2. Definition

The basis for the modulation effects is usually some kind of a beat.

This usually refers to a special tonal impression, which is created when two vibrations with a difference of only a few Hz in their frequencies resonate simultaneously. The sonic pattern becomes more vivid and fleshed out, when two slightly differing sounds meet each other. We simply need to listen to a single violin playing a piece of music and compare that sound with the one originating from the violins in an orchestra. As mentioned: the sound is the same, but due to the light, unavoidable differences in tuning (and due to human differences of course) a string orchestra will sound distinctly richer (and not only louder!).

If the second signal suffers a slight delay, too, additional phase cancellations are created (determined by the length of the delay, which can be set with a manual regulator on most of the devices) and the overtones are already merrily twirling around each other. The effect can be amplified if a part of the signal is fed back again from the front; feedback controllers can be found on numerous flangers and phasers.