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http://www.soundonsound.com/sos/feb07/a ... facing.htm
Jitter is a term that is often heard, but which few understand. It refers to uncertainty in the timing of a digital signal, and it can arise in various ways. However, it is normally only a problem in the context of A-D and D-A converters.
A poor-quality clock circuit can suffer from jitter if it is unstable, but this is pretty unusual in anything other than the cheapest digital consumer equipment these days. Of more practical relevance is the jitter that is induced in all cables and optical fibres. This comes about because cables inherently suffer capacitance and fibres suffer optical dispersion. In both cases, the effect is to blur the edges of the data pulses so that their timing becomes vague. The longer (or nastier) the cable or fibre, the worse the problem will be.
However, when transferring digital audio between two devices ? say, between a recorder and a DAW, or a console and digital reverb ? modest amounts of cable jitter have no effect whatever. The AES3 and ADAT interfaces are designed to accommodate a huge amount of timing variation and the jitter would have to be extraordinarily bad to cause any problems.
Where jitter does become significant is where the signal is being converted between the analogue and digital domains. Timing variations here will result in samples being measured or reconstructed at the wrong moment in time, and that equates to noise modulation or low-level tonal artefacts, and to stereo image instabilities.
These two diagrams illustrate how jitter is introduced into the audio signal, and the impact it can have on the signal.