Friday, May 18, 2007


The colloquial or historical meaning of jitter is to shake or shudder one's body or limbs. Also:” Jittery" synonymous with "nervous" or "tense" to the extent of shaking, usually implying fear rather than excitement. May involve a neurological seizure, or withdrawal symptoms from drunkenness - Delirium tremens. Also: jitterbug - a dance that involved shaking the arms and legs.

In electronics and telecommunications, jitter is an unwanted variation of one or more signal characteristics, such as the interval between successive pulses, the amplitude of successive cycles, or the frequency or phase of successive cycles. Jitter is a significant factor in the design of almost all communications links.

Jitter can apply to a number of signal qualities, and can be quantified in the same terms as all time-varying signals. Also like other time-varying signals, jitter can be expressed in terms of spectral density. Jitter frequency is the time between the maximum and minimum effect of a jitter characteristic for a jitter that varies frequently with time. 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.

In the context of digital audio extraction from CDs "jitter" causes extracted audio samples to be doubled-up or skipped entirely. The problem occurs because the Philips CD requirement doesn't require block-accurate addressing. As a result, the extraction process will restart a few samples early or late, resulting in doubled or omitted samples. These glitches often sound like tiny repeating clicks during playback. An approach that has produced good results is to do jitter correction in software. This involves performing overlapping reads, and then sliding the data around to find overlaps at the edges. Most DAE programs will perform jitter correction.

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