MadSci Network: Physics

Re: What is the scientific difference between music and noise?

Date: Sat Feb 10 00:14:39 2001
Posted By: Justin Miller, Undergraduate, computer science, Geneva College
Area of science: Physics
ID: 981258952.Ph

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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