why when we hear things at the same exact time twice it sounds like an echo instead of normally just louder

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why when we hear things at the same exact time twice it sounds like an echo instead of normally just louder

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When your brain hears a sound, it’ll process it for a moment and then go, “oh, a sound”. That takes a short but non-zero amount of time.

And during that time, there’s the chance for new sound information to arrive. In which case, the brain can possibly merge that new sound into the existing sound it’s processing. But if the newly-arriving sound reaches you *after* the brain has identified the first sound, then it can’t be merged in. Which seems obvious *after* you’ve been told that.

So if you have two identical sounds (or nearly identical) which arrive more than 20ms apart, you’ll process them as separate sounds. If they’re less than 20ms apart, you’ll hear them as one sound.

And here’s the really useful part: you’ll hear the *direction* of the sound based on the first copy to reach you. The second copy (if arriving within 20ms) adds to the volume of the single sound you hear. Why is that useful? Because you can have a few tiny speakers, one big speaker, and put a small delay on the signal to the big speaker. The tiny speakers control the apparent direction of the sound, and the big speaker provides the oomf. So you get surprisingly loud directional sound out of tiny little speakers.