M9 Docs   Rack

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. 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 further processes the bass sound. You can then set this "Bass" rack as the target of a bass sequence clip in your composition, so that 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 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 sounds.

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. The app does not set any limits here, and thus you are free to make any combinations of plugins and routings of audio and event signals. At first you might not always hear what you would expect, because audio or event signals don't come thru due to certain modules. 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 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. Play around with it

More Info

  • Click a rack's name to focus it.
  • Double-click a rack's name to edit its name.
  • There are 6 slots, in which you can plug in a synth or effect modules, or plug in a Send.
  • At the right of these slots, there is the 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 modules 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. 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.
  • 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 slots: Drag the slot up or down. Or you can move it to another rack. Or to another MUX Modular. Or even to another project!
  • Alt+click a slider/knob steps thru its main values, cfr the User Interface page.
  • 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.
  • When you hover a rack slot, a tool tip shows what's plugged in.
  • 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.
  • If a certain rack slot plugin uses more than one input/output,
    you can export these auxiliary inputs/outputs as rack inputs/outputs via that slot plugin's context function "Setup Aux Ins/Outs".
    If you do so then the aux inputs/outputs will appear as extra rack inputs/outputs in the modular area.
    This is especially useful for multi-out plugins (eg. drum machines) and for setting up side-chaining.
  • 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.
  • 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.
  • 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. That's also the reason why this can't be automated. Each rack memorizes the used audio file name so to make it easier to update already rendered audio tracks.
  • When creating a new rack and you have created a New.MuRack preset file in the User/Library/Rack sub-folder, then that preset file will be automatically used as a template for the new rack.

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