You press GO.
The cue starts.
The playhead moves and QLab’s meters show audio.
But nothing comes through the sound system.
If you work with QLab for long enough, you will see this at some point.
The good news is that QLab audio problems become much easier to find once you stop changing settings at random and start following the signal.
In a theatre, I treat QLab exactly as I would any other part of the sound system.
I start at the source and follow the audio until I find the point where it disappears.
The basic signal path looks like this:
Audio file → Audio cue → Cue output → Audio output patch → Mac audio device → Audio interface → Mixing desk → Loudspeaker system
In this guide, I’ll explain how QLab 5 audio routing works, how to connect QLab to your sound system and the troubleshooting order I use when QLab appears to be playing but nobody can hear it.
QLab Playing But No Sound? Check These First
If you are standing in a theatre with a show about to start, you probably do not want a lesson on matrix mixers.
Start with these five checks.
- Is the QLab cue producing audio?
- Is the cue assigned to the correct audio output patch?
- Is the audio output patch connected to the correct device?
- Is QLab sending audio to the correct physical outputs?
- Is the sound reaching the correct input on the mixing desk?
If you work through those questions in order, you will solve a large percentage of QLab playback problems.
The important part is the order.
Do not start changing desk routing, QLab settings and interface software at the same time.
Find where the signal stops.
How QLab Audio Routing Works
QLab 5 uses two main stages of routing before audio reaches the output of your Mac or audio interface.
Figure 53 describes these as the cue matrix mixer and the patch matrix mixer.
The cue matrix controls where audio from an individual cue goes.
The patch matrix then takes those cue outputs and routes them to the outputs offered by your selected audio device.
So a simplified QLab signal path looks like this:
Audio file
↓
Audio cue
↓
Cue matrix mixer
↓
Cue outputs
↓
Audio output patch
↓
Patch matrix mixer
↓
Device outputs
↓
Audio interface
From there, QLab has finished its job.
The audio might then travel into a sound desk, system processor, amplifier or loudspeaker depending on your setup.
Figure 53 confirms that each audio-producing cue has its own cue matrix. That matrix feeds the patch matrix belonging to the audio output patch selected for the cue. The patch matrix then feeds the outputs of the selected audio device.
Source: https://qlab.app/docs/v5/audio/introduction-to-audio/
Understanding this signal path is one of the most useful things you can learn in QLab.
Once you understand it, “QLab has no sound” stops being one big problem.
It becomes a series of smaller places you can test.
What Is a QLab Audio Output Patch?
An audio output patch sits between your cues and the physical audio device connected to your Mac.
Think of it as the routing layer between your QLab workspace and the outside sound system.
Your patch tells QLab which device to use and how QLab’s cue outputs connect to the outputs offered by that device.
Your device might be:
A Mac headphone output
A USB audio interface
A Thunderbolt audio interface
A Dante device
An AVB device
Another macOS-compatible audio device
For a simple rehearsal setup, your patch might send stereo QLab playback directly to the Mac headphone socket.
On a theatre production, the same principle might send eight, sixteen or more outputs from QLab into separate channels on a sound desk.
The principle does not change.
Only the size of the system changes.
Cue Outputs and Device Outputs Are Not the Same Thing
This is one of the areas where beginners often become confused.
A QLab cue output is not necessarily a physical socket on your audio interface.
Cue outputs exist inside QLab.
Device outputs belong to the audio device selected in your output patch.
The patch matrix connects one to the other.
Imagine your QLab Audio cue has two channels.
Left and right.
You might route:
Audio channel 1 → Cue output 1
Audio channel 2 → Cue output 2
Your audio output patch then routes:
Cue output 1 → Device output 1
Cue output 2 → Device output 2
If device outputs 1 and 2 correspond to physical outputs 1 and 2 on your interface, those signals then leave the Mac through those connections.
But QLab gives you far more flexibility than a simple one-to-one connection.
You could send one cue output to several device outputs.
You could send several cue outputs to one device output.
You could also change the level at individual crosspoints within the matrix.
This is where QLab becomes far more useful for theatre than a basic stereo playback application.
How to Set Up Basic Stereo Playback in QLab
Start with the simplest possible setup.
Get one stereo audio file playing correctly before building anything more complicated.
Create an Audio cue and select your audio file.
Open the cue’s Audio Levels settings.
For normal stereo playback, the left channel should feed one cue output and the right channel should feed another.
Next, check which audio output patch the cue uses.
Open your workspace audio settings and make sure the patch has the audio device you want to use.
For a basic setup, that might be the Mac’s built-in output.
Then check the patch routing.
A simple stereo configuration could look like:
Cue output 1 → Device output 1
Cue output 2 → Device output 2
Play the cue.
If you now hear audio, you have established the basic signal path.
Do this before adding complex routing.
It gives you a known working starting point.
If you are learning QLab for theatre, this is also the point where things start getting more interesting. Basic stereo playback is only the start. A professional theatre setup often uses multiple outputs, dedicated desk channels and routing designed around how the show will be operated.
My QLab for Theatre course will cover this complete workflow, including multi-output playback, show templates, programming and live fault finding.
How to Connect QLab to an Audio Interface
The next step is replacing the Mac’s built-in output with an external audio interface.
Connect the interface to the Mac and confirm macOS recognises it.
Then open QLab and select that device in your audio output patch.
Do not assume that plugging the interface into the Mac automatically means QLab will use it.
The output patch needs to point to the correct device.
Once selected, look at the device outputs available within the patch.
A four-output interface should normally present several available outputs to QLab.
Your routing might then look like this:
Cue output 1 → Interface output 1
Cue output 2 → Interface output 2
Cue output 3 → Interface output 3
Cue output 4 → Interface output 4
Those outputs could then connect to four channels on your sound desk.
One important point here is that some audio interfaces have their own routing software.
QLab might send audio correctly to a device output while the interface’s internal mixer routes it somewhere else.
Figure 53 specifically points out that QLab only knows what the Mac reports about the device. Some hardware then performs additional routing after QLab.
If everything looks correct inside QLab but the interface still produces no audio, check the manufacturer’s control software.
How to Send QLab to Separate Sound Desk Channels
This is where QLab starts fitting into a professional theatre workflow.
Instead of sending everything from QLab as one stereo pair, I often want different types of playback arriving at different channels or inputs on the sound desk.
For example:
QLab output 1 → Desk channel 31
QLab output 2 → Desk channel 32
QLab output 3 → Desk channel 33
QLab output 4 → Desk channel 34
You might then decide to use those channels for different purposes.
For example:
Outputs 1 and 2 → Music playback
Outputs 3 and 4 → Sound effects
Output 5 → Click
Output 6 → Onstage effects
Outputs 7 and 8 → Additional playback or specialist routing
The exact setup depends on the production.
The important point is that QLab does not have to appear at the desk as one stereo source.
Separating playback gives the sound operator more control.
It also makes fault finding easier.
If a sound effect is missing but music playback still works, you immediately have more information about where the problem might sit.
You can read more about how signals are handled at the desk in my Live Sound Mixing Techniques guide:
https://robsummers.co.uk/live-sound-mixing-techniques/
Why QLab Meters Move But No Sound Reaches the Desk
This is one of the most confusing QLab problems when you first encounter it.
You press GO.
The cue runs.
You see meters moving.
Yet nothing reaches the console.
The reason is simple.
A meter only tells you that audio exists at that point in the signal path.
It does not prove the audio successfully travelled through everything after it.
For example, an Audio cue might be playing perfectly.
But the cue could be assigned to the wrong output patch.
Or the output patch could point to an interface that is no longer connected.
Or the patch matrix might send the signal to the wrong device output.
Or the interface’s own routing software might send it somewhere unexpected.
Or the correct QLab output might arrive at desk channel 31 while you are looking at channel 32.
The moving meter proves one thing.
The cue contains audio and QLab is processing it at that point.
You still need to follow the rest of the signal.
QLab No Sound Troubleshooting: Follow the Signal
When QLab stops producing sound, this is the order I would use.
1. Check the Source File
Start with the obvious.
Does the file contain audio?
Play another known working cue.
If every cue has stopped producing sound, the problem probably sits further down the signal path.
If one cue fails while everything else works, start with that cue.
This distinction saves a lot of time.
2. Check the Audio Cue
Look at the cue.
Is it running?
Is the playhead moving?
Are you seeing audio activity?
Check its level settings.
Look for anything muted or turned down.
Also check the routing inside the cue matrix.
You want to establish whether audio is reaching the cue outputs.
3. Check the Cue’s Audio Output Patch
Look at which patch the cue uses.
This is easy to overlook when you have several output patches in one workspace.
A cue copied from another workspace might still reference a different patch configuration.
A cue might also have been deliberately routed somewhere else during programming and never changed back.
Confirm the cue uses the output patch you expect.
4. Check the Audio Output Patch
Now move one stage further down the system.
Open the audio output patch.
Check the selected device.
Figure 53 identifies several common output patch problems, including:
No device being selected.
A device being unavailable.
A device appearing without usable output channels.
Source:
https://qlab.app/docs/v5/audio/audio-output-patch-editor/
Do not ignore warning indicators inside QLab.
They exist for a reason.
5. Check the Patch Routing
If the correct device is connected, inspect the patch matrix.
Confirm your cue outputs feed the device outputs you expect.
For example:
Cue output 1 → Device output 1
Cue output 2 → Device output 2
It is easy to build a perfectly functioning Audio cue which then feeds a device output that goes nowhere useful.
This becomes especially important on interfaces with large output counts or Dante systems.
6. Check the Audio Interface
Now leave QLab.
Does the interface show signal?
Does it have output meters?
Does it have its own mixer or routing application?
If QLab sends audio to output 5 but the interface software routes output 5 somewhere else, changing your QLab cue will not fix the problem.
This is why you need to know the whole playback system rather than only knowing the software.
7. Check the Mixing Desk
Next, move to the desk.
Is the expected channel receiving signal?
Check:
Input patch
Channel mute
Fader
DCA or control group
Channel routing
Groups
Matrices
Output routing
At this stage, QLab might be working perfectly.
You are now fault finding the sound system.
If you want more detail on console workflow, see:
https://robsummers.co.uk/mixing-for-musicals-a-practical-guide/
8. Check the Loudspeaker System
If signal leaves the desk but you still hear nothing, keep moving forward.
Check the output processing, amplifiers and loudspeakers.
Again, follow the signal.
Do not go back to QLab because you have run out of ideas.
If QLab sends audio correctly and the desk receives it correctly, QLab is not your problem.
Use the QLab Workspace Status Window
QLab’s Workspace Status window is another useful troubleshooting tool.
It gives you a central place to see problems within the workspace rather than hunting through individual cues.
Figure 53 describes the window as a way of identifying warnings and errors which could affect the workspace.
Source:
https://qlab.app/docs/v5/tools/workspace-status-window/
Make checking the Workspace Status window part of your troubleshooting routine.
It becomes especially useful as your show file gets larger.
A ten-cue rehearsal workspace is easy to inspect manually.
A large theatre production containing hundreds of cues is another matter.
What Happens When QLab Loses an Audio Device?
One of the most common causes of sudden routing problems is a missing audio device.
Perhaps someone disconnected the USB interface.
Perhaps the device was switched off.
Perhaps the Mac restarted before the interface.
Perhaps a Dante configuration changed.
QLab still has the workspace.
Your cues still exist.
The routing you programmed still exists.
But the destination device is no longer available in the way QLab expects.
This is why a show machine should not be treated like somebody’s everyday laptop.
A theatre playback system needs a repeatable startup procedure.
Power devices in a consistent order.
Confirm the audio interface.
Open the workspace.
Check the output patch.
Check Workspace Status.
Test playback.
Then move on.
Five minutes spent checking the system before a session starts is preferable to diagnosing it with a director and company sitting in the auditorium.
A Professional Theatre QLab Routing Example
Let’s take the same idea and apply it to a larger theatre system.
You have a Mac running QLab.
The Mac connects to a multi-output audio interface.
That interface feeds a DiGiCo or Yamaha console.
The signal path might look like this:
QLab Audio cue
↓
Cue matrix
↓
QLab outputs 1 to 8
↓
Audio output patch
↓
Interface outputs 1 to 8
↓
Eight inputs on the sound desk
↓
Console groups and matrices
↓
PA system
I would label everything clearly.
Do not leave yourself with:
Output 1
Output 2
Output 3
Output 4
Give those outputs names which tell you what they do.
The same applies at the desk.
The person fault finding the show at some point might not be the person who programmed it.
Good naming speeds up fault finding.
The same applies to cues.
“Cue 153” tells me almost nothing.
“Door Slam SR” gives me information before I have even opened the cue.
This matters more as the production grows.
Good QLab programming is not only about making the show work today.
It is about making the workspace understandable tomorrow.
Do You Need the QLab Audio Licence?
QLab provides audio features at different licence levels.
Basic audio playback is available without buying the full Audio licence, while more advanced audio functionality requires an appropriate licence.
Because Figure 53 updates licensing and feature availability over time, check the current feature comparison before planning a system around a particular function.
The current licence feature table is here:
https://qlab.app/docs/v5/general/features/
This is especially important if you are building a multi-output theatre playback system on a machine which has never run the show before.
Do not find out during the fit-up that a function you planned to use needs a licence you do not have.
Build a Reusable QLab Audio Setup
Once you have a routing configuration that works, do not rebuild the whole thing from memory for every production.
Build yourself a clean starting workspace.
For example:
Output 1 → Playback Left
Output 2 → Playback Right
Output 3 → FX 1
Output 4 → FX 2
Output 5 → Click
Output 6 → Stage
Output 7 → Spare
Output 8 → Spare
Set up sensible naming.
Create test cues.
Label your patches.
Document which QLab outputs arrive at which desk inputs.
Then save the workspace as a starting template.
Every production will need changes, but having a known working starting point removes unnecessary setup work.
It also gives you something useful when fault finding.
If your test cue works but your show cue does not, you have already narrowed the problem.
My QLab Pre-Show Audio Checklist
Before opening the house, I would check:
- Correct QLab workspace open
- No unexpected warnings in Workspace Status
- Correct audio interface connected
- Correct audio output patch selected
- QLab outputs mapped correctly
- Interface routing correct
- Desk inputs receiving the expected QLab outputs
- Playback channels routed correctly through the desk
- Known test cue plays correctly
- Critical show cues checked
If your show uses multiple playback outputs, test every output.
Do not play one stereo cue and assume output 7 works.
Send something through output 7 and prove it.
The same principle applies to spare outputs.
A spare is only useful if it works when you need it.
QLab Audio Routing Frequently Asked Questions
Why is QLab playing but there is no sound?
If the cue runs and QLab shows audio activity, follow the signal from the cue towards the sound system.
Check the cue matrix, audio output patch, selected audio device, patch routing, audio interface and mixing desk.
Find the last point where audio exists.
The fault sits somewhere after that point.
What is an audio output patch in QLab?
An audio output patch connects QLab’s internal cue outputs to an audio device available to your Mac.
The patch also contains routing between QLab’s cue outputs and the outputs offered by that device.
What is the difference between a cue output and a device output?
Cue outputs exist inside QLab.
Device outputs belong to the selected audio device.
The patch matrix routes cue outputs to device outputs.
They do not have to use a one-to-one relationship.
How do I send QLab cues to different channels on a sound desk?
Use multiple device outputs from your audio interface.
Route QLab cue outputs to those device outputs using your audio output patch.
Connect or route those interface outputs to separate desk inputs.
You can then treat each QLab output as its own source at the console.
Why does my QLab audio device say it is missing?
QLab cannot use an output device if macOS no longer makes that device available.
Check that the interface is connected, powered and recognised by the Mac.
Then check your QLab audio output patch.
If the hardware uses its own configuration software, check that as well.
The Most Important QLab Troubleshooting Rule
When QLab has no sound, resist the temptation to start changing things everywhere.
Follow the signal.
Audio file
↓
Audio cue
↓
Cue output
↓
Audio output patch
↓
Device output
↓
Audio interface
↓
Mixing desk
↓
Sound system
Find the last point where you know the signal exists.
Then investigate the next part of the chain.
That is how I would troubleshoot the problem during a theatre production, and it is a far faster approach than randomly changing settings until sound comes back.
More importantly, learning to think this way takes you beyond knowing which buttons to press in QLab.
You start understanding QLab as one part of the complete theatre sound system.
Learn QLab for Theatre
I am developing QLab for Theatre for people who want to learn how QLab is used on real theatre productions.
It will go beyond basic cue programming and cover areas including multi-output audio routing, show-file structure, theatre workflows, templates, programming and live fault finding.
If this guide helped you understand QLab audio routing, that is the next step.
Rather than learning isolated QLab functions, you will learn how those functions fit together when you are building and operating a show.
Useful QLab documentation:
Introduction to Audio in QLab:
https://qlab.app/docs/v5/audio/introduction-to-audio/
Audio Output Patch Editor:
https://qlab.app/docs/v5/audio/audio-output-patch-editor/
Workspace Status Window:
https://qlab.app/docs/v5/tools/workspace-status-window/
QLab Features by Licence Type:
https://qlab.app/docs/v5/general/features/