On 27 Jan 2009, at 01:17, achtung_999 wrote:


//skipperdy skip//

> > Most CV voltages in a modular are bipolar, with envelopes and
> keyboard
> > the most noteable exceptions. LFO's, S/H and what not all go through
> > zero. Or more correctly: *can* go through zero.
>
> Yes I know that. And that still does not answer my question really..
> Let's say we have an pseudo-ideal CV> digital converter. It would
> work from
> 0 volts to anything, so no upper limit. (Just assume this..)
> I would shift the CV up by the amount it needs to have the most
> extreme
> negative amplitude point to be 0 volts.
> Let's assume this is 5 volts. My device now tracks it nicely and
> records it
> in whichever imaginative software format we might think of.
> I now would like to use this signal to drive my modular.
> I would take the output from the software via my reverse device and
> shift
> the resulting voltages down 5 volts..
>
> In my opinion this would not be different than the original signal.
> would
> it
>

In some way you are right, yes.

There are certain CV's which don't yield the same result when "pulled
down" with a negative bias (like, say, a negative halfwave rectifier),
but that's not where your theory goes a bit wrong... It's in your
assumption that there's no upper [voltage] limit [as a way of
reasoning this through], and that the maximum required voltage is only
5 volts. Most, but not all, analog modular systems require +10V to use
their full range (pitch is a good example). This would mean that your
device should be able to output +20V to pull that voltage down to the
required maximum range of +10V (and an additional -10V to have
bipolarity). Now, what is going to happen when you don't need
bipolarity You are going to send a signal ranging from zero to +20
volts to the CV inputs of your system I'd rather not do that.

Furthermore, most modulars are hardwired [by technology] to accept a
given [bipolar] range, and a big part of the circuits and control pots
are matched to work with this. By using a "wrong" voltage to start
with, and then fiddling with it to make it match, I reckon you're
gonna end up with a big mess pretty soon.

It's pretty clear, I think, that a device like this should at least
start off with the correct range and properly engineered hardware to
make it useable and worth something.


> Sorry if I was unclear about this.
> And yes, I know it's a hassle ;-)
>

Not a hassle. Just a fascinating subject. :-)


_g