Tomas Pettersson wrote a small application, that hit the gaming scene like a rock. SFXR is a sound tool to quickly make sound effects to use in any game. At least Tomas is very surprised about the success of this application, because for him it was just a logic step to write that app.


Tomas “DrPetter” Pettersson is a 25 year-old guy from northern Sweden who has been toying with computer programming since the age of twelve. His first real contact with electronic and computerized entertainment was the NES and from there it has progressed through the classic line of various consoles, C64, the Amiga and finally PC. Since 2001 he studies computer science and technology at the Linköping University in Sweden, but most of his spare time he uses to experiment with all kinds of things from sound synthesis to game/utility development, music composing and drawing. Digital Tools asked him some questions on the SFXR tool, the context it appears and on future plans and inspiration.

Hi Tomas. Why did you made this tool?

The main motivation for this specific application was that for several years I had noted a distinct lack of sound in most LD48 games.

What are LD48 games?

LD48 stands for Ludum Dare 48-hour game development competition. It is, as the name implies, a competition where entrants sit down and develop a game within a period of 48 hours. Everything about the game has to be created by one person within the given time limit, so you’re not allowed to use content downloaded off the net or borrowed from friends.

And that is where you SFXR comes into play?

Exactly. In the descriptions and comments of the compo it was indicated that people would have liked sound and the makers had added some if they only knew of a simple way to create them in the first place. For visuals, anyone can at least create *something* using MS Paint, GIMP, or simple procedural/programmed graphics. In contrast, most available sound synthesis tools require some specific knowledge to use at all, and few people seem to know what to look for if they need one.

Sounds are far from irrelevant to the gaming experience though, so it’s unfortunate to neglect them almost by default when you can’t invest the time to research ways of making them. Having a simple program readily available that can give you decent content in a few seconds of playing around would pretty much solve the problem. In my opinion it doesn’t make things unfair either, since the quick-n-dirty sounds are for people who normally wouldn’t have sounds at all, and the more ambitious people will always spend more time to get specific tweaked sounds that stand out as more polished, using my program or not.

Just another reason for making this software is simply the fact, that I’m a sound junkie and had played around with the general idea of a sound effect tool for quite some time.

What was your basic design concept on the SFXR?

There wasn’t much design up-front. I knew that I wanted some central synthesis ‘engine’ that would be capable of generating a wide variety of sounds. So the first thing I did was to put in some simple aspects like a tone generator with selectable waveform and volume envelope control, as well as some simple slide functionality. These are all basic things in sound synthesis so it’s a no-brains way to start. To control the values for testing I just added a simple graphical slider code that I could copy-paste and bind to each parameter.

I started working some 4-5 days before the compo starded and this initial tinkering went on for a day or so, adding more effects to the synth code and putting the corresponding sliders into the interface. At some point I realized two things: First, the sliders worked rather well for controlling the sound and second I wouldn’t have time to make the interface more complex while the compo was about to start within days.

Failing to release it before the competition wasn’t an option, so I just sat down and tried to work what I had into a usable state. I did a pre-release two days before the compo started, to see if there were any major issues that I had to address. People threw a bunch of feature requests at me, most of which I wisely ignored in fear of getting in over my head. The most sensible ones in terms of benefit vs. time to implement were added. And I also put in a few more effects and options that I had pondered with earlier.

What are the expected results or the next step on your tool?

The expected results have already been met as a lot of people did use it for adding sound effects to their LD48 games, which is great.
In terms of the sounds produced by the application I was pleasantly surprised, as both the quality and variety of the output turned out considerably better than I had anticipated. The random button is awesome in its simplicity, I get spooked out every time it spits out a great new effect or even a dead ringer for some old sound that you recognize from a real game. The only ‘intelligence’ about it is that it tries to avoid obvious dumb ranges or combinations of parameters, such as starting at an extremely low frequency and sliding down. I’m very glad that it got implemented, as it was one of those last-minute additions that I hadn’t originally thought about.

For future versions I have a few minor tweaks planned, and I will probably release that as a v1.1 or something. There’s an unlimited range of extensions and redesigns possible, but most of them would complicate the use of it and as such destroy the important simplicity that it has now. One possible approach would be to simply add an optional ‘advanced’ mode where you have more detailed control over things, but maybe that’s better done as a separate application altogether.

At any rate, the source code is available in the SDL port so anyone can set out making their own variation if they have great ideas for it. PoV from the Ludum Dare community already made a VST instrument out of it, which is pretty crazy.

SFXR_5minutes.pngmusagi.pngDetails from SFXR and Musagi

Does that mean, that you are quite satisfied with your results so far?

I had definitely not expected this kind of attention around SFXR. It’s just a little hack designed to fill a small specific need, and I would have been happy if three or four people would end up using it for the compo and nothing else was said about it. I guess the small specific need turned out to be more widespread, that anyone though. Like many of the comments said something like “Finally! I’ve been looking for something like this forever!”.
Hopefully more people will end up using it for their productions and maybe as a springboard into more advanced sound synthesis once they’ve figured out what the various sliders actually do.

It think this is a good place to say something more about the LD48 compo and the Ludumdare Website.

The Ludum Dare 48 compo is open to everyone and we regularly get participants from all over the world, which can sometimes get unfortunate as you easily tend to stay up very late in your timezone interacting with people halfway around the globe. Nevertheless the number of people entering usually ranges from 50 to 200. Normally half of them end up submitting a game before the deadline. Between the competitions there is a smaller crowd of about 10-20 people hanging out in the IRC channel #ludumdare on

There is a somewhat unintentional tradition of improvised hosting in each run of the competition, and some have worked out better than others. Right now there is work underway to secure a solid site that can be reused for all coming compos, and it’s likely to be hosted at The latest run (#10), lives on a WordPress setup at We’ve gathered up quite a lot of content there already, so if it doesn’t end up being the default site for future competitions we will at least have to migrate a lot of the data to whatever system we do end up using.

Something more about yourself. What drives you and what are you working on at the moment?

Like I already said, besides studying computer science my spare time is dedicated to experimenting with all kinds of things from sound synthesis to game/utility development, music composing and drawing. The old 80’s computers, video games and their content inspire me in many ways, with regard to technology, gameplay, sound and graphics. My Winamp playlist is often packed with authentic retro game tunes or contemporary music derived from them and I prefer good old blocky pixel graphics in games, doesn’t matter if new or old.

The main thing that keeps me around if you’re an audiophile is Musagi, a software synthesizer and music composer and sequencer application with a nod towards retro sounds. This is something I’ve long wanted to make, and I finally started it mainly for my brother as he had an urge to learn music composition a few years ago but didn’t like the available tools which often give an intimidating impression of being overly complex. Musagi in its current state might not come across as dead simple. The instrument interfaces are currently rather arcane though, as I settled with a pretty small fixed window size for them and am starting to regret it now. This might have to change in future versions. I also try to stick with an ‘obvious’ single-state interface for everything I add to the program, so that you always have an overview of what’s going on but preferably without cluttering the display too much. The program is in constant development and is currently in need of some more complex and conventional synth instruments. There might be an update coming in the next few months.

My always-outdated homepage has a modest overview of my work. I try to put up things that are somewhat presentable and/or of potential interest to people.
Check it out here:

Thanks for this Interview. We’re really looking forward new tools from you to come. SFXR is at least a very usable tool and a great inspiration, too.

Text and Interview: Martin Wisniowski, December 2007


Tomas Pettersson’s Website

Ludum Dare 48 Game Development Competition



Interview - Date published: December 23, 2007 | 2 Comments

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  1. jikoo said:


    The website of Sfxr is down for long time. So now, you can download it here :

    It’s my website about chipmusic, chiptune, 8bit music…

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