change ringing

Traditional English art of ringing tower or hand bells in a succession of different orders. Groups of swinging bells in English church towers date from the 10th century. Control of bell ringing was much enhanced with the invention of the bell wheel in the 14th century; further improvements in bearings and fittings allowed the bells to swing at the same speed and led to recognizably modern change ringing by the 17th century. A “ring” (set) of 6 bells can be tolled in 720 different “changes” (orders); 8 bells allow 40,320 different changes, and 10 bells allow more than 3,000,000. In practice, only a selection of the possible changes is rung, derived by a “method” (a shuffling algorithm), usually involving switching pairs of bells in a certain order (e.g., 123456 becomes 214365, which can then become 241635, etc.). “Rounds”—all the bells in order from highest to lowest—is rung before and after a method is completed.

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Electricity

In electrical circuits, ringing is an unwanted oscillation of a voltage or current. It happens when an electrical pulse causes the parasitic capacitances and inductances 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 radiation to 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.

Video

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.

Medicine

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.

Ornithology

Bird ringing is using individually-numbered small metal leg rings placed on birds' legs to track their activity.

Telephony

Ringing current is the pulsating DC current that powers a telephone bell.

External links

• Microphony with older video cameras