Subject: RE: [linux-audio-dev] Reference amplitudes and LADSPA (again)
From: Kai Vehmanen (kai.vehmanen_AT_wakkanet.fi)
Date: Sat Feb 02 2002 - 17:02:59 EET
On Sat, 2 Feb 2002, Richard W.E. Furse wrote:
> Perhaps we should include a flag on LADSPA plugins indicating that the
> plugin is non-linear and therefore cares about input level, plus a
> recommendation that such plugins expect peak amplitude around 1. This gives
Just stating that 0dB level is 1.0f, and adding [-32767,32767] ->
[-1.0,1.0] scaling to applyplugin, is not a bad option either. For a host
to do on-demand scaling of audio data, it would have to maintain knowledge
of the original fixed-point value range while traversing through the
plugin network. Might save a few cycles, but doesn't sound like a very
good design idea to me.
> I don't think this should be much more than a recommendation - some plugins
> inevitably mess around with peak levels and forcing plugins to keep to these
> levels (a) breaks relative scaling when processing two channels of stereo in
> parallel and (b) is very artificial and (c) inefficient - a chain of linear
> plugins may mess around with signal amplitude quite badly and it'll be much
> more efficient to renormalise at one point in the chain rather than on each
> plugin.
Absolutely. In networks of plugins, normalization should only be done when
changing to/from fixed value range representation, or inside plugins
(limiters and others).
-- http://www.eca.cx Audio software for Linux!
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