Subject: Re: [linux-audio-dev] changing control port values with LADSPA: a serious issue?
From: Steve Harris (S.W.Harris_AT_ecs.soton.ac.uk)
Date: Mon Mar 18 2002 - 13:52:02 EET
On Sat, Mar 16, 2002 at 07:59:27 -0500, Paul Davis wrote:
> 1) set the control port value to the end point, and pray that
> the plugin will ramp to it, based on the last value.
I believe that this is the only feasible approach, you can't really go
around changing the port value as the plugin will almost certainly have
done some maths on the parameter inorder to make it usable in the dsp
core. If the plugin has the speculativly recalculate the internal value
every frame it will cost a lot of cpu.
This is what I intend with my plugins, where there are cases (I know there
are some) that you get stair stepping or zipper noise when changing
parameters I regard this as a bug, just not a particularly high priority
one.
> (2) this works is the step size is large enough. but over on the
> vst-plugins list, it seems de rigeur to interpolate at the sample
> level, something like (for linear interpolation, for example):
This is generally how you solve 1) too (think of csound c-rate). Though I
would generally use a leaky integrator, not a lerp.
> I know that LADSPA contains an "S", and I agree entirely with
> Richard's goals when he set out to find a common subset of several
> existing application-specific features for inclusion into LADPSA,
...
> Does anybody have any concrete proposals or ideas? Did I miss some
> glaringly obvious method for doing this?
Not really. I don't feel that it is a good idea to add timestamped events
or any other automation features to LADSPA.
Its one more argument in favour of a 2nd linux plugin format, whith more
features and complexity than LADSPA. I'm neutral about the idea
personally. I think I've given some thoughts about it in the past (quick
summary: it would be nice, but there's plenty left to be done with LADPSA).
- Steve
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