Subject: RE: [linux-audio-dev] New LADSPA Version - Issues Resolved?
From: David Olofson (david_AT_gardena.net)
Date: to maalis 09 2000 - 21:11:38 EST
On Thu, 09 Mar 2000, Richard W.E. Furse wrote:
> From: Richard Guenther [SMTP:richard.guenther_AT_student.uni-tuebingen.de]
> [...]
> > Another question regarding to the pulgin API or the general structure of
> > supported networks: How can one handle feedback
> > - inside a plugin (without copying to a "local" buffer)
> > - from different plugins, i.e. plugin 2s output is fed back to plugin 1s
> > input?
> [...]
>
> Plugins using internal feedback (e.g. delay lines) are expected to do this
> using internal memory.
>
> Feedback loops in the host's network are beyond the scope of this API. The
> host may be able to get around this anyway - MN currently supports flow
> graphs with cycles under certain conditions and it will be possible to use
> LADSPA plugins within these cycles as long as those conditions are still
> met.
To set up a feedback loop correctly, you basically need two things:
1) You need to know the internal processing delay of each plugin
involved. (Meeeeep: All plugin APIs I've seen so far fail here!)
2) You need to be able to use a sufficiently small buffer size
to handle the desired delay of the loop.
By chosing the biggest usable buffer size that is net_buffer_size/N
(N=1, 2, 3,...), and adjusting to the correct delay by inserting a
delay on the feedback line, this can be done as an isolated "cell"
within the net.
Except for failing the first requirement (just as most other APIs -
a fact that actually *does* annoy users in real life situations!),
LADSPA should have no problems with this.
//David
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