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

Steve Harris S.W.Harris at ecs.soton.ac.uk
Mon Jun 26 08:04:20 UTC 2006


On Sun, Jun 25, 2006 at 04:21:20 -0400, Dave Robillard wrote:
> > 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.
> 
> This is true, but there are other cases when you want a real, meaningful
> frequency to do something with (using the same plugin).  Eg lowpass all
> frequencies above 800Hz.  Someone working on a DAW definitely doesn't
> want to deal with this meaningless V/Oct unit.

That's why I said you have a centre frequency control, that's set in Hz.
 
> Of course, in a modular you can convert Hz frequencies to VOct
> frequencies, and in a DAW you can convert VOct frequencies to Hz, but in
> both cases it's a user nuisance, so it needs to be automatic.  My gripe
> isn't with the unit itself, so much as in the current situation with
> LADSPA it's a really, really huge PITA to have a mess of twisty little
> units, all alike.

Yes, but neccesary, unless your hosts all understand the semantics of
pitch/frequency and are willing to do lots of pow() based conversions.
 
> Of course LV2 will let us solve this, and the frequency unit can in both
> cases be kept entirely transparent by the host (if you want), making the
> actual unit used by a plugin just an optimization as it should be
> (skipping the conversion step).

s/will/could/, I'm not yet convinced that it's appropriate. My preference
would still be for a Hz centre control and a (high rate) modulation input.
If there's a sane representation in RDF for a single port to do both
things well, then I'm all for it, but I'm scpetical.

- Steve



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