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?"

Comments

Use TOSLINK instead

[RzUpAnmsCwrds]

SPDIF outputs are usually pretty consistent at passing the PCM data or the DD/DTS sountrack if you have them configured right.

Some cards, however, such as Creative's Audigy series, are notorious for resampling inputs/outputs, so you might want to check.

Even a cheap card, like the $15 cards on Newegg, should provide a clean output. Don't buy the garbage about "jitter" that I'm sure someone will bring up - so long as your card and cabling are operating within the specification, you won't have any problems.

Do consider TOSLINK instead, however. TOSLINK uses fiber-optics, so your audio equipment and PC are electrically isolated. This reduces the chance of creating a ground loop or introducing RF noise into your reciever/amp. Moreover, it protects your equipment in the event of an electrical mishap.

Re:Use TOSLINK instead

[FlexAgain]

RzUpAnmsCwrds (262647) wrote
Do consider TOSLINK instead, however. TOSLINK uses fiber-optics, so your audio equipment and PC are electrically isolated. This reduces the chance of creating a ground loop or introducing RF noise into your reciever/amp. Moreover, it protects your equipment in the event of an electrical mishap.

One slight clarification, TOSLINK normally does carry SPDIF. TOSLINK is primarily just detailing the physical medium, the data is still encoded as SPDIF (which can also be carried on wire). The original author didn't specify how he was intending to use SPDIF, it may have been over either medium.

Jitter is a bunch of crap

[Hidyman]

We are talking digital signals here.
Any self respecting DAC circuit will not be affected by jitter.
I use toslink all the time and there is no problem with "jitter".

Jitter is marketing hype.

$25 TOSLINK card

[hab136]

I've been using a Chaintech AV-710 with my linux home theater PC for a long time now (a year?), outputs to my surround sound receiver. Fully supported under ALSA. mplayer, xine, and ogle all pass through the AC3 5.1 sound for my receiver to decode. I went for fiber optic, mainly because I didn't want to worry about grounding effects.

Chaintech's product page

There are Consumer and Pro modes

[Marillion]

The S/PDIF protocol has a consumer mode and a professional mode. I do some professional audio work and my DiO-2496 will emit both. My MD player will only accept the consumer mode which includes Serial Copy Management System (SCMS) flags which indicates if the source is first generation (allowed) or second generation (not allowed). The other nice thing about this card, it is completely ignores inbound SCMS and can re-code a second generation stream as a first generation consumer stream or a professional stream. Haven't needed it, but cool. I've connected it to professional DAT units, consumer MD units and DVD players.