A Plug In Primer

EXAMPLE 6: STOP with REVERB TAIL Using AUMatrixReverb.

The final example of audio effects in audio cues is the classic ‘stop with reverb tail’ effect. This is a quick way of ending music cues quickly and cleanly, on cue, at any point in their length without using more advanced techniques like devamping. Here’s a screen recording of a cue stopped in various places:

The main cue has a little reverb applied, otherwise, the contrast with the tail section can be too great. When the STOP AND REVERB cue is triggered the original cue is stopped and a fade cue snaps up the wet mix of the reverb rapidly.

This utilizes the feature of the fade cue that allows all parameters of plug-ins to be changed from the original value to another in the time of the fade. Finally, the cue is manually hard stopped, using an OSC cue delayed by the length of the reverb tail.


A Microphone cue must have its input and output on the same device. The patches and defaults for microphone cues, in settings, have their own page and are independent of the audio cue settings. Here are  a couple of cues set up with two reverbs, AU Matrix Reverb and a freeware plug-in:

Both plug-ins fail to apply an effect to the audio. The shareware reverb passes no audio, and AUMatrixVerb just passes the original audio.

This is because the effects are now presented with a multichannel input, equivalent to the number of hardware input channels on your interface.

Very few reverb plug-ins will work in this configuration, which is unfortunate, as putting some reverb on a mic is a common use for QLab’s audio effects feature.

Here is a shareware reverb again, but this time a 2 input channel interface (MBox2) is patched, instead of the 10 channels (Octacapture) in the original example:

With a 2 input interface these plug-ins both work as expected. This variation between interfaces is the cause of some confusion. One user may recommend a plug-in that another user can’t get to work, all because they are using interfaces with different numbers of input channels.

For microphone cues in QLab 4.1 you can set the number of channels a Mic cue uses and the channel start number to match the number of channels the plug in will work with. It is therefore possible to use Matrix reverb on a single channel. If you don’t need to use all your interface’s mic inputs you can use odd number inputs only to get a mono to stereo  reverb . (Although it may sound slightly different to when it is used with both inputs driven.) It is important to ensure that even number channels have their mic gins at minimum so you do not feed preamp noise into the unused channel

Matrix Rvb Stereo

If you need to use all your mic inputs you can get a mono reverb using these settings.

Matrix Rvb Mono

Testing Plug-ins for Audio and Mic Cues

Generally, if a plug-in will work with a given number of physical inputs on an interface with a microphone cue, it will also work with an interleaved audio file, with an equivalent number of tracks. Plug-ins can, therefore, be tested easily using multitrack audio files.

You can download a set created for this purpose here. The files consist of spoken channel number idents on each track. They are intended to be looped.

EXAMPLE 9:  CUES Using AUPitch and Effects Fades.

Here is a plug-in that will interface with high channel counts, either as interleaved audio tracks or interfaces with lots of microphone inputs:

Tracks 1 and 24  of a 24 ch interleaved wav are audible, with an AU pitch shift plug-in on the cue audio effects tab. When the fade is triggered the pitch parameter of the plug-in is faded to a new value, and the matrix crossfades, reversing the sides of the 1 and 24 track announcements.

RECAP: Plug-Ins in Cues’ Audio Effects Tab 

Plug-ins may not report their tail times, and may cut abruptly, or not release the cues without being explicitly hard stopped, either with a double ESC, or an OSC hardStop cue.

Plug-ins may only work with a specific number of inputs, either as interleaved tracks in an audio cue, or as inputs on a hardware interface.

A cue list that includes cues with audio effects that plays perfectly on a system that uses an interface with a small number of input channels, may not play at all on a system with a more complex interface with a higher input count.

Plug-ins that do not work may produce no audio output, or may just pass through the original audio unaffected.

Plug-ins may be slow to load, and there may be a delay before the effect is heard on the audio cue.

Meters don’t work on plug-ins inserted in cues.


Many of the above problems can be avoided by inserting plug-ins on cue outputs, or on device outputs. There, they behave far more like plug-ins in a DAW, or effects on aux busses in a mixer, in so far as they are loaded when the workspace is opened and stay unchanged until the workspace is closed.

There are some disadvantages:

Plug-in parameters are beyond the control of QLab cues. Parameters can’t be faded or changed . So, for instance, if you need a long and short reverb, you will have to create 2 separate reverbs.

The outputs of the effects are permanently live to the outputs of the system. This precludes the use of effects with, for instance, simulation of 50/60Hz mains hum, vinyl surface noise, or integral sample playback.

However, one great advantage is that the meters work, so it is even possible to have spectrum analysers on output inserts, as well as having proper visual feedback when setting up multiband dynamics units, etc. On the following pages is a step by step guide to setting up the inserts, and some examples of the plug-ins in use.

EXAMPLE 10: AUMatrixReverb on a Stereo Cue Output

This example inserts a stereo reverb on some high numbered cue outputs, beyond the range of actual physical outputs in use, in this case, 17-18, and routes the output of that reverb to audio outputs. using the device matrix.

Step by Step:

Go to settings/Audio/EditPatch/Cue Outputs and select 2 channels from the pop-up menu on ch 17


Add Effect Apple AUMatrixReverb


Select preset on plug-in preset menu,


Open the Device Routing tab and matrix cue outputs 17+18 into the required audio outputs. In the example, 1+2 are used so the reverb goes to the main audio outputs. For a reverb, -20 is a good level. This creates the equivalent of a reverb return on a console or DAW.


Return to the cue list and create an audio cue and matrix the cue to cue outputs 17+18.


Preview the cue (press”V”) and adjust the reverb send levels using sliders 17+18

Reverb Send

Now create a microphone cue. You will probably notice that sliders 17+18 are inactive and greyed out. This is because the patch edit for microphone cues is entirely independent of that set for audio cues. Go back to settings and click the edit patch button for the Microphone cues and repeat the steps to insert a stereo instance of AUMatrixReverb and select the preset.


And matrix the cue outputs to your audio outputs in Device Routing


Go back to the cue list,  preview the microphone cue (by pressing “V”), and adjust the reverb send using sliders 17+18 to taste

. Mic cue

You now have functioning reverb within QLab that is free of most of the problems associated with plug-ins directly inserted on audio or microphone cues.

EXAMPLE 11:  Inserting Delay On Device Outputs

It is often desirable to time delay certain loudspeakers on a rig.  This can achieve far greater realism for performers wearing lavalier microphones, by ensuring the direct sound from the performer reaches the audience very slightly before the reinforced sound from the loudspeakers.

For recorded sound, it is a very powerful tool, as it can alter the perceived location of the source of the sound. At it’s simplest it can prevent those sitting close to speakers on the proscenium arch being aware of sound coming from the loudspeaker itself. If the audio is played through the proscenium speakers and also through speakers at the rear of the stage, introducing 20ms of delay on the proscenium speakers can move their apparent position to an on-stage position while maintaining the clarity of a loudspeaker in the auditorium.

In this example, we will insert a time delay and a graphic EQ to allow delay and EQ of the loudspeaker systems connected to outputs 1+2 of our interface.

Open settings/audio/edit patch and select 2 channels in Device output 1

device patch

Insert an Apple AUSampleDelay and an AUGraphicEQ plug-in to the device output. In our example, the sample delay is set to 882 samples which equates to 20ms of delay at 44.1KHz. On the graphic, a couple of troublesome frequencies are adjusted a little.

device inserts

Now, all audio that comes out of outputs 1+2 of the interface will be processed by the plug-ins.

Important Note:  Although called device outputs, this processing is actually considerably downstream of the actual physical device outputs, so you still need to set this up for microphone cues and audio cues separately. Of course, the advantage of this is that you can have completely different settings for each cue type.

You can download a full bundle of this workspace with the audio here.

Chapter Author: Mic Pool

Chapter Graphic: Original photograph By Lionel Allorge via Wikimedia Commons.
Licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
Modified image distributed under the same license.
Creative Commons License

Music in Demo Video: “Protofunk”
Kevin MacLeod (incompetech.com)
Licensed under a Creative Commons Attribution 3.0 Unported License Creative Commons License