that it should be a VC
> function too.
>
> JB