[time-nuts] Sound cards
magnus at rubidium.dyndns.org
Tue Jan 13 15:21:04 EST 2009
J.D. Bakker skrev:
>> Maybe I lost track and missed something, but I don't think I ever saw
>> more on the subject of specific high-end sound cards that might be
>> useful for nutty measurements.
> From an earlier list message:
>> [F]or best noise/jitter-performance an external ADC should be used,
>> connected through a digital link to a PC sound card. One could do a
>> lot worse than the TI PCM4222 eval board
>> (http://focus.ti.com/docs/prod/folders/print/pcm4222.html), which
>> accepts an external clock if so desired. At $149 (plus a tenner or
>> two for the sound card) this will likely be much cheaper than an
>> equivalent FireWire-device.
> The digital link in question is S/PDIF; with the current popularity
> of Home Theater systems cheap cards with digital I/O have become
> quite prevalent. As an added bonus, S/PDIF can be run over both
> coaxial and optical media, the latter being attractive in further
> isolating PC noise from any measurement setup. And of course, a
> manufacturer's evaluation board is much better documented and more
> suited to measurement-specific mods than a random sound card.
The optical link commonly being used for S/P-DIF is TosLink and it seems
like it can be the cause of many problems. It seems like some care in
doing the optical link setup is needed. I have never digged into why the
optical links have that problem. I can only guess, but bad optical
coupling seems reasonable. The multimode "fiber" seems to be leaving one
or two things to ask for.
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