What is "jitter"

"to move agitatedly," 1931, American English; see jitters. Related: Jittered; jittering.

Etymology 1 n. 1 A nervous action; a tic. 2 (context chiefly in the plural often with "the" English) A state of nervousness. vb. (context intransitive English) To be nervous. Etymology 2

n. (context computing English) A program or routine that performs jitting.

n. small rapid variations in a waveform resulting from fluctuations in the voltage supply or mechanical vibrations or other sources

In electronics and telecommunications, jitter is the deviation from true periodicity of a presumed periodic signal, often in relation to a reference clock source. In clock recovery applications it is called timing jitter. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of periodic signals. Jitter is a significant, and usually undesired, factor in the design of almost all communications links.

Jitter can be quantified in the same terms as all time-varying signals, e.g., root mean square (RMS), or peak-to-peak displacement. Also like other time-varying signals, jitter can be expressed in terms of spectral density.

Jitter period is the interval between two times of maximum effect (or minimum effect) of a signal characteristic that varies regularly with time. Jitter frequency, the more commonly quoted figure, is its inverse. ITU-T G.810 classifies jitter frequencies below 10 Hz as wander and frequencies at or above 10 Hz as jitter.

Jitter may be caused by electromagnetic interference and crosstalk with carriers of other signals. Jitter can cause a display monitor to flicker, affect the performance of processors in personal computers, introduce clicks or other undesired effects in audio signals, and cause loss of transmitted data between network devices. The amount of tolerable jitter depends on the affected application.

Jitter may refer to:

• Shaking, such as shivering, myoclonus, tremors, or a possible symptom of panic attacks, or of triggering in post-traumatic stress disorder

In electronics and signal processing:

• Jitter, an irregular time variation of period signal properties, such as small, unpredictable delays in scheduling
• Delay jitter, in packet switched networks, also called packet delay variation

In computer software:

• Jitter, a set of video processing extensions in the multimedia package Max
• JITter, a compiler that performs just-in-time compilation

In entertainment:

• Jitterbug, a dance
• Jitters (film) (Órói), a 2010 Icelandic film
• The Jitters, a Canadian band from the 1980s

In digital social media

• Jitter chat, an early and now-defunct online chat service

In optics

• Jitter, the oscillatory motion of the image with respect to the detector, which blurs the recorded image

In optics, jitter is used to refer to motion that has high temporal frequency relative to the integration/exposure time. This may result from vibration in an assembly or from the unstable hand of a photographer. Jitter is typically differentiated from smear, which has a lower frequency relative to the integration time. Whereas smear refers to a relatively constant rate during the integration/exposure time, jitter refers to a relatively sinusoidal motion during the integration/exposure time.

The equation for the optical Modulation transfer function associated with jitter is

$$MTF_{jitter}(k) =e^{-\frac {1} {2} k^2\sigma^2}$$
where k is the spatial frequency and σ is the amplitude of the jitter. Note that this frequency is in radians of phase per cycle. The equivalent expression in Hz is

MTF(u) = e
where u is the spatial frequency and σ is again the amplitude of the jitter.

For spacecraft, operation in a vacuum often means low mechanical damping. Meanwhile, spacecraft are compact and rigid, to withstand high launch loads. Jitter, then, is transmitted easily and often a limiting factor for high-resolution optics.