Ring modulation is accomplished by
multiplying together two audio signals. The resultant
waveform contains
frequency sidebands which are the sum and difference of the frequencies in the
carrier and the
modulator.
A
simple ring modulator is
easy to
build, and is actually a
voltage controlled amplifier in which the
modulation occurs at
audio frequencies.
Guitar tremolo pedals are actually ring modulators with a
sub-audio frequency modulator