Originally Posted by baglunch
Why is SPDIF better than USB? Aren't they both digital signals? Why would one be an improvement over the other?
I've seen DAC's that have USB and SPDIF inputs, and everyone says the SPDIF input sounds much better, and I've seen USB to SPDIF converters.... so why not just do that inside a USB DAC if it is such an improvement? And why is it an improvement? Why would one lossless digital signal sound better than another?
Many reasons actually
-<$1K USB DAC's boil down between the crummy sounding PCM270x USB controllers(16/48 max) and more recently the Tenor chip(24/96 max) but those 2 chips carry an horrid jitter
-until very recently, you couldn't get galvanic isolation over USB...the ADUM4160 chip has come to save the day, and many companies sell it in dongles now. Most serious S/PDIF interfaces provide galvanic isolation over their coax output(using pulse transformers) and toslink being a light signal it's also fully immune to electric interferences. A proper galvanic isolation ensures that your computer dirty ground doesn't reach your audio gear.
-There's many ways to reclock S/PDIF in order to obtain a lower jitter, the WM8804(50ps) and CS2000(75ps) chips come to mind
The very best solution is to slave the transport to the DAC, but the DAC's offering this option are uber-pricey...basically the DAC has its own clocking and slaves the computer to it via a discrete clock signal.
The shortcomings of:
-USB are jitter and galvanic isolation
-S/PDIF are explained here: http://www.gearslutz.com/board/so-much-gear-so-little-time/172143-spdif-vs-word-clock-question.html
"S/PDIF is a horrendously poorly designed interface. This is because it combines the clock and audio coding onto the same signal. The receiver is supposed to recover the clock from this signal as well as extract the audio data. This turns out to be a non-trivial task, and one that almost always leaves the recovered clock contaminated with signal correlated jitter artefacts."
Some companies sell async USB controllers that would supposedly fix the jitter problem, but it's very rare that they also provide galvanic isolation....also some other companies call bs on the async arguments(click on "Design Philosophy"): http://www.centrance.com/products/dacport/
"Some manufacturers may lead you to believe that Asynchronous USB transfers are superior to Adaptive USB transfers. This no more true than saying that you "must" hold the fork in your left hand."
Edited by leeperry - 9/15/10 at 6:54am