Ringing (signal)

Often ringing is undesirable, but not always, as in the case of resonant inductive coupling.

[3] In a cathode-ray tube (CRT) video circuit, electrical ringing causes closely spaced repeated ghosts of a vertical or diagonal edge where dark changes to light or vice versa, going from left to right, whereby the electron beam's intensity overshoots and undershoots the desired intensity there a few times instead of settling quickly.

This bouncing could occur anywhere in the electronics or cabling and is often caused by or accentuated by a too high setting of the sharpness control.

Mechanical ringing is more of a problem with loudspeakers as the moving masses are larger and less easily damped, but unless extreme they are difficult to audibly identify.

Signals constructed as only a partial (not infinite) Fourier series of a function containing discontinuities (e.g. when applying a brickwall lowpass filter to a square wave) create a ringing error called the Gibbs phenomenon before and after each discontinuity.