|MadSci Network: Physics|
That depends on what you're talking about when you say "music." If by music you mean most typical music that you'd hear every day, then it's a slightly difficult question to answer. Regular Western music since sometime around 1750 has been based on what amounts to be a complicated set of wave frequencies that's been standardized. The A above middle C is a wave at 440 Hz. If you double the frequency to 880 Hz, you get the A an octave above that; halve the frequency to 220 Hz, and you get the A an octave below that. Okay, so I know that didn't help at all. Trust me, I'm getting there. Each half step (like from F to F-sharp) is separated by the twelfth root of 2. If the A is 440 Hz, the B-flat right above it is at 440 * 1.05946 = 466.164 Hz. Still not much help, right? Here's where it gets interesting, if you're a music person like me. There's what's known as the overtone scale that gives each instrument its sound. If an instrument gave off a perfect 440 Hz wave, it would have a very dry sound, and probably nobody would want to play it. When you play a note on an instrument, it actually mixes the wavelength you hear with half the wavelength, 1/3 the wavelength, 1/4 the wavelength, 1/5 the wavelength, and so on. The strenghts of those other wavelengths is what gives the instrument its sound. Also, if you drew a picture of those wavelengths, you see they all have their crests and troughs in the same place, and if they were drawn on a regular x-y axis, they'd all cross the x-axis at the same points. Now, how this differs from "noise": Noise mixes wavelengths that aren't 1, 1/2, 1/3, 1/4, etc. For instance, a siren is usually made up of a load of different wavelengths that might be 1, 1/1.1, 1/1.2, etc. Therefore, it has an "ugly" sound instead of a "nice" sound. I mentioned a possibility of two answers at the top of the post. Here's the other one: If by music you mean any music, then the answer is "not much." In the 20th century, composers have done all manner of things in the name of innovation, such as putting objects between the strings of a piano, or dragging metal chairs across a concrete floor during a performance. Yet, this is still music. The most general definition of music that separates it from simple noise is that music is some organization of any sound and any silence. The key here is "organization." A busy city street with beeping car horns is not music, but if a car horn beeps in the middle of John Cage's "4'33"" then it *is* music, because that composition is just Cage sitting at a piano, and anything that makes a sound during the 4 minutes and 33 seconds is considered a part of the composition. It's a blurry line, to say the very least. But that's the best answer I can give you.
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