Subject: Re: [linux-audio-dev] LADSPA Specs ?
From: Richard Guenther (rguenth_AT_tat.physik.uni-tuebingen.de)
Date: Sun May 12 2002 - 22:14:03 EEST
On Sun, 12 May 2002, Likai Liu wrote:
> I certainly agree that envelope control can be implemented by the host
> passing dynamically changing parameters to the plugin. I have already
> given a lot of thought on that. Consider the situation of a volume
> adjustment plugin with host-controlled parameter as the envelope.
> Suppose each buffer size is 128 samples, which is reasonably small for
> dynamic parameter. When we want to do a fade-out, the host sends the
> buffer to the volume adjustment plugin, specifying a decreasing,
> negative gain each time. The problem is, for every 128 samples, there is
> a leap of the control parameter, resulting in audiable steps of the
> volume. Depending on the amount of parameter changes, this can be quite
> audiable as clicks, even more so than how linear interpolation compares
> to cubic resampling method. As Steve Harris pointed out, linear
> interpolation does not have acceptable quality. I think it's even
> pointless trying to convince him to accept the clicks caused by stepped
> host-controlled dynamic parameters. Using arrays is one of the
> extensible solutions on top of ladspa.
The easiest solution to this kind of problem (parameter change faster than
nr. of run() calls) is to make the parameter (here: the envelope) another
audio input stream - this way you get 1:1 parameter:sample mapping. The
host can be used to feed generated waves to such a port quite easily [for
GLAME we of course use another plugin for this wave generation, but that
again is not possible with LADSPA].
Richard.
-- Richard Guenther <richard.guenther_AT_uni-tuebingen.de> WWW: http://www.tat.physik.uni-tuebingen.de/~rguenth/ The GLAME Project: http://www.glame.de/
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