[time-nuts] Sound cards

Magnus Danielson 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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