Subject: Re: [linux-audio-dev] LADSPA unbounded control values
From: Paul Kellett (paul.kellett_AT_maxim.abel.co.uk)
Date: Wed Nov 22 2000 - 21:14:58 EET
Paul Barton-Davis <pbd_AT_Op.Net> wrote:
>
> perhaps the problem is just with this plugin, and it should really
> specify an upper bound, which would reflect the maximum gain the
> plugin could deliver. there is still the problem of converting the
> the control value into an actual gain, since if the specified range is
> 0.0 to 1.0, what does 0.0 actually mean ? its meant to indicate
> "-infinite" gain, presumably. all very confusing.
I'm sure you know how VST plug-ins deal with this - all parameters are
0.0 to 1.0, and the plug-in can return some display text for the
parameter at the host's request. For example a gain control might do
this:
gain = pow(10.0, 2.0 * param - 1.0);
but the display would be:
sprintf(display, "%d", 40 * param - 20);
It also means that, for example, a limiter threshold control could display
values in the range -40...+20dB, or "OFF" when set to maximum.
A good control law that works well connected to a hardware knob may be
rather complicated to describe in terms of max,min,lin/exp. What about
a centre 'dead zone' in a pitch bend control? (of course this all depends
on the type of plug-in and the type of host - are you performing on a
musical instrument or setting up a technical device?).
The VST method means that the parameter values don't make any sense without
the plug-in being present to produce the "human readable" version, and it
makes it difficult to go in the other direction (if I want 6dB gain, what
parameter value do I set) but it *is* Simple.
Paul.
-----------------------------
m a x i m | digital audio
http://www.maxim.abel.co.uk
paul.kellett_AT_maxim.abel.co.uk
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