As we continue our series on music theory basics, we’re looking at octaves. When we looked at the notes on the treble and bass clefs, you probably noticed that they are named after the first 7 letters in the Latin/Roman alphabet: A B C D E F G.

After G, it loops right back to A. This means that from any given letter to itself again is a movement of eight notes. Because of that, we call the distance from a letter (note) to that same letter (note) an octave, which can go either up or down in pitch. Many musicians can hear an octave and know that the pitches are different, but somehow the note is the same. Why is that?

Any note has a frequency that our ear converts into pitch. Middle C has a frequency of 261.63Hz. Octaves stand out so well to our ear because an octave down is half the frequency of the original note and an octave up is double the frequency of the original note. So from Middle C to the next C up, we jump from 261.63Hz to 523.25Hz.

The halving or doubling with octaves can be visualized using organ pipes. In a pipe organ, pitch is determined by the length of the open pipe. In this case, the length is inversely proportional to the frequency — meaning that the longer the pipe is, the lower the pitch. So if an eight-foot pipe is a C, then a 16-foot pipe and a four-foot pipe would also be a C but a different octave.

The idea of the octave is incredibly important for music theory, because it gives us the framework for dividing sounds and repeating patterns. If we understand what’s happening inside of an octave, we can apply that knowledge to the rest of the audible spectrum.

Written by Matthew Wesley, chair of the CLEF Life committee and volunteer choir member and cantor at Epiphany of the Lord Catholic Church in Oklahoma City.

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