[LAU] Aliasing noise when going D->A->A->D

[Ken Restivo]

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I've noticed a nasty aliasing noise when connecting an analog output from a digital source, to the analog input of another digital device.

For example, going out of a cheap soundcard on a PC, into a nice (or cheap) A-D converter, an ugly high-pitched aliasing noise appears even with no program data. It's not audible to my ears when listening just to the analog output of the hda-intel; one must plug its output into an A-D in order to hear it, and then it's rather loud.

I've noticed this with my expensive Edirol firewire interface and with my cheap Audiophile USB interface. The common factor is when the sound being digitized comes from an ugly hda-intel sound chip. All three are running 48khz

Would this happen even with expensive D-A's?  Is this a common problem when connecting D-A back to A-D?

I'm asking because I'm going to have to plug the analog outs from one of these interfaces (the firewire or the USB, not the hda-intel) into someone's PresonusFirebox/ProTools rig on Friday, and I want to know if I'm going to have to deal with this aliasing noise. 

He runs at 96Khz, IIRC. I dunno if that will make the noise better, or worse. It'd be nice to go S/PDIF out, but I don't know if that'll work either, if the sample rates don't match.

- -ken
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