I've created a drone that I'd like to use as a spacecraft engine bg, but right now its in mono, and I thought I'd crowd source some favourite methods of "stereoizing". Because the sound is sci-fi in nature, I'm not particularly concerned with realism or colouring the sound (though more realistic methods are welcome too). The two sounds that I'm working with are here, if you want to give them a listen:

[soundcloud]adamaxbey/engine-2[/soundcloud] [soundcloud]adamaxbey/engine-3[/soundcloud]

  • Excellent thread - lots of techniques I wouldn't have thought of but would like to try! Aug 29, 2011 at 20:37
  • Thanks everyone! I'm gonna try some of these and post results.
    – AdamAxbey
    Aug 29, 2011 at 23:30
  • If you feel like scrolling down, I've tried a few of the techniques suggested below. Shaun's, Filipe's, Tim's (though without changing perspective), Chris' and two of Matt's (he suggested grain, so I used GRM)
    – AdamAxbey
    Aug 30, 2011 at 15:24

15 Answers 15


I'll +1 Filipe's comment and build on it. If you really want to cement it by having a tiny amount of the right in the left (and vice versa) do this:

  1. route your intended "right" signal out of the right channel (obviously)
  2. also route it to an aux to feed the left channel
  3. delay the aux anywhere in the 10-30 ms range (to taste, don't go above or below this range)
  4. drop the volume of the aux to suit your taste
  5. repeat for the opposite channel

The 10-30 ms delay and volume shift exploits the way hear. Anything less than 30 ms (sometimes up to 40, depending on the source and the space) that's heard in a different position than the source, we tend to associate as part of the source sound. In other words we still localize it as being in the right, even though we're actually hearing an echo in the left. If it gets higher than 30-40 ms we start to identify it as an echo or reverb hapenning in the left, and no longer localize it as part of the source sound.

This is a great technique to use in combination with what Filipe mentioned, because you actually create a "space" that the left and right channels interact in. Use the delay to change the "size" of the space: longer delay equals larger space, shorter delay equals smaller space. Use the gain of the Aux to control the width of the stereo image: low gain equals wide stereo image, high gain equals narrow.

This also works pretty well for creating a relatively natural reverb between the front and rear speakers for a stereo file in a surround session. Just apply the above between the front and rear speakers per channel, rather than between the left and the right. Within the delay window, we still localize everything as coming from the front, but we get the impression that we're actually in the space. It's a lot less resource intensive than a reverb plug-in if you're running out of DSP and you only need a small and simple "space." It's not always the best solution, but it's a handy trick to have.

Edit: I should have mentioned that it's important to watch for phase cancellation issues using this method. I've got a Dolby DP570 at work that makes it easy to check different fold-down configurations on the fly.

  • @Shaun, i was actually just thinking about trying the aux to the opposite channel haha, i'll have to try it out tonight, thanks! Aug 29, 2011 at 14:43
  • Also, maybe a lowpass in the aux at around 12k or so? Aug 29, 2011 at 14:44
  • Oooh. I've used the delay trick for years with music stuff, but the double-routing idea never occurred to me. Good one!
    – g.a.harry
    Aug 29, 2011 at 15:43
  • @Filipe Chagas - sure. no reason you can't slap an EQ on that aux. i usually go for a wider image when i pull this. at the lower volume, EQ's have less of an effect...but it could be very useful if you're going to keep that aux louder. Aug 29, 2011 at 16:13

For that kind of stuff, i usually just cut the file in half and put the second part on(in?) a adjacent track , cut them both to be the same length and drag them to a stereo track. You have to be careful when the material has rhythmic patterns to it, other than that, its fast and it works.


If its for film I personally would likely do more than just stereo-ize it, depending on the context/location/point of view that you are hearing it from - I'd use Altiverb with real & non-real IRs to spread the drone to L/R and into surrounds.... But it totally depends where you want the sound to appear to be coming from & how present you want the pulse to be... I'd probably use LowEnder to reinforce the pulse of it with low frequencies & LFE....

Also a note: if you are using psychoacoustic techniques and its film, bear in mind you cannot predict where the audience is sitting... a technique based on subtle time offsets between L&R may be completely lost on most of audience, which is why more discrete processing/placement (such as @Filipe Chagas suggests) will work better


I've tried some of the aforementioned processing and uploaded it, file names included the user who suggested the technique. I'll try to process a few more tomorrow. I've also made the original tracks downloadable (at least for a few weeks or so) in case some of you want to mess around with "stereoizing" 'em. [soundcloud]adamaxbey/engine-2-shaun-farley-aux-10db[/soundcloud] [soundcloud]adamaxbey/engine-2-chris-fonte[/soundcloud] [soundcloud]adamaxbey/engine-2-filipe[/soundcloud] [soundcloud]adamaxbey/engine-2-shaun-farley[/soundcloud] [soundcloud]adamaxbey/engine-2-tim70-wet[/soundcloud]

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  • clicking on info will reveal which user's processing technique I've used.
    – AdamAxbey
    Aug 30, 2011 at 1:17

The delay trick is always a great one. I sometimes use a sample delay or time adjuster as opposed to a regular delay.

I'm very fond of duplicating the mono sounding track, panning the two tracks left and right, and then slightly pitch shifting the duplicate. I personally generally prefer pitching down, but pitching up sounds good too.

Plugs like Waves Doubler work great too, really just delays and pitch shifting also.

Sometimes instead of pitch shifting, I'll time stretch the duplicate slightly also. Gives the image an interesting pulling kind of motion.

also, Eq'ing the two sides separately can do the trick.

as can putting a short modulating reverb on each side, preferably with different modulation times to spread out the image further.

Also, at the expense of being a little more forceful with the sound, using a granular process with a fair amount of pan jitter and a fast grain rate can do wonderful things to a mono image. slap a reverb on afterwards to smooth it out, sounds instantly ominous.


Bus the mono track to a stereo channel with a 15 ms delay on the left channel and a 35 ms on the right.


I'm a big fan of SHEPPi, especially for things that aren't going to be up close and personal.

On top of that, stereo delays and choruses can be used to good effect. For Sci-Fi-type sounds, I tend to go to Native Instrument's Kore pack Deep Transformations (I probably have an installer for the free player and the two free upgrades somewhere, now that it's no longer available), though they tend to be incredibly rhythmic by their musical nature.


For me, the easiest way to widen a mono-sounding file is to process it in the Mid/Side domain. Usually I would apply something like this:

  • delay the right channel for several milliseconds
  • add Mid/Side decoder

That's it. Simple yet effective.

You can achieve this by using a chain of plugins or just a single one. I like Fabfilter effects for this purpose. They allow to process Mid and Side channels separately. Also MSED, Sound Delay, Marvel GEQ and Overtone GEQ by Voxengo are very useful. And free.


I did a blog post on this a while back. Basically anything that can be done to alter one channel without making it sound like a completely different sound. In PT I usually duplicate my mono region onto two mono tracks, alter one or both in various ways - delay, pitch shift, EQ, flip front and back halfs, subtle distortion - then drag both onto a stereo track and consolidate. I also like subtle flanger settings for turning mono to stereo or making stereo even wider.


I tend to find that quite a few 'stereoizer' plugins create rather unpleasantly phasey-sounding results but one plugin I've tried that I did like was Voxengo Stereo Touch.


If it's sci-fi-y and doesn't really matter if it's realistic, paste the mono file into a blank stereo file in a 2-track editor, and then just reverse one side.

Not realistic by any means, but very wide. Particularly if it's just a 'drone' sound and 'direction of movement' is not obvious.



While mixing I try to use Hardware like the Lake People ARTI ST-F10 or the Orban 245. Very convenient way to generate some sort of stereo. Though you need to take care for coloration of your audio. But sometimes it's almost a life saver. At least for the Lake People I can say that it is possible to make IRs from it and use them in Altiverb. Though I'm not sure this gives a full and precise reproduction of the process and I'm not sure about the Orban either. (forgot which principle it is working on)

I always wondered why there are so few plug-ins around offering a similar service.

When I'm editing I often prefer Filipe's approach (where possible) or go with Tim in trying to create a natural sounding result. But I've also had reasonable results with using M/S techniques for old ambiences that we needed in stereo. But other than Denis suggested, I'd use a short reverb or echo for the side channel. The program needs to be carefully chosen in order to not color the main signal in an unwanted way. By working from there I've even manually upmixed mono music into 5.1 before I had stuff like the Unwrap available. It just takes a lot more time - but can also be fun!

But at all times (for film) keep an eye on your phase relation. depending on the sound and its use you might not want to get too experimental with this.


If the room I'm in is quite enough and the right combination of live and dead (and I can spare the time) I find it to be kind of fun to play the sound out of one speaker and throw the Crown SASS-P up a few feet away from the speaker and record it. After a little experimentation with distance, orientation and volume the results can be pretty gratifying.


i use iZotope Ozone 4


I was searching through my library for some school bus sounds and ran into a L and R version and then stereo. For one reason or another, I previewed the L version and thought whoops so I switched to the stereo version. I noticed that phasing helped me determine space and depth or stereo field.

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