[linux-audio-dev] ladspxmlgui needs numeric input controllers

Alfons Adriaensen fons.adriaensen at alcatel.be
Wed May 14 06:37:00 UTC 2003

On a somewhat related topic: there's one thing I'm missing in the
LADSPA parameter hints. Sometimes you need a control that is
logarithmic, but that does go down to zero. Fer example, the
frequency modulation gain of a VCO needs very small values for
things as vibrato, large values for FM synthesis, and at the
same time you want to be able to swicth it off without disconnecting
the source.

If 0 <= p <= 1 is the 'slider position', and a, b are the parameter
limits given in the hints, and x the parameter value, then a linear
control does

x = a + p * (b - a)

and a logarithmic one does

x = f (p) = a * epx (p * log (b / a).

Could we add a hint bit saying that the mapping should be

x = p * f (p), with f (p) as above ?

Another useful bit would be one saying 'display in dB'. Combined with
the other one, this would give a reasonable fader.



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