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Opposite Audio Question? Answered


Well, I have some sound clips and I want to be able to generate the EXACT OPPOSITE SOUND. Therefore, when I play the clip with the normal clip, they should cancel out.... This probably sounds crazy to try, but its just a little project I'm working on.... Does anyone know a good program that can do this?




Best Answer 7 years ago

It's not crazy to try at all; you're generating 180-degree phase shifts (different shift for each frequency). If you play the two together, you'll get silence (wave cancellation).

You might try the more complex experiment of writing out the two streams to left and right stereo channels. What should happen (and it'll be really cool if you try it) is that when you sit at the sweet spot between the speakers you get silence, but if you move to one side or the other, you'll start to hear the closer speaker start to increase in volume. I'm not sure whether the ear is sensitive enough for that to work (which is what makes it an experiment :-).

Besides just doing phase inversion, you might look up time-reversed sound. The idea is that sound (or light) gets distorted as it passes through scattering media, but if you project the time-reversed signal back through the same medium, those distortions reverse and you hear the "perfect" orginal signal. This doesn't apply to absorption, of course.


You can invert a sound using audacity (the effect is called invert)... this produces a phase shift of 180 degrees. Dolby Surround basically uses this method to encode/decode the Surround channel to/from Left and Right channels. I did this as a communications project... basically you add the surround channel to Left and subtract (+180 degree phase) from the Right... then when you add the Left to the inverted Right channels you get twice the surround and basically no L&R or at least they become less.

Simplest is to hook up a second speaker connected backward.

Of course these will only cancel out at points that are equidistant from both sound sources. In between, you will get "comb filtering" effects where some frequencies cancel and some reinforce, and the sound changes (usually unpleasantly) as you walk through the space.

Download "audacity". It's free and I believe it will do what you want when you load the clip then select it and pick effects from the menu. Then click on invert.

Well, that's exactly what it does. It's a weird effect if you play both of them at once. Total silence.