Phil Karn wrote:
Even if that jitter were directly imposed on the local VCO, which it is not because of loop filtering, it would still be reduced by a factor of 64 as the VCO clock is divided by 64 to produce the DAC sample clock.
I'm going to have to revise and correct this. (In my defense, I've been home sick with the flu for the past few days, and I'm not firing on all cylinders.)
When the VCO clock is divided by 64 to obtain the 44.1 KHz sample clock, the jitter time is *not* divided by 64.
With this correction, I believe the rest of my analysis remains valid. That is, the clock division by 64 reduces the modulation index of the jitter on audio components by that same factor. So 5ns of jitter (a little more than that scope showed) represents only 1/10,000 of a cycle of a 20 KHz sine wave (period 50 microsec). And the modulation index would be proportionately lower at lower audio frequencies; down at 1 KHz, where there's far more energy in a typical audio signal, 5 ns would be only 5/1000000 (5 millionths) of an audio cycle! These are truly *tiny* phase modulation indices that would produce very little in the way of PM/FM sidebands. I just can't imagine that anyone could hear them.
And I've left out the effects of PLL smoothing, which reduces jitter even further.
But if you feel otherwise, conduct some properly controlled listening tests. I'm all ears.
--Phil _______________________________________________ Discuss mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/discuss
