Ringing (signal)

This article is about ringing in electronics and signals generally. For ringing artifacts in signal processing, particularly image processing, see ringing artifacts.

An illustration of overshoot, followed by ringing and settle time.

In electronics, signal processing, and video, ringing is unwanted oscillation of a signal, particularly in the step response (the response to a sudden change in input).klnklnk;lnkl It is also known as hunting. It is closely related to overshoot, generally occurring following overshoot, and thus the terms are at time conflated.

It is also known as ripple, particularly in electricity or in frequency domain response.

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.

Ringing can be due to signal reflection, in which case it may be minimized by impedance matching.

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. In a CRT 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.

Audio

Ringing affects audio equipment in two ways. Audio electronics have the same ringing issues as do all electronic equipment, with the exception that the ringing may be audible. In addition, transducers (ie, microphones and loudspeakers) can also ring. Arguably, mechanical ringing is more of a problem with loudspeakers as the moving masses are larger and less easily damped. Mechanical ringing, unless extreme is difficult to audibly identify as such. It is usually noted as a like of characteristic 'coloration' in the sound and is very hard to describe in words.

An additional effect often heard in sound reproduction is sometimes referred to as ringing, but is in fact a kind of feedback. This is a piercing squeal or screech, caused by loudspeaker output being picked up by one or more microphones and passed through the amplifier and back to the loudspeakers again. Given a particular sound system and a particular room, some frequency will be emphasized, will be the first to 'runaway' in a positive feedback condition, and will cause the screech. A system on the verge of runaway feedback often has a peculiar wavery, ringy quality as it goes almost into and then somewhat away from actual runaway feedback.

Signal processing

Main article: Ringing artifacts

In signal processing, "ringing" may refer to ringing artifacts: spurious signals near sharp transitions. These have a number of causes, and occur for instance in JPEG compression and as pre-echo in some audio compression.

See also

• Microphonics
• Ripple (electrical)
• Impedance matching

External links

• Microphony with older video cameras