[bob katz]

Jitter numbers are like CPU benchmarks. Everyone has a different method of measuring it, and very few people own the expensive analyser with sufficient resolution to do it justice. There are weighting figures and average and peak figures and peak to peak figures and it's a mess.

So you can't compare one manufacturer's jitter spec against another unless you find out EXACTLY how they measured it.

Most unfortunate. The method I use for determining jitter susceptibility of a DAC is Julian Dunn's jitter test signal and a spectrum analyser looking at the analog output. For A/D, an 11.025 or 12 kHz signal for 44.1/48 kHz, respectively will do, and look at a spectrum analyser. An excellent paper showing these measurements, which can be viewed visually, is at TC Electronic. Instead of looking at numbers in pico seconds, just look at the sidebands of the test tone on an FFT. If they're not right down near the noise floor, and the skirts aren't very narrow, then the jitter is, frankly, unacceptable. I reach that conclusion because I can hear the jitter in any situation I've ever encountered where the spikes measure more than a few dB above the 24 bit noise floor.

You can measure whether a converter is sensitive to jitter on an external input, measure WC versus AES sync versus internal. You can learn all you need to know with Spectrafoo, a clean test tone oscillator, and your brain.

And in fact, if every manufacturer were more honest, they would publish jitter tests with the same approach. Benchmark's A/Ds and D/As use this spectral analysis approach and it's very revealing. Pico seconds, shmeeko seconds.

BK