In the field of electronics, the term modulation refers to various ways of combining two signals, usually a fixed-frequency carrier signal and a variable message signal, enabling a communication or audio signal to be transmitted efficiently. This concept is central to radio and TV broadcasting, telephone services and internet communication. Many different types of modulation are used, although most are some form of either amplitude or frequency modulation. Even a brief discussion of these processes would quickly get very technical indeed for now its enough to know that they exist!
In the realm of audio effects, the term is used rather more loosely to describe a number of effects which are produced by applying one of these processes to an audio signal in order to achieve a particular sound. Well concentrate here on the sounds produced, but understanding a few technicalities can help to make things clearer.
Popular modulation effects include chorus, flanging, phasing and tremolo. Todays musicians routinely reach for effects pedals, rack units or plug-ins to achieve sounds which were originally produced by mechanical means, whether by using dedicated hardware or tricks of the trade to coax unusual sounds out of ordinary studio and stage equipment.
Lets take a closer look at both the origins of some of these sounds, and their contemporary versions.