How to create explosion sound effects in audacity

So I find myself having to replace a few sound effects in a game I’m working on due to license considerations. (Fedora wants Creative Commons Attribution Share-alike 3.0, and the samples I was using are Creative Commons Sampling Plus 1.0, which is apparently too restrictive.) Some things, I can record myself, and in fact many of the sound effects I used I recorded myself to begin with, and for those, since I’m the sole copyright holder, it’s easy — just change the license.

But, explosions… not exactly something I can record — instead of “Two Turntables and a Microphone”, I’d have to have Two sticks of Dynamite and a Microphone. Not going to happen. Thought about trying to record firecrackers, trying to make explosion noises with my mouth, trying to hack something together with some loud slapstick bang plus crinkling up plastic… nothing was working.

Then, I remembered I used to make explosion noises on my old ti99/4a computer, ages and ages ago. That thing had a noise generator that could generate several “types” of noise, and a sort of “8-bitty” explosion noise could be made by starting up one of the noise generators, then lowering the volume over time to fade it out. Wasn’t great, but it did more or less sound like an explosion.

So that got me thinking about synthesizing explosion noises from raw data. At first I was thinking I’d have to write a program, to generate random numbers, cram them into a sample array, process them by algorithmic means, then save out a .wav file, and repeat this process, tweaking the algorithms each time, until I got some sort of explosion-y noise out of it.

Then I thought, hey, what if I get some white noise sample, read it into audacity, and start messing with it. First I thought, “no problem, I’ll just record my TV tuned to non existent channel. Well, hmm, my TV mutes when it gets no decent audio signal. Then I thought, hey, I’m being stupid, I can just find some white noise samples on the internet. And so I did, and started messing with that in audacity, albeit with some nagging copyright concerns. (The idea of someone copyrighting a particular sample of white noise is insane, but… still.) Then, I noticed Audacity contains a white noise generator. Tossed out my internet found sample.

So, to get down to it, how to create an explosion sound in audacity from nothing at all.

1) Generate a bit of white noise, a second or two’s worth.

2) Select the whole sample, and apply the “fade out” effect to it.

3) Duplicate this faded-out white noise, and apply the “change speed” effect. Make it slower. Repeat step three a number of times, making faster and slower copies. What’s happening here is the faster copies get raised in pitch, and made shorter, and crammed over on the left hand side (first part) of the sound, and the slower copies get made lower in pitch, and longer, and so the left hand side of the sound gets loaded with high frequencies, and the right hand gets loaded with lower frequences. Make an explosion noise with your mouth, and pay attention to what you do, and you’ll see that it starts out with high frequency noise that kind of fades to lower frequencies.

4) Depending how much “pop” you want the explosion noise to have, whether you want it to sound like a handgun, or like a volcano, you may need to front load the sound with a lot of high frequencies, and watch the length of the tail — for a handgun, it shouldn’t get too long, for a volcano, it probably needs to be several seconds.

5) Periodically select all your sounds, and “Mix and Render”, which will reduce them all down to one sound.

6) You can manually get a kind of low granularity “reverb” by duplicating the sound, shifting it over slightly to the right by inserting a bit of silence, applying negative amplification to get it down in the mix. Repeat this six or eight times, playing around with the amount of negative amplifcation, the delay of silence inserted. You may also want to knock down the attack of some of the echoes by judicious use of the “fade in” effect.

7) Try applying the “phaser” effect, it might do some good.

8) Try using EQ, boosting the bass, boosting some of the higher frequencies 3k and above, dropping some of the mids. Try the “bass boost” function of audacity. (Nice thing, you can “undo” if you don’t like how it works out.

You kind of have to play around a bit to figure out how to get a decent sound, and I say “decent”, but it won’t be as good as a real, well-recorded explosion. But, for most people, me included, recording a real explosion is simply not an option.

Update, Apr 8: You can hear some examples here, at freesound.

Update Apr 13:
I made a video tutorial…

~ by scaryreasoner on April 6, 2008.

17 Responses to “How to create explosion sound effects in audacity”

  1. [...] explosion sound effects in audacity I noticed a lot of people hitting my previous entry about how to make explosion noises in audacity via various google searches, and so it occurred to me to make a video, which I think explains it a [...]

  2. nice work mate, will be using your technique for my college final major project :D.

    Thanks for putting this up! was losing sleep over how to get a more realistic sound than going “PKSHAAAW” into the mic

  3. nice work mate, will be using your technique for my college final major project :D.

    Thanks for putting this up! was losing sleep over how to get a more realistic sound than going “PKSHAAAW” into the mic

  4. Super tutorial! (I can’t believe I say such a thing about a video recording of a monitor! :) ) I wish audacity had a macro recording function, it would be so nice to have the source code of start-from-zero sounds.

  5. The topic of sounds just came up on FGD again and I of course had to think of this tutorial.

    So I want to give you an encouragement for doing more sound tutorials – you don’t have a hand for recording nice screen vids, but you do have a hand for making sounds :D

  6. Cool site, love the info.

  7. a similar aproach, make several reverb clips with different frequency cuts and attenuations. cut out the base white noise, and stack the reverb segments (this will provide a smoother frequency fade out), maybe ad a little bit of pitch decay during intermediate steps. of course you could always start with more complex peices then white noise, using a synth…this makes it easier to emulating underdamped SHO’s (used to modulate such noise).

    great tutorial, interesting method A+

  8. It is very good I did it and it was good

  9. I might have done it wrong, but it didn’t end up sounding like an explosion. With some extreme phaser effect additons on 70% feedback I managed to get a nice sci-fi energy generator loop though.

  10. I kept messing around with it and found a way to get a decent explosion.

    First record a loud noise-maker type firework (air bomb, thunder bomb 4000, etc) Duplicate it at least 3 times and shift the speed, 1 faster and 2 slower. Select the explosion trail, (not the loud concussion sound), make at least 4 copies, apply random speed values and shift their positions around a bit. Next do the above tutorial but with brown noise, and about half the amount of tracks, also amplify the noise by a negative value and shift positions a bit.

    Mix and render, then apply a touch of bass boost. Play around with it a bit and you can get some interesting (and loud) explosions.

  11. Awesome tutorial great way to learn the audacity interface and options

  12. How do you select all of duplicated and mix and render?

  13. Thank-you :)

  14. Thank you very much, this help a lot on a new 8-Bit game I’m making!

  15. [...] Also, as for sound effects, I have a couple of gun shot sounds, walking footsteps, an explosion, not sure what else to add. If you are having trouble making some explosion sounds, you may want to check this out:  http://scaryreasoner.wordpress.com/2008/04/06/how-to-create-explosion-sound-effects-in-audacity/ [...]

  16. Great article. I love it

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