Originally Posted by scorch123
I have demo'd USB dacs in my PC-based system and have not heard major audible differences between them and my PCI-based RME card. "Very jittery" needs to be backed up with jitter/Thd measurements, IMHO.
- Steve O.
If you want to get technical there are several different modes USB can run in, based on the Windows drivers. The really horrible one is synchronous mode. Which many cheap USB devices use. There is zero error correction of any kind used in this mode. And it uses a fixed clock which makes it virtually impossible to generate 44.1Khz. It's essentially fixed at 48Khz. Jitter in this mode is off the charts, and that has been backed up many times. I agree that in general jitter is an overblown issue, but this is extreme jitter. If you care at all about audio quality stay far far away from devices using synchronous mode. Which can usually be identified by running only at 48Khz.
Asynchronous mode, which is very flexible and allows any clock speed you want, would be great. Too bad nobody uses it.
Adaptive mode is what most decent devices use. It's better than synchronous, but still not great.
Or you can do what Emu does and throw all that out the window. They wrote their own standard which runs in what is essentially asynchronous mode with some fancy error correction, and they reclock the data at the other end. This is probably overkill, and I wouldn't pay a premium for it. But the 0404 is pretty cheap.
As for proof I've heard it many times myself. The 0404 supports ASIO, but only through it's own drivers since the timing is totally different. Using the standard ASIO drivers in Winamp produces all sorts of clicks and pops and dropouts. That's an extreme case where the source is completely out of sync with the card, but I've heard many people complaining of the same thing with cheaper synchronous USB sound cards.