The Harmonic Series In order to understand what we are doing when we use an equaliser, we first need to understand how a sound is made up. Most musical instruments produce a tone through exciting a complex series of vibrations in a string or a pipe. These vibrations can be rationalised into a series of more simple modes of vibration.
The Harmonic Series The simplest mode of vibration produces a pure tone, this is known as a sine wave. A perfectly pure tone is not a naturally occurring thing, although it can be generated electronically. From an analysis point of view a sine wave is very useful.
Timbre When we play a note on a musical instrument, different levels of partials and overtones are produced. Stringed instruments generally produce all the harmonics in the series at varying levels, whereas instruments which work on the principles of a closed or open pipe will omit certain partials.
Types of Equalisers An Equaliser works by adjusting the balance of the partials and overtones in a sound. This alters the tone of an instrument. The two most common types of equaliser you will come across are: Parametric; Graphic.