FA: > On Wed, Nov 11, 2009 at 10:59:39PM +0000, Folderol wrote: > > > An entire cycle of 48kHz is about 20 uS so jitter would have to be > > significantly less than that to avoid 'cogging'. > > It's not the amplitude of the jitter that matters but > the spectrum. Even the best and most expensive audio > cards have lots of very low frequency jitter. And if > you lock them to an external reference the local VLF > jitter is replaced by that of the reference (within > the PLL bandwidth). > > Jitter creates phase modulation, and the amplitude > of the sidebands increases with signal frequency. > To have a clean top end any non-VLF jitter should > be below a nanosecond or so. It's not so difficult > at all to achieve this with a PLL provided the > reference is stable. > > Syncing two or more cards (so they will produce > time-aligned samples if given the same analog input) > is another matter. But if the 'soundcard' is dedicated > hardware there are relatively simple solutions for that. So..., as a first try it is better to do a multi channel card, than to do multiple single channel ones and try to make them sync ? Regards, /Karl ----------------------------------------------------------------------- Karl Hammar Aspö Data karl@xxxxxxxxxxx Lilla Aspö 148 Networks S-742 94 Östhammar +46 173 140 57 Computers Sweden +46 70 511 97 84 Consulting -----------------------------------------------------------------------
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