Dec 14, 2019 v0.0.4 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 accommodate up to eight plugins.

MusE currently supports LADSPA plugins and DSSI effects plugins,
 and LV2 and VST 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 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, 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.
  
  
