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May 6, 2010 v0.0.2 by Tim.
Understanding the Effects Rack
------------------------------
All audio track types (Input, Output, Group, Wave, Synth, and Aux) have
an effects rack into which audio plugins can be inserted in a chain.
Currently each rack can accomodate up to four plugins.
MusE currently supports LADSPA plugins and DSSI effects plugins.
One must carefully consider how many audio inputs and outputs a plugin has,
and how may channels the particular audio track has (1 mono or 2 stereo),
and how MusE uses the plugins in the rack.
MusE will try to internally create as many independent copies (instances) of
a plugin as necessary, to satisfy the number of channels in the audio track.
Basically it divides the number of track channels by the number of
plugin audio inputs or outputs to determine how many copies to make.
First it examines the number of plugin audio outputs, and if there are none,
it will examine the number of audio inputs, and if there are none,
it will simply use just one plugin copy.
For mono tracks with plugins having more than one audio input or output,
MusE uses the first input or output and ignores the rest.
For stereo tracks:
Plugin Plugin Independent Real number Real number
audio audio plugin of track of track
inputs: outputs: copies: input route output route
channels used: channels used:
-------------------------------------------------------------------
0 0 1 0 0
0 1 2 0 2
0 >= 2 1 0 2
1 0 2 2 0
1 1 2 2 2
1 >= 2 1 1 L only! 2
>= 2 0 1 2 0
>= 2 1 2 2 2
>= 2 >= 2 1 2 2
Notice that on a stereo track with a plugin having one audio input and two
audio outputs, only the first track input route channel is used (left only).
These same rules apply to inter-plugin audio when more than one plugin
is in the rack chain. Extra audio outputs of one plugin may be ignored
by the next plugin if not used.
Currently plugins with no audio outputs are not really useful in MusE,
chiefly because plugin control outputs are not used or displayed.
Nor are specialized plugins with many inputs and/or outputs.
Nor are so-called 'realtime' control plugins which use audio inputs
and outputs for control signals.
<<<
Loud noise alert! Beware of using such plugins in an audio effects rack.
>>>
Example: Consider a stereo Audio Input track with these effect rack
LADSPA plugins:
comb_splitter Comb Splitter by Steve Harris, and
tap_stereo_echo Tap Stereo Echo by Tom Szilagyi
The Comb Splitter has one audio input and two audio outputs.
The Stereo Echo has two audio inputs and two audio outputs.
The stereo Audio Input track will therefore ignore its second
input route connection. It will process the left input only,
separating it into stereo with the Comb Splitter, passing the
split stereo signal into the Stereo Echo, finally producing
stereo output available at the Audio Input track's output routes.
One improvement would be not creating unused redundant plugin copies
between plugins in stereo tracks.
For example, for a plugin having one audio input and one audio output,
feeding a plugin having one audio input and two audio outputs,
the extra copy of the first plugin is redundant and not required,
but currently it is created anyway.
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