Live sound and the sound system?

Question

Is there a difference between a live sound, whether it be a human voice or a car, and a recorded sound played through loud speakers? More specifically, are there any tangible scientifically distinguishable elements between the two?

Answer 1

Modern audio technology is so good that it would be nearly impossible for a human, or any collection of scientific instruments, to detect the difference. Probably the best way to tell is with spatially diverse sensors. Apply enough technology, and you could probably distinguish between original sound from a point source, and reproduced sound from multiple speakers. The other way would be to analyze sounds outside the human audible spectrum. But that's cheating, since audio systems don't try to cover much beyond the audible.

Answer 2

Any speaker is going to have a limited range of frequencies it produces. Really good speakers cover the entire range that the human ear can pick up, and a little extra just in case. But most real sounds have bits and pieces that go outside our range of hearing, even the human voice.

So, if you analyze the full range of frequencies on a sound, you can generally tell if it cuts off at a certain limit, marking it as a recording. However, your analyzer has to have a broader range than the speakers, so it becomes a sort of arms race between the person faking the sound and the person trying to detect the fake.

If you're doing this for a plot point in a story, you don't really need to worry about the arms race aspect unless the person doing the faking expects to have to fool computer analysis. If they only expect to have to fool the human ear, odds are the speakers won't go much past audible range.