All audio and events that you generate in the Composer can be routed to Racks.
A Rack is a collection of plugins that process your audio and events and route it to an output.
A Rack also has an audio gain, pan and mute control that processes the audio just before the first post-fader plugin. (more on this below)
Racks are a very powerful and flexible!
For example, you can set up a Rack "Bass" to have a nice bass synth plugged in, and also a subtle audio chorus plugin that furtherly processes the bass sound.
Now you can set this "Bass" Rack to be the Target of a bass sequence part in your composition, and so all events of that sequence go to the "Bass" Rack, where the synth will make sound, and the chorus will fatten that sound 
It's important to understand that a Rack can receive audio as well as events. It depends very much on what you plug in whether this audio and events are furtherly processed.
In the above example, sending audio to Rack "Bass" won't have much effect because generally a synth plugin does not process audio input, but only event input, which it then turns into audio, i.e. the bass sounds.
At the other hand, you could setup another rack that receives events from a sequence part, with a MIDI effect plugged in (e.g. an arpegiator), and then sending the result to a hardware MIDI port so to send the resulting events to one of your external synths. Now in this case, it won't make much sense to send audio to this rack, because a MIDI effect, nor the MIDI port can do anything with the audio.
So it all depends on what you input into a Rack and which plugins are in the Rack. MU.LAB does not set any limits here, and thus you are free to make any combinations of plugins and routings of audio and event signals.
Sometimes, you might not hear what you first would expect, because audio or event signals don't come thru due to certain plugins. But if you then precisely analyse how signals flow, you'll find the reason.
The good thing about this is creative freedom!
There are so many plugins out there, some of them are pure for audio, some other are pure for MIDI events, and there also exists plugins that process both audio an events, or convert audio into events or vice versa.
MU.LAB's Racks let you PLAY with it
The Rack Window shows all used Racks.
Each Rack can be shown in an expanded or collapsed version. This can be controlled by the little button at the top left of each Rack. You can also right-click this button for more expanded/collapsed options.
Each Rack can receive audio and events from any Part in the Composer, but can also receive audio and events from other Racks! This is done by plugging in a "Send" from one Rack to another.
For example: if you want to apply the same reverb on synth A (in Rack A) and synth B (in Rack B), then send the audio from the Rack A and Rack B to a common Rack; than that common Rack will process the audio from A and B thru its plugged in reverb.
All Racks work in the same way:
- At the top there is a label that you can edit.
- Also at the top there is a little button that let you collapse/expand the Rack. You can also right-click this button to popup more contextual functionality.
- There are multiple Plug Slots, in which you can plug in a synth or effect, or plug in a Send (cfr the example above).
- At the left of these Plug Slots, there is a Pre/Post Indicator, which you can move up or down by clicking at the left of the slots.
The name Pre/Post comes from the Pre-Fader/Post-Fader analogy.
The input signal (audio and/or events) is directly processed by all plugins before the POST. Then the Volume/Pan/Mute is applied to the audio, events just pass thru. Then the signal(s) stream(s) thru the first Post plugin, and thru the following ones.
- You can double-click a plug slot to open the plug editor. Or click the "E" button at the right of it. Once a plugin editor is open, you can also use Esc to close it.
- At the right of a Send is a little knob for controlling the send gain, i.e. for controlling how much is sent.
- You can rearrange the order of the plug slots: Use shift+click and drag the slot up or down. Or you can even move it to another Rack!
- Right-click a volume slider pops up a context menu where you can assign a MIDI controller to this slider.
- Alt-click a volume slider resets it to 0 dB.
- Left-clicking the background focusses the Rack which means that any incoming MIDI is routed to this Rack.
- Right-clicking the background pops up a context-sensitive menu with more options.
- Right-clicking the output field lets you choose which type of output must be displayed: Audio or Event. Note that a Rack always has an audio out and event out at the same time, but here you choose which one is displayed. Whether the audio out and/or event out is effectively outputting a signal of course depends on what signal(s) stream thru the Rack.
- You can mute a Rack via its mute button. Right-clicking the mute button pops up a context menu with Solo and Unsolo options. Note that the mute is applied just before the first POST plug. This means that e.g. any sends before this point are still sending signal.
- When you hover a Rack plug slot, a tool tip shows what's plugged in.
| 