Jitter is the time variation of a characteristic of a periodic signal in electronics and telecommunications, often in relation to a reference clock source. 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 (e.g., USB, PCI-e, SATA, OC-48). In clock recovery applications it is called timing jitter. Wolaver, 1991, p.211
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Jitter is the time variation of a characteristic of a periodic signal in electronics and telecommunications, often in relation to a reference clock source. 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 (e.g., USB, PCI-e, SATA, OC-48). In clock recovery applications it is called timing jitter. Wolaver, 1991, p.211
Jitter can be quantified in the same terms as all time-varying signals, e.g., RMS, or peak-to-peak displacement. Also like other time-varying signals, jitter can be expressed in terms of spectral density (frequency content).
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. Generally, very low jitter frequency is not of interest in designing systems, and the low-frequency cutoff for jitter is typically specified at 1 Hz.
Packet jitter in computer networks
main: Packet delay variation In the context of computer networks, the term jitter is often used as a measure of the variability over time of the packet latency across a network. However, for this use, the term is imprecise. The standards-based term is packet delay variation (PDV). PDV is an important quality of service factor in assessment of network performance. A network with constant latency has no variation (or jitter). Packet jitter is expressed as an average of the deviation from the network mean latency.
Compact disc seek jitter
In the context of digital audio extraction from Compact Discs, seek jitter causes extracted audio samples to be doubled-up or skipped entirely if the Compact Disc drive re-seeks. The problem occurs during seeking because the Red Book (audio CD standard) does not require block-accurate addressing. As a result, the extraction process may restart a few samples early or late, resulting in doubled or omitted samples. These glitches often sound like tiny repeating clicks during playback. A successful approach of correction in software involves performing overlapping reads and fitting the data to find overlaps at the edges. Most extraction programs perform seek jitter correction. CD manufacturers avoid seek jitter by extracting the entire disc in one continuous read operation using special CD drive models at slower speeds so the drive does not re-seek.
Due to additional sector level addressing added in the Yellow Book (CD standard), CD-ROM data discs are not subject to seek jitter.
A jitter meter is a testing instrument for measuring clock jitter values, and is used in manufacturing DVD and CD-ROM discs.
