AU Instruments in QLab

[This Project works in QLab3 and QLab 4 but requires Plogue Bidule]

This project took  over 3 years to make work! It allows AU or VST Musical Instruments like virtual pianos and soft samplers to work inside QLab. It uses Plogue Bidule which is one of the few AU plug-ins that can host other plug-ins and allow you to connect to them via the internal IAC MIDI Busses.

Plogue Bidule will only work correctly when inserted as an effect in a Cue Output Patch. The final discovery was that QLab’s audio engine only runs if a cue with audio is actually playing. Playing a MIDI cue to the soft synth or sampler requires a dummy audio cue playing with it before you can hear the output.

Here it is in action (view full screen):


This video demonstrates one of the most useful ways in which the power of this can be harnessed. Piano music which needs to stop on cue as if the playing has been interrupted is very difficult to achieve realistically, just using a fade cue. If the stream of MIDI notes to a soft piano is interrupted then the piano will stop and decay naturally. This example goes further by slowing the playback rate of the MIDI file immediately before the stop cue. This can occur at any point in the piano music and sounds completely natural.

How it works:

Plogue Bidule is inserted as an effect in settings/patch/cue outputs



Plogue Bidule is a plugin that allows complex arrangements of audio and MIDI components to be assembled within the plugin.  Here is the plug-in programming for this example.


At the top are the unused audio inputs.

Next is an Input MIDI device which brings IAC BUS 1 into the plug in. This will be what we route the MIDI playback from a MIDI File Cue to.

This connects to our sound module or sampler. In the example I am using Pianotech 5 which is a modelled Piano.

The audio outputs of the piano connect to the audio  outputs of the Bidule plugin and hence to the QLab device routing matrix.



In the QLab workspace we have a fire all group which:

Plays the dummy audio, in the example a 2 sec silent wav set to loop

A network cue which sends an OSC message setting cue 1.01 (the MIDI file cue) setting it’s playback rate to 1.0

A load cue to set the start point of the MIDI File Cue

The Midi File Cue targeting the MIDI file we wish to playback.

When we trigger cue 2 to make the piano appear to stop naturally:

A network cue sends an OSC message with fading values to the rate of the MIDI file cue to allow it to slow down.


Then the Midi File playback is stopped and, after a suitable decay time, the dummy audio is silenced which, if no other audio is playing, stops QLab’s audio engine.


You can download the example workspace here

You will need a registered copy of Plogue Bidule Plug-in for this to work.

Pianoteq5 is available here but you can of course use any AU Instrument plug-in   instead. Synths, samplers, procedural effects generators etc.


Pianoteq is a registered trade mark of MODARTT S.A.S. France

Plogue Bidule is a trade mark of Plogue Art et Technolgie, Montreal

The Midi File used in this example is licensed under a creative commons cc-by-sa Licence from Bernd Krueger