The question of sample-clock quality is a perennial one for digital audio equipment designers. Yet most chip makers provide very little information about the jitter performance of their products. Consequently, equipment designers sometimes get burnt by jitter issues. The increasing use of packet-based communications and class-D amplification will throw these matters into sharp relief. This paper reviews various ways of characterizing and quantifying jitter, and refines several of them for audio purposes. It also attempts to present a common, unambiguous terminology. The focus includes wideband jitter, baseband jitter, jitter spectra, period jitter, long-term jitter and jitter signatures. Comments are made on jitter transfer through phase-locked loops and on the jitter susceptibility of audio converters.
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