[linux-audio-dev] Re: LADSPA Extension for Extra GUI Data

Steve Harris S.W.Harris at ecs.soton.ac.uk
Sun Jun 25 13:57:47 EDT 2006

On Sun, Jun 25, 2006 at 02:01:48 -0400, Dave Robillard wrote:
> On Tue, 2006-06-20 at 08:35 +0100, Steve Harris wrote:
> > On Tue, Jun 20, 2006 at 09:05:33 +1000, Loki Davison wrote:
> > > Because people actually use them in Om, because people actually use Om
> > > unlike certain other modulars. volt per octave is pretty damn obscure
> > > in a computer program.... If i wanted to have a cutoff at concert A
> > > what the hell is that in volts per octave?S
> > 
> > Zero typically. I have to take issue with this, 1.0f per octave is the
> > natural way to preresent things like filter cutoff in a modular. It's what
> > makes the great modular systems so easy to work with.
> Nonsense.  As a numerical unit it has no meaning whatsoever, and the
> unit actually used has no bearing on the user interface provided (which
> should of course be exponential).

It has a very specific meaning, +1.0 is +1.0 octaves.
> The only sane unit for frequency is Hz.  As Loki said, if I want a
> cutoff at concert A, I (like any musician) know that's 440Hz.  Whatever
> arbitrary ugly real number it is in "V/Oct As Defined By AMS" is not
> something I or anyone else cares to know.  Any table of frequencies, or
> math app, or damn near _anything_ that deals with frequencies will
> present it in Hz.  If you can come up with a real reason why this
> arbitrary "AMS V/Oct" makes any sense in a _digital_ modular, I'd like
> to hear it.

It's all about modulation, if I connect a [-1.0, 1.0] sine LFO to a cutoff
modulation input then I want it to modulate up and down by N octaves, not
N Hz, frequency-linearly symmetric modulations sound wrong. My favourite
(digital) modular filters have a centre frequnecy (shown in Hz, expoentialy
scaled control) and a modulation input that modulates in octaves.

You want the modulation to be musically relevent, and the most musically
useful unit for pitch is octaves :) Humans aren't SI sadly.

I agree that describing it as volts is a bit odd, but it instantly makes
people like me feel at home. There's not reason why a digital modular neds
units for its modulation sources. It's just real numbers.

- Steve

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