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Is All SPDIF Audio Output the Same?
CyberSpaZtiK asks: "I am going to build a Linux audio appliance to hold my music collection in various formats and for output to my stereo system. Because of a probable lack of Linux availability or support for audio cards with high quality D/A converters and low-noise electronics (or am I mistaken?), I want to keep the output path completelely digital by using a card with SPDIF output. However, it occurs to me that I actually know very little about SPDIF - are all SPDIF outputs made equal? Can I expect every SPDIF interface to emit the exact PCM data of the source audio, or are there over/under-sampling/aliasing, etc. issues that you sometimes get with digital signal processing? What do I need to understand about SPDIF and/or other digital output interfaces to make an informed decision?"
Well, I should say that I wanted to build a living room "jukebox" and DVR for parties, so my requirements might be a bit different from yours. I've used Mserv because I wanted a kiosk-type jukebox that would act like a real jukebox. That is, if no songs were selected, it would start picking songs based on ratings and how long it had been since they had last been played. I don't know of any other jukeboxes, Windows or Mac (perhaps someone can enlighten me) that will weight it's random selections like that. I wrote my own kiosk-style frontend using Python, but it appears that someone else has done the same thing with Shrill, complete with album art. I have a friend who's doing something similar with MPD, but I haven't used it myself. I've also played around with MythTV, which was nice because of the DVR features, but it didn't have the random feature that I wanted.
Actually, Jitter is a real, audible and nasty issue in certain specific applications... but not this one.
It's not a problem you are ever likely to come across outside a big recording studio where several devices are talking to each other digitally with DAC clocks drifiting compared to each other (oh, and it's easliy solved, the solution is to slave everything to a master clock).
The problem of sending a 44.1kHz signal from one end of your house to another is trivial compared to feeding a broadband signal from your ISP to your computer, and you never have jitter issues there.
A pizza of radius z and thickness a has a volume of pi z z a
...of course if you are trying to avoid wires (almost) entirely, you can try beaming your SPDIF outputs over a home 2.4 Ghz video sender pair (e.g. as sold by Radio Shack). Plug the coax SPDIF into the video input of the sender and, on the other side, pull the SPDIF off the video receiver into your stereo's amplifier. It sound's crazy, but the video sender is the only non-network wireless device with the bandwidth to pull off this trick. This is good to the limit of the video sender (less than 100 ft) and noise free...so long as you avoid 802.11b/g frequencies. It seems to be microwave immune, but will be interrupted if people walk across the line of sight. In short, you can get digital wireless sound for the cost of an analog video sender. Apparently I'm not alone: http://www.andrewkilpatrick.org/mind/spdif/