In electrical circuits, ringing is an unwanted
oscillationof a voltageor current. It happens when an electrical pulse causes the parasitic capacitances and inductancesFact|date=May 2008 in the circuit (i.e. those that are not part of the design, but just by-products of the materials used to construct the circuit) to resonate at their characteristic frequency. Ringing artifacts are also present in square waves; see Gibbs phenomenon.
Ringing is undesirable because it causes extra current to flow, thereby wasting energy and causing extra heating of the components; it can cause unwanted
electromagnetic radiationto be emitted; it can delay arrival at a desired final state (increase settling time); and it may cause unwanted triggering of bistable elements in digital circuits. Ringy communications circuits may suffer falsing.
In video circuits, 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. The electron beam upon changing from dark to light or vice versa instead of changing quickly to the desired intensity and staying there, overshoots and undershoots a few times. 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.
In hearing, ringing is an endaural phenomenon in which a person hears a sound, somewhat like a
pure tone, without any external acoustic stimulation. Ringing in the ears commonly follows exposure to loud noises, and is a sign of damage to the hair cells of the inner ear. Ringing in the ears is a common sort of tinnitus.
Bird ringingis using individually-numbered small metal leg rings placed on birds' legs to track their activity.
Ringing current is the pulsating DC current that powers a telephone bell.
* [http://www.michaeldvd.com.au/Articles/VideoArtefacts/VideoArtefactsMicrophony.html Microphony with older video cameras]
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