Tones, overtones, harmonics, and partials
The base, or core, frequency of a sound is known as its fundamental tone.
The waveforms of all sounds, apart from a basic sine wave, consist of the fundamental tone and many other tones of different frequencies.
Non-fundamental tones that are whole-number multiples of the fundamental tone are known as overtones or harmonics. A tone with a frequency that is a fraction of the fundamental tone is referred to as a subharmonic.
The fundamental tone is referred to as the first harmonic. This is generally louder than the other harmonics.
A tone played at twice the frequency of the first harmonic is called the second harmonic.
A tone played at four times the frequency of the first harmonic is called the fourth harmonic, and so on.
Each of these harmonics has a timbral quality that is different from that of the fundamental tone. In general, harmonics that can be multiplied or divided by a whole number, such as octaves, odd-numbered or even-numbered harmonics, and so on, sound more “musical.”
Tones that cannot be multiplied or divided by a whole number are known as inharmonic overtones, or partial tones. When you combine a number of these inharmonic overtones, it tends to sound “noisy.”
Non-fundamental tones that are multiplied by fractional amounts—not whole numbers—are called partials.