We could use this as a graphical representation of a single note played on the clarinet. Let’s say this is a mid-range note, played with its ordinary fingering, at a moderate loudness. It’s a quarter note in a moderate tempo, lasting about a second.

If you know anything about graphs, you know that they represent the input and output of a function: they visualize *something* in terms of *something else*. So it would be useful to ask: what are these somethings in the case of this graph?

The X (horizontal) axis is easy: it represents units of time. The curve on the graph is actually a series of points, and each point represents the value of Y (the vertical axis, or the function’s output) at time X. You can imagine a vertical cursor line traversing our X axis from left to right, showing the value of Y at each successive now-time. Continue reading