As you are probably already familiar with, instruments do not produce pure notes, but each note is accompanied by members of what is called the overtone series. This is a major factor in what causes the same note to sound different on different instruments; they all have different relationships with the overtone series. Let’s talk about the oboe’s overtones and why it has such a unique sound.
The Overtone Series
As a brief overview, the overtone series is the pattern of notes that are also sounding above your target note. The note heard is called the fundamental and it is the loudest and most prominent. The next note (or the first overtone) is an octave above, or twice the frequency of the fundamental. The next overtone is a fifth above the last one, and the third overtone is two octaves above the fundamental. The fourth overtone is a fourth above the last (two octaves and a fourth above the fundamental). The sixth is another third up from the last fundamental. The overtones continue from there and continue to get higher and closer together. The higher you go in the overtone series, the more frequencies will appear that are dissonant with the fundamental. This is also the basis for scales and keys as used in Western music: the fourth, fifth, and sixth overtone produce a major chord.
Here is a chart that will be more clear:
The overtones we have been talking about are harmonics, which are the type of overtones that are exact multiples of the fundamental in frequency. There are in-harmonic or dissonant overtones as well that are especially produced by drums for instance, but string and woodwind instruments are designed to produce the harmonic overtones as much as possible.
The Oboe’s Overtones
The oboe produces all of the harmonic series and its unique sound comes from the emphasis the oboe puts on the higher parts of the harmonic series. You can see in the chart below that the clarinet has much heavier “odd numbered” overtones and this alternation of prominent and very soft overtones gives it a hollow sound. The flute’s overtones decrease in intensity very evenly giving the flute a pure sound, and the trumpet has a very prominent second overtone as well as still very strong upper harmonics which give it a brilliant sound. The oboe in comparison to these has the most prominent overtones series as well as the most emphasis on the upper harmonics. These upper harmonics contribute to the oboe’s nasal sound as well as the “density” of sound and how the oboe can cut through a lot of noise so easily. This is also a good visual for why trumpet and oboe pair together so well.
There is a lot more that could be said about this like how playing at different volumes will produce different overtones or how the register you are playing in might affect the overtones produced as well. There are extended techniques that manipulate the overtone series, but you might not have thought much about how even basic playing uses the harmonics produces by the oboe. We will come back to that later!