[Pd] Pd to CV for a Moog (OT)

[Chuckk Hubbard]

Instead of adding more portamento for finer pitch resolution, would it
be possible to do different registers separately?  Since I intend to
compose the entire piece before passing it through the Moog, and my
patch handles all the tempos, it would not be a problem to record the
audio in segments and line them up in Pro Tools.  I suppose the
wandering tuning of the synth itself will be an issue.

I like your very last suggestion.  I realized through some preliminary
investigations with a multimeter that my soundcard removes DC pretty
quickly.  I guess your point about the 22kHz constant frequency is
that this would not happen.
For the op-amp idea, would a signal not be sufficient?  I thought
[sig~ .4], for instance, would output a constant value of .4?

Another thing I didn't mention is that the only computer in the same
room as the Moog is a university Mac, which I won't be able to tear
open.  I don't yet own a working laptop, so if anything like that
needs to be done, it will be me bringing my PC to school.  I think
this will still be easier for me than the PWM squarewave, which I
still don't understand.

Thanks for your help.

-Chuckk


On 9/11/06, Martin Peach <martin.peach at sympatico.ca> wrote:
> Chuckk Hubbard wrote:
> > On 9/11/06, chris clepper <cgclepper at gmail.com> wrote:
> >> Pitch to CV, Envelope Followers and Gates might be of use.
> >
> > I saw something about envelope followers online.  It seems like that
> > ought to do it, with some manual adjustments as always.  Pitch to CV I
> > would love to do, I have no idea how.
> > Also, a friend suggested generating PWM from my serial port and
> > filtering it.  I don't know exactly how a Moog's PWM works, but from
> > his description I thought I might just as well generate sine, ramp,
> > square, triangle and pulse waves in Pd and run them through the
> > filters and envelopes on the synth.  And where's the fun in that?  But
> > if no other possibilities work out, I can use that.
> You can generate control voltage from a pulse-width modulated square
> wave in pd. Put an envelope follower circuit on the soundcard output and
> probably some more gain. You can do that with a quad op-amp. Problem is
> ripple in the output that can be mitigated at the cost of more portamento.
> The more resolution you want the lower the PWM frequency has to be for a
> fixed sample rate.
> That's maybe not a problem for 12 notes per octave but microtonality
> needs more precision, so the base frequency will drop and so your
> lowpass filter needs to go lower still and then your notes tend to glide
> a bit going from one to the next or else you get FM from the PWM frequency.
> Another way to do it is to output something like 22kHz constant
> frequency wave but vary the volume. Then the low-pass filter can be
> around 1kHz and you can get thousands of levels with a 16bit soundcard.
> You might be able to do the envelope follower with just a diode and a
> capacitor but a better solution would use op-amps to buffer the voltage.
> If you're doing something that relies on precise tuning you ought to
> make a good cv generator. I built my own MIDI to CV (and gate and trig,
> don't forget) converters that use a PIC16F628 and a 16bit DAC for 65536
> levels on 0-10V for my analog synths, for less than $50 parts. You could
> also interface a serial DAC to an arduino.
> But I bet you could do it with a cheapo soundcard as well if you can
> find the output of the dac before it passes through any capacitor. You
> need to pass that through a simple op-amp amplifier to add gain and
> offset to get from +-1V  to the 0-10V range. Then write a dc external
> for pd that outputs a constant value instead of a signal (maybe line~
> already does that).
>
> Martin
>