The basics of PC audio

a) and b) I don't think RF interference is a concern with most systems

c) I'm almost positive that the USB port from the AirPort Express is not compatible with a USB DAC

d) once a file is compressed with a lossy format such as mp3 it can never be converted back

e) things constantly improve but the USB DAC is a mature format. It is basically the same DAC that has been around for 20 years with a slightly different interface to accept the digital data via USB rather than spdif.

a) Interference is a very local phenomenon. There's no way to know what will be necessary in your situation. But interference is also far less of a problem than you might imagine. (Think how many TV monitors are adjacent to preamps in home theaters.)

b) Ditto. Probably won't be a problem, but you never know till you try.

c) A wireless network is inherently less stable than a wired one. Cordless phones and microwaves can interfere with the connection. If you go the Express route, I'd connect a standard audio DAC to the audio out, rather than using a USB DAC. But sonically, it's probably a horse apiece in general, though specific set-up issues might be a factor.

d) You can convert an iTunes file (which is AAC, not MP3) to an AIFF file, but it won't be any better than the AAC file. Once a file is compressed with a lossy codec, there is no getting back the information that's lost. OTOH, mediocrity is in the ear of the beholder. For critical listening, you'd want full-resolution digital files (AIFF, WAV, or a lossless codec). But for casual or background use, you aren't going to notice that it's "only an MP3."

e) I don't know the USB DAC market well, but the only thing I'd worry about is noise. Assuming you can get adequate S/N from today's models, future improvements will be marginal.

I appreciate the responses. I hadn't realized that there's no going back from an MP3; though now that I think about it, it's very reasonable. Given that all I have are MP3s right now (and I have lots of them), the DAC on Airport Express should be more than adequate, I should think? Or, perhaps even the DAC in my laptop via the headphone jack would be adequate?

Thanks again,

Matt

d) Pabelson is corect, when I said it could not be converted back what I meant to say was that the information lost could not be recovered, but it can be converted to other formats.

c)

I'd connect a standard audio DAC to the audio out, rather than using a USB DAC.

??? If you use the audio outs from the express you don't need a DAC. The express USB port is for a printer and won't work with a DAC anyway.

The one weakness of the Express is jitter. (Jitter gets far more attention than it deserves, but in this case it's not just a theoretical concern.) Feeding the audio out digitally to a DAC would be better than using its analog output. Whether that improvement is worthwhile, given that you're already dealing with compressed files, is something you'll have to judge for yourself. I use my Express mostly to stream Internet radio, which is REALLY compressed, so a little jitter hardly matters. YMMV.