[LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO)

David Robillard d at drobilla.net
Wed Aug 22 21:32:26 UTC 2012

On Wed, 2012-08-22 at 21:12 +0000, Fons Adriaensen wrote:
> On Wed, Aug 22, 2012 at 12:43:27PM -0400, David Robillard wrote:
> > Particularly for those who play along with real instruments, making sure
> > we have sensible tunability is important.
> In fact none of the classical VC synths had anything close to
> absolute tuning, in the sense that you could accurately set
> them to some frequency without using a frequency counter, or
> comparing with another signal. They had to be tuned just like
> you tune e.g. a string instrument. And most were notoriously
> unstable as well.

Well, sure.  We are throwing the word "absolute" around a lot, all I
mean is "a voltage means some frequency".  The mapping is not entirely

*Everything* is relative if you really get down to it :)

> > Fons can perhaps explain it in detail, but I believe there are good
> > reasons why these plugins need to use logarithmic frequency inputs.  The
> > attempts at faithful implementations of the Moog filters in particular.
> It is not necessary in order to have the 'moog' sound - the typical
> distortion, the way it detunes when overdriven, and the 'noisyness'
> (which the plugins don't emulate). 
> You need the logarithmic control to emulate the 'look and feel',
> of a complete analog modular synth, to allow the user to combine
> modules in similar ways as could be done on the real thing.

The ability to modulate with octaves is definitely nice.  I agree with
that choice, it tends to more musical results particularly when you
start tossing audio and CV around interchangeably.  It's not so nice for
setting the frequency to a particular note, though.

The oscillators actually have three CV frequency ports: frequency, lin.
FM, exp. FM.  Since the FM ports provide the ability to modulate in a
moogey way, I'm thinking perhaps the ideal solution (outside AMS) is to
simply make the frequency port Hz and leave the others as-is.  The
others, being FM, are purely relative.

The filters are slightly different: they also have two CV FM ports (lin
and exp), but the cutoff frequency is a control port (not CV).  It might
be nice to make this CV as well, space be damned.  This one port could
also be Hz, leaving the others alone.

Since these plugins have explicit FM ports, which is what makes them
nice to play with in a modular in the first place, nothing seems to be
lost by making the one absolute port in Hz and making all these
questions go away.

Sound reasonable?


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