jitter

Jitter is a random variation in time or amplitude of the signal frequency, its phase or signal level. The International Telecommunication Union( ITU) defines jitter as: "Short-term fluctuations in the significant timing of a clock signal, deviating from their ideal temporal positions."

Jitter occurs in any electronic circuit and can adversely affect the transmission quality of voice or video, the quality of service of communications networks, the modulation of signals, Internet telephony, the logic levels of logic circuits, and more.

1. In data transmission, jitter refers to phase fluctuations and thus to changes in signal frequencies over time. These are fluctuations of fixed points in time, e.g. the time of transition from one signal amplitude of a digital signal to another. As a result, reference times can shift, which can lead to misinterpretation of signals, packet loss, variation in latency, and thus to degradation of transmission quality in real-time applications such as Internet telephony or video conferencing. Jitter occurs specifically at high frequencies, it is caused by noise and crosstalk, by interference, edge distortion, minimum level fluctuations, network congestion, and route changes, and can be measured with the eye diagram. Jitter is specified in parts per million( ppm) or in nanoseconds (ns). Jitter measurement has been standardized by the Audio Engineering Society( AES) under the AES17 standard.
   

   Jitter types

   Jitter is differentiated between random jitter( RJ), total jitter ( TJ), deterministic jitter ( DJ) and uncorrelated jitter (BUJ). There are various methods to compensate for jitter by precompensating edge distortions on the transmitter side or by correcting the jitter on the receiver side using mathematical algorithms.
2. In data transmission over IP networks, jitter is caused by latency in data packet transmissionbetween two systems. Such time shifts occur because some data pack ets require more time for transmission than others. For example, when routes are changed or when the network is overloaded. Jitter in IP networks is a particular burden on real-time communication, for example in Internet telephony or web conferencing.
3. In the case of compact discs(CDs) and DVDs, jitter is measured individually for all pits and lands and calculated as a mean standard deviation using statistical methods. The standard prescribes precise reference values.