FMOD: Audio Occlusion / Mixer States

Lately I’ve been researching into the subject of audio occlusion, something that we take for granted pretty much all the time in the real world. In ‘DATA Labs’ there were a few instances in which I noticed issues with this, in particular with the sound of props from other rooms being clearly audible in adjacent rooms, even with walls in between – not very realistic!

I know there are a few ways to go about this, an especially easy option is to use Unreal Engine’s built in audio occlusion features, but in this instance I chose to use Snapshots in FMOD to achieve a similar result. I’m going to develop these over time but for now here is a quick run down of what I’ve done so far.

Hopefully you’ll be able to hear the effect of this above –  as I move between different rooms the balance of levels subtly changes – in the break room for example the coffee machine sound replaces that of the main hum and air conditioning of the office environment. In the rear office, a similar snapshot ducks the levels from the main office creating a more foreboding and eerie atmosphere.

Wireframe Topdown.png
There are 6 main areas of the level so far, however only 5 are accessible.

Above you can see a top down of the level showing the main rooms / areas. Each of these has a mixer state associated with it, or in FMOD speak – a ‘Snapshot’. Each snapshot can control pretty much whatever you want, however in this case I’m using them to control levels of certain props, reverbs and low pass filters.

Break Room Snapshot.PNG
‘Break Room’ mixer snapshot

The picture above shows the snapshot for the break room – the controls that are visible are included in the snapshot, and as you can see the level of the computer group to the left is fairly low, the environment group has also been lowered a little but the rest left untouched (dotted lines). I also added a low-pass filter to ease off the higher frequencies from the sounds of these groups, much in the way that the built in occlusion works in Unreal. I then simply created a trigger volume to trigger this event when you enter the break room.

Break Room.PNG
In the break room – the highlighted box is the trigger volume used to activate the associated snapshot in FMOD.

Another thing that I find helps with snapshots is allowing them to fade in and out using the built in intensity parameter. This helps to create smooth changes between mix levels that might otherwise  ruin the immersion for the player.

Break Room Snapshot Intensity.PNG
I added a AHDSR to the intensity parameter in FMOD giving a gentle 1.8 second fade in and out on the snapshot.

I’ll be continuing to develop this system over time, and I’ll probably look at the built in system in Unreal as well which I feel might offer some benefits in this area. If anyone has any tips or suggestions for audio occlusion using FMOD I’d love to hear them!

2 thoughts on “FMOD: Audio Occlusion / Mixer States

  1. Hey awesome article! I have attempted to do something similar using FMOD snapshots and Unreal Engine, however in a much more simplified manner. Using only two different snapshots, one for inside a cave and the other for inside a temple. Is there any chance you could clarify how you setup the blueprints within UE4 trigger the snapshots.
    Cheers Jack.


    1. hi Jack! Thanks for having a read – glad you enjoyed the post! I used trigger volumes inside UE4 – mapped to the spaces I wanted the snapshots to work in (in this case each of the rooms). I then used the level blueprint to create overlap events for these volumes that in turn triggered the FMOD Snapshots. It’s important to use trigger volumes and not box triggers as these act differently with FMOD audio component I think. Feel free to drop me an e-mail if you want to chat about it or go into more detail!


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