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# Understanding the effects rack

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 inputs | outputs | copies | track in route channels | track out route channels
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 specialized plugins with many inputs and/or outputs are not really useful in MusE.

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
- 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.