Not music nerds, obviously.

I don’t know anything about music. I know there are letters but sometimes the letters have squiggles; I know an octave doubles in pitch; I know you can write a pop song with only four chords. That’s about it.

The rest has always seemed completely, utterly arbitrary. Why do we have twelve notes, but represent them with only seven letters? Where did the key signatures come from? Why is every Wikipedia article on this impossible to read without first having read all the others?

A few days ago, some of it finally clicked. I feel like an idiot for not getting it earlier, but I suppose it doesn’t help that everyone explains music using, well, musical notation, which doesn’t make any sense if you don’t know why it’s like that in the first place.

Here is what I gathered, from the perspective of someone whose only music class was learning to play four notes on a recorder in second grade. I stress that I don’t know anything about music and this post is terrible. If you you so much as know how to whistle, please don’t read this you will laugh at me.

Music is a kind of sound. Sound is a pressure wave.

Imagine what happens when you beat a drum. The drumhead is elastic, so when you hit it, it deforms inwards, then rebounds outwards, then back inwards, and so on until it runs out of energy. If you watched a point in the center of the drumhead, its movement would look a lot like what you get when you hold a slinky by the top and let the bottom go.

When the drumhead rebounds outwards, it pushes air out of the way. That air pushes more air out of the way, which pushes more air out of the way, creating a 3D ripple leading away from the drum. Meanwhile, the drumhead has rebounded back inwards, leaving a vacuum which nearby air rushes to fill… which leaves another vacuum, and so on. The result is that any given air molecule is (roughly) drifting back and forth from its original position, just like the drumhead or the slinky.

Eventually this pressure wave reaches your eardrum, which vibrates in exactly the same way as the drumhead, and you interpret this as music. Or perhaps as noise, depending on your taste.

I would love to provide an illustration of this, but the trouble is that it would look like ripples on a pond, where the wave goes upwards. Sound happens in three dimensions, the movement is directed towards/away from the source, and I think that’s a pretty important distinction.

Instead, let’s jump straight to the graphs. Here’s a sine wave.

It doesn’t matter what a sine wave is; it just happens to be a common wave that’s easy to make a graph of.

In graphs like this, time starts at zero and increases to the right, and the wave shows how much the air (or your eardrum, or whatever medium) has moved from its original position. Complete silence would be a straight line at zero, all the way across.

All sound you ever hear is a graph like this; nothing more. If you open up a song in Audacity and zoom in enough, you’ll see a wave. It’ll probably be a bit more complicated, but it’s still a wave.

Waves are defined by a couple of things: frequency, amplitude, and shape. The particular sound you hear — the thing that distinguishes a guitar from a violin — is the shape of the wave, which musicians call timbre.

A sine wave sounds something like this:

Amplitude is the distance between the lowest and highest points of the wave. Or, depending on who you ask, it might be half that — the distance between the highest point and zero. For sound, amplitude determines the volume of the sound you hear. This seems pretty reasonable, since in physical terms, amplitude is the furthest distance the medium moves. If you tap a drum lightly, it only moves very slightly, and the sound is quiet. If you wail on a drum, it moves quite a bit, and the sound is much louder.

Frequency is, quite literally, how frequent the wave is. If each wave is very skinny, then waves are more frequent, i.e. they have a higher frequency. If each wave is fairly wide, then waves are less frequent, and they have a lower frequency. Musicians refer to frequency as pitch. Non-musicians would probably just call it a note or tone, which musicians would scoff at, but what do they know anyway.

Frequency is measured in Hz (Hertz), which is a funny way of spelling “per second”. If it takes half a second to get from one point on a wave back to the same point on the next wave, that’s 2 Hz, because there are two waves per second. The sound above has a frequency of 440 Hz. (The graph, of course, does not; it’s a completely unchanged sine wave generated by wxMaxima, so its frequency is 1/τ = 1/(2π).)