Another common term for a signal
processsor is an effects unit or effects
device, sometimes abbreviated EFX..
Many signal processors are used
primarily for special effects, such as
the flangers and distortion generators
(fuzz boxes) used by electric guitarists.
Other signal processors are used to
subtly shape the overall sound balance
(equalizers), to control the perceived
spaciousness of the sound or add
perspective (reverb and delay) or to
level the wide volume variations in a
program (compressors) in such a way
that no special effect is perceived.
These same devices, when used with
more extreme settings, will produce
special effects. We prefer the term
signal processor because it covers the
device in all cases, whether used for
mild enhancement or extreme special
effects.