Playing Sounds on Collision in Unity

Unity sound engine offers a decent performance for most little projects, but when looking for more advanced audio features, it usually falls short. With this project we aim to mix the power of FMOD Studio with the Unity physics engine.

Keep reading if you want to learn more!

Unity audio engine is good, isn’t it?

For the past month, I’ve been working with a colleague of mine on this idea about making a solid collision sound engine. At first it may seem like there’s not much to do, since Unity already provides its own audio capabilities, and syncing it with the physics engine is an easy task.

The problem is, Unity’s audio engine is not really prepared to handle more advanced projects. As a game’s complexity grows, so does its audio’s. In order to keep a clean, understandable and easy to modify audio project, middleware such are FMOD can come in handy.

The power of FMOD

In FMOD Studio, the base unit is the event, if you want to play a sound, you must create an event and assign the audio file to it. Since the key element are the events, specific files lose importance. This means you could change the entire audio of a game while keeping the same structure.

For example, if you are making a shooter, at some point you’d probably like your gun to play a shoot sound. If using Unity, you’d need to add an Audio Source component to your gun, and then make it play from your code when shooting. That’s an okay reasoning, it’s easy to understand and pretty straightforward.

But if you try to make it more complex, you start to notice some weaknesses. Like if you tried to make slightly different sounds for each bullet, not to make it look so repetitive. You would need, of course, to code it. But how the sound sounds is a problem that should be taken care by the sound designer, so why in hell would you need to code something like that?

If instead you were using FMOD Studio, the programming gets out of the equation, the sound designer can just randomize a parameter every time an event gets played, and apply different effects depending on that. As easy as that.

So what about the project?

If you want to play sounds anytime a collision is detected between two objects, you can use the Unity engine, but if you’ve read the previous paragraphs, you’ll notice why this is not such a great idea.

If your game audio starts growing in complexity, it will get completely out of control, and changing the smallest sound will become a nightmare. This gets specially troublesome when working in a team, because your sound designer would need to mess with the Unity project to do his/her work.

So, you tight up your shoes and get into the FMOD business, how hard can it be? While the FMOD Unity integration can be easily handled, synchronizing and tuning it up correctly with the physics engine can require much more work than one may initially think.

You can use the trigger function that comes with the FMOD Studio Event Emitter, but that won’t get you very far, since you’d still need to code the selection of the event depending on which body the GameObject collides with.

That’s where this project comes into picture, the idea is to provide an extended Unity FMOD integration for those who wanna handle sounds on collision.

How does it work

Let’s take a look at how to setup a simple Collision Sound project, I will not delve into much detail in this post, if you want an in depth guide you can find it here.

We’ve tried to keep the project as clear and straightforward as possible, but if you’ve never worked with FMOD before, you should go learn the basics before trying to use Collision Sound.

The project works [in general terms] as following: from the FMOD side, there’s a project with all the events that will play on different collisions, it will handle everything related to the sound itself; Unity will take care of the logic, you only have to configure the SoundCollider script on the GameObjects you want to behave as such.

I recommend you to download this demo, it will be much easier to understand than just reading about it.

FMOD Setup

In the FMOD Project, there’s a parent folder named SoundMaterials at the root of the project, and each of its events must be assigned to a bank with that same name.

Every subfolder under SoundMaterials represents each different material, and it must have at least one event with the same name as the folder. This is the default event, it will be played when colliding if no other more specific event can be found.

Specific collision interactions can be created by adding one event with the name of one of the materials under the folder of the other material. e.g. “wood/metal”: metal event under the wood folder, it will be played every time wood collides with metal (or vice versa).

Unity Setup

Unity setup is very simple, just import the package, add a FMOD Studio Listener to your camera and start adding SoundCollider events to anything you want to play sounds on collision. Just remember that it must have a valid material name and as well as a Collider[2d] and a RigidBody[2d] (unless the collider is a trigger).


Those are some of the key features of Collision Sound:

  • Generic & specific sound material interactions (different events depending on what collides with what).
  • Built in parameters that auto sync in runtime: velocity, mass and size.
  • Custom parameters, you set your custom FMOD parameters from code for any SoundCollider.


We’ve put up a very simple demo in Unity to show how this project works and how it should be used. Check out the video to see it working, or download the Unity project if you want to test it yourself.

Thank you!

Thank you for reading to the very end, I hope you liked the project. If you didn’t, please let us know why and how would you improve it, it would be of great help!

If you want, you can contribute to the project on Github ; not only with code, but also posting any issue you find or requesting features you reckon would be cool to have.

Thank you for reading me

Hi, I'm Sergio Abreu García and this is my blog, where I mainly talk about technology & software. You can use my RSS feed to easily keep up with my content.

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