The overtone series is the basis of tonal music. The order of pitches in the series has established the progression of Western Music over the last 300 years. Among its uses are a blueprint for effective chord voicings and an understanding of chord tones and tensions.
What is an Overtone
In order to understand the overtone series (also referred to as the Harmonic Series) you must first understand what an overtone is. I'll try to explain it without getting too deep into the science of acoustics.
As you probably know, when you play a pitch you are hearing a specific frequency. For example, most musicians tune to an A that vibrates at 440 Hz.
What you may not realize is that on top of that fundamental pitch of A 440 you are also hearing a series of overtones, other pitches that are mathematically related to your fundamental pitch. So when you hear A 440, you are also hearing the overtone at a ratio of 1:2, or 880 Hz. And you're hearing 1:4, 1760 Hz, etc.
Because the fundamental pitch is so prominent, these overtones are usually felt more than they are heard.
The Overtone Series
Here is the overtone series based on the fundamental pitch of C. Each successive pitch is weaker in strength and importance than the one before it.
The series begins with an octave, followed by a fifth and then back to the next octave.
Next we have the major third, the next fifth, and then the b7.
Finally we have the next octave up (notice how after a pitch class has been introduced once, it becomes used every octave), the 9th, major 3rd, #11, fifth, 13, b7, major 7, and finally another octave.
What To Notice
There are a few things that are significant about this series of notes. The first is that as we go higher up the series, the notes get closer together. This makes sense if you think about it. If you have a 12 inch ruler and you cut it in half, the ends are closer together. Cut it in half and they're closer together again. Nothing too astonishing.
Next thing to notice is that the octave and fifth appear earliest and most regularly, followed by the 3rd and 7th, then followed by tensions 9, #11 and 13. The higher up the series we go, the more harmonically dense it is and more complex it sounds.
The Overtone Series Throughout History
The overtone series can actually be used to trace the progression of harmonic development through Western music. As George Frederick McKay points out in The Technique of Modern Harmony, different eras throughout musical history became more accepting of higher reaching chord tones in conjunction with the overtone series.
Octaves and 5ths are primal intervals, natural to ancient music. The use of the third became prominent in the Renaissance and with composers such as Palestrina in the 1500s. Bach and his contemporaries began to exploit the 7th in the 16th and 17th centuries. The 9th didn't become an important chord tone until the time of Wagner in the mid 19th Century, and the extended tones of #11 and 13th weren't commonly accepted until the music of early 20th century composers like Debussy and Stravinsky.
Where To Go From Here
This tutorial is just a quick tip to make you familiar with the overtone series and get you to begin thinking about its implications. In future tutorials we'll discuss how you can use this knowledge to your advantage when voicing chords and adding extra color to your harmony with tensions.