In preparation for the next Ludum Dare, I’ve playing around with Unity for the past few months and there’s something I’d like to share with other aspiring game developers.

My previous Ludum Dare games where created in Flash, and while I was somewhat happy with my coding effort, the games didn’t have any audio. I decided to make things different next time, and have some simple audio feedback on whatever I built.

To get myself acclimated with the language, I decided to port Thomas Vian’s as3sfxr to Unity. What’s as3sfxr, you ask?

This short video from Flash on the Beach 2010 has a great explanation. In a nutshell, however, sfxr is an engine for dynamic generation of game-like audio effects. Thomas ported Tomas Pettersson’s original sfxr to ActionScript, creating a nice API for dynamic audio generation. This API was the basis for usfxr – and really, much of the code in usfxr is a direct translation of as3sfxr, albeit in a more C#-friendly, Unity-happy way.

In practice, what does usfxr do, though? It allows you to publish a game with no static audio assets (all effects are defined by a parameter string), and to generate small variations of the same audio in real time, thus making the audio playback a bit more colorful.

Code for a normal audio effect looks like this:

SfxrSynth synth = new SfxrSynth();

While “mutated” versions of the audio can be played like so:


The library is a pure code port, with no GUI whatsoever (you can generate audio strings in as3sfxr‘s GUI, copy it, come back to your C# code, and paste the string). Other than that, the biggest difference is that audio data is (almost) always generated on a separate thread, so the need for pre-emptive caching is diminished.

I have an example of usfxr in action in a (terrible-looking) Shmup example (requires Unity web player):

usfxr SpaceGame example

The full code is available on GitHub. I’ll probably fix a few more things – mainly write proper documentation, add a different sample, and maybe make it faster – but overall it’s working. And obviously, I’ll be using it on Ludum Dare this weekend.

Some input would be welcomed, of course – I’m not a experienced Unity developer.

This post is a shortened version of something I’ve originally published on my own website.

4 Responses to “Introducing usfxr: generate audio effects dynamically inside Unity games”

  1. jonbro says:

    whoa, this is cool, thanks for doing this! I wish just wishing for something like this, using cfxr on my computer is a bit slow, and the workflow of copying things into unity isn’t the fastest.

  2. rylgh says:

    Thanks so much for this!
    as3sfxr keeps giving me errors so I made an edit to cfxr to make it paste sound data in the format that usfxr wants. Not sure if anyone else would be interested in that but if so I can upload it somewhere.

    • zeh says:

      If you publish it anywhere, let me know through email (zeh at and I’ll add to the page’s readme (or just do an edit and a pull request). In theory any sfxr-like string should work, so there’s a bunch of variants that can be used. I think bxfr works too, but I think the author did some changes/additions to the parameters (I’m not sure).

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