Very interesting measurements indeed. For anyone interested, the subject of jitter and its audibility is well discussed in the literature with one Julian Dunn being the recognized expert. Here is an excellent application note detailing this very topic...
http://www.audioprecision.com/bin/tn23.pdf Another set of gentlemen, Eric Benjamin and Benjamin Gannon conducted research on test subjects to determine the minimum audible limit of jitter. They found it to be 10ns rms with test tones and 20ns rms with music. Lest you not be convinced by mere listening panel observations, one can determine the absolute theoretical audibility of jitter by simply requireing the error induced by jitter to be lower than the quantization level of the format...namely 16 bits with the worst case input signal...a fullscale 20KHz sinusoid. Let V(t) = A*sin(w*t). Now differentiate to find the max slew rate dV(t)/dt = A*2*pi*f*sin(2*pi*f*t) The max slope of a sinusoid is 1 and therefore the max slew rate is 2*pi*f*A Let A = 325768 (max fullscale signal) f = 20000 which gives a max slew rate of 4.11 bits/ ns and thus if the jitter is less than 1/4.11e9 = 243ps peak then there cannot be a single LSB change. Now this is somewhat arbitrary and does not consider sideband modulation due to the spectral content of the jitter and the fact that humans can hear tones that are deeply buried in noise. The accepted theoretical dynamic range of the compact disc format is 120dB when properly dithered. Thus one could require the jitter be another 24dB lower (the quantization noise for 16 bits = 16*6.02 = 96dB) or 244ps / 15.8 = 15.4ps. In any event, the jitter of the Squeezebox 2 is very low indeed. Well Done Slim Devices! -- MarcBernard _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
