A rack is a collection of synth and effect modules that process your audio and events and route them 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 very flexible.
They can contain synth or effect modules, or a combi of these.
For example, you plug a nice bass synth into slot 1 and a subtle distortion plugin in slot 2 to give the bass sound some extra grain.

A rack can receive audio as well as events.
It depends very much on what you plug in whether these audio and events are further 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 sound.

On the other hand, you could setup another rack that receives events from a sequence clip, with a MIDI effect plugged in (e.g. an arpegiator), and then sending the result to a hardware MIDI port so you can 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 neither 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 modules are in the rack.
MuLab does not set any limits here, and thus you are free to make any combinations of plugins and routings of audio and event signals.
There are so many possibilities, some modules are just for audio, some other are just for MIDI events, and there are also modules that process both audio an events, or convert audio into events or vice versa.
It's your creative freedom!

 

Practical Info

• Click a rack's title bar to focus it.
• Double-click a rack's name to edit its name.
• In each slot you can plug in a synth or effect module, or plug in a Send.
• A Send will send the audio and events of that slot to another rack via an auxiliary output of this rack.
  This can be used, for example, to send an amount of the audio to a common effect plugin, eg. a reverb.  
  Note that a rack can send and output only to the modules (e.g. racks) in the same modular area as the rack itself.
  So racks in the Project Modular Area can only send and output to the other modules in that Project Modular Area, racks in a MUX modular synth/effect can only send/output to the racks in that same MUX modular synth/effect. If you would need to send audio / events to another modular area then insert relevant inputs and outputs in the relevant modular areas so that the signals can stream to where you want.
• At the right of a Send is a little knob for controlling the send gain, i.e. for controlling how much signal is sent.
• If you need more slots, click the + button below the bottom slot.
  You can also right click in between 2 slots and choose "Insert Slot".
• At the right of the rack slots, there is the Pre/Post Fader Indicator.
  This indicates at what point the rack fader is doing its job.
  For example if the Pre-Post indicator is set between slots 2 and 3 then signal flows like this:

  

• You can double-click a slot to open the plug editor.
  Or click the edit button at the right of it.
  Once a plugin editor is open, you can also use Esc to close it.
• You can rearrange the order of the slots: Drag the slot up or down.
  Or you can move it to another rack.
  Or to another Composer or MUX Modular.
  Or even to another project!
• At the right side of tot rack title bar there are the rack options button and rack modular area button.
• Via the rack modular area button you get into the rack's modular area where you can see and edit the inner routings in that rack.
  Being able to edit a rack from its inside gives you great flexibility for all kinds of special cases when using multi-out plugins, side-chaining, etc.
  Make sure to read the secion below about "Modular Racks".
• Right-clicking the output field lets you choose which type of output must be displayed: Audio - Event - Modulation. Whether the audio out and/or event out is effectively outputting a signal of course depends on what signal(s) stream thru the rack.
• When choosing an output for a rack, you might not get all options because feedback loops are not allowed.
  So options that would lead to a feedback loop are not listed.
• You can drag & drop a VST / CLAP plugin file onto a rack slot.
  If it's about a new plugin it will be scanned and added to the plugin database.
• The level meter shows 3 thin lines: Top = -6dB, middle = -12dB, bottom = -18dB.
• When the mouse hovers the volume slider, the level is shown in a tooltip.
• The collapse/expand at the top-left of a rack let you toggle between small and wide view.
  You can also right-click that button for extra options.
  Shift+click that button to collapse/expand all racks at the same time.
• An expanded rack width can be changed by dragging its right border.
  Right-click its right border for a specific width-related context menu.
• A rack's context function "Render To Audio File(s)" renders all audio up to the volume fader into an audio file and puts it on a new track.
  When the rack also has auxiliary outputs, eg sends, these are also rendered in new audio tracks.
  This function can also be used for freezing synth racks and free up cpu resources, while still having practical control over the mix.
  After rendering is done, nothing is automatically muted so take care about muting the relevant tracks/rack slots so that you won't hear double audio.
  What exactly needs to be muted depends on what you exactly want to achieve.
  Each rack memorizes the used audio file name so to make it easier to update already rendered audio tracks.
   
  When editing the inner modular structure of a rack, it may be useful to add Freeze Point modules inside the rack modular structure so to have precise control over how a rack should be rendered.
  If no such Freeze Points exist then the default freeze points are the rack fader input (or if no rack fader then the main output) and the aux outputs.
• You can save your favorite racks as presets for quick and easy recall in this or any other project.
  The default location for your rack presets is the "User/Library/MUX/Racks" subfolder, aside the Effects and Instruments subfolders.
  If that subfolder also contains a "New Rack Templates" subfolder, you can save several rack presets there to be used whenever a new rack is needed.
  If it contains "New Rack.Mux" this one is your most default new rack and it will be used when you click the + rack button in a rack desk.
  If the "New Rack Templates" subfolder contains several new rack presets for your various use-cases, then Shift+click the + rack button to popup a list with all these rack presets.

 

Modular Racks

With MuLab 10 racks have become plain standard MUX Modular patches.
The thing that defines whether a MUX patch is regarded a rack or not, and thus whether it's included in the rack desk, simply is the existence of at least one Rack Slot module.
Thanks to this new modularity, racks can now have any number of slots.
Also thanks to this new rack modularity, racks are fully editable from modular side, which is handy when you want to use more complex rack routing like side-chain, multi-output synths, multi-input effects etc.
 
Eventhough since MuLab 10 racks have powerful modular options, racks are still meant as a user friendly bridge between the non-modular and the modular world.
Racks try to comfort the (non-tech) user by avoiding the need for the modular area as much as possible.
If you do edit a rack's modular inside then read these notes:

• A rack's automated modular routing, eg. when switching the pre-post fader position, assumes seriality of the rack slots.
• If you want parallel parts in a rack then best to put these in a separate MUX Modular in a slot.
  Alternatively you could use "Module Slots" instead of "Rack Slots" since "Module Slots" are not managed automatically and so they may suit better for certain custom rack setups.
• Racks use a built-in editor with an automated layout of the rack slots, pre-post fader control, fader section, etc.
  A rack can also embed a customized front panel: Open the rack modular area, from there switch to front panel mode, there click the edit front panel button.
• You can also use a rack panel in other MUX front panels and customize some options.
• The order of the rack slots on a rack's front panel is not defined by the modular routing of the rack slots (that could be too complicated, depending on the routings) but is defined by the order they were added to the modular area.
  Note you can always add a slot before/after an existing slot by right-click on the existing rack slot and choose "Insert Slot Above" or "Insert Slot Below".
  In case you manually add/copy a rack slot in the modular area it will indeed appear as the last slot.
  When right-clicking a rack slot in a rack's modular area there is the menu option "Change Slot Index".
• When a rack's modular area contains racks, these are shown as subracks.
  Subracks can be very handy to make submixes, e.g. for a drumkit.

 

Upgrade Legacy MuRack Presets

As MuLab 10 racks have become plain MUX Modular patches, no more need for separate MuRack presets.
Of course MUX Modular supports loading such legacy MuRack presets.
To show your legacy MuRack presets in the project browser, select Which = MUX Presets and Where = the appropriate folder with .MuRack files.
For quick access you could save that as a browser preset.
Alternatively if you have any custom rack presets in your user library ( = at least 1 .MuRack file), then there is a helper function in the Browser -> MUX Presets -> Options menu: "Move Legacy MuRack Presets".
This will move your legacy .MuRack presets to your M10 user library MUX/Racks subfolder.