Is all coax/optical spdif output created equal?

**Choser** · 02-03-2004, 12:49 PM

My carputer that I am planning will eventually do many things, but first and foremost is sound quality. I want it to rival some of the best non-carputer audio setups, which I know is going to be difficult.

I'm reading that many people who are interested in sound quality are forgoing the onboard audio, and are choosing a high end creative labs or even m-audio sound cards. Understandable, these cards kick ***. I can really picture why their analog outputs sound better... they use higher quality components, better shielded from noise, and they output a higher signal voltage.

However, in the interest of sound quality - spdif is where its at. Since my carputer is going to be in the front of the car, I want to use coax digital output, which would go to a signal processor/ line driver in the trunk, right next to my amps. A 9volt rca signal running through just a 1 meter rca should be pretty clean!

I've always been under the impression that digital is digital is digital. The relatively cheap on board digital output should be pretty much the same as the best audio output on the creative and m-audio cards. Am I wrong? I can picture that the componentry on the cheaper on board audio is of lower quality, and would let more noise interfere with that digital signal... and that digital output may be of a lower voltage... but you would need a lot of noise to effect the spdif signal, from what I know. If I have to buy an add on card, I will, no biggie - but I want to avoid that added complexity for the small space/cost/power savings. Thank you very much!

**unsavory** · 02-03-2004, 04:58 PM

Hmmm. My gut would be to try it out first before making any additional purchases. Why not?

**Choser** · 02-03-2004, 05:14 PM

I like your gut....

I would - but... if I need an additional sound card then that totally changes the plans for my system. I want it to be tucked into an area and be completely PCI-less. If I install a PCI sound card, that also changes my power demands. If I can't squeeze a unit into the glvoe box, I may as well get a more powerful motherboard and do everything with PCI.

**greenglo** · 02-03-2004, 05:18 PM

When your soundcard outputs digital sound it does it in the form of PCM. Which if you do your reading is just an analog signal sent digitally. I'm pretty sure this is true because my receivers PCM indicator comes on when it gets a digital signal from my soundcard or from a cd in the dvd player.

**Choser** · 02-03-2004, 05:51 PM

Yeah exactly. Digital output should be the same from one device to the next. Only analog devices are effected by noise, more or less.

The exception is if the noise levels are great enough to where they eclipse the threshold of whatever is decoding and mistake the noise for a bit. I aws just wondering if anyone was unsatisfied with built in digital output, and upgraded.

**killerfishes** · 02-03-2004, 06:21 PM

you are planing the same thing i am. im planing on doing soundoff comp in SQ. I am going to use spdif. Im starting with the m10000 that has a spdif out on it to a H-700.
if its spdif then it must be 48khz digital out. this page will tell you the pros and cons of optic vs. coax http://www.cobaltcable.com/newslette...02.htm#toslink
but this is interesting "We believe that any audible difference between the two connections stems from differences in the quality of the electronics, NOT the type of connection. For example, if a CD player uses superior quality components for its Coax digital audio connection and inferior components for its Toslink connection, then it is reasonable to assume that the Coax could have superior sound quality."
so who knows.

**henkbliek** · 02-03-2004, 07:10 PM

First of all the logic signal on coax or optical connections is exactly the same. I think that the [audiophile] superiority of the average coax (75ohms) connection over the average toslink connection is caused by the insertion of two more active devices in the link (the transmitter and the receiver). In a car setup however, I think that an optical connection will be far more superior because it is not influenced by electronic and magnetic fields.
Imagine your coax connection running alongside some switching signal. Then it is quite possible that the inductive or whatever kind of coupling between the cables causes enough level shift to be mistaken as a logic transition... It also avoids ground loops, which may introduce noise in your analog signals, even if they are introduced by the digital link.

**Choser** · 02-03-2004, 07:31 PM

Actually - my question was more in regards to the various manufacturers of sound cards.

I have read the differences between coax and optical before, and decided that in most situations, it really doesn't matter. Just use whatever is most convenient.

But I was wondering if anyone had some input as to whether or not the epia m's digital output was of just as good quality as lets say, an m-audio pci card.

**tbdombrosky** · 02-03-2004, 08:10 PM

Originally Posted by Choser

Actually - my question was more in regards to the various manufacturers of sound cards.

I have read the differences between coax and optical before, and decided that in most situations, it really doesn't matter. Just use whatever is most convenient.

But I was wondering if anyone had some input as to whether or not the epia m's digital output was of just as good quality as lets say, an m-audio pci card.

Watch out, they are different. Some cards do resample before they send data out the spdif ports. Creative cards, nvidia soundstorm does, some others too. The ones that don't sound a lot better. You can tell easily in Windows by using the master volume slider. If you can adjust the volume with it, then the card resamples. If the wave volume is the only slider that affects the sound, then it doesn't resample. My old EPIA board didn't resample. I don't know how the newer ones are though. You won't notice the difference when using spdif between a $1000 card and an onboard soundcard if they both don't resample (some audiophiles may tell you otherwise though)

Also, an optical cable will offer no benefit over a coaxial cable in the car with regards to interference. When a signal is digital, it's not subject to interference. When it's converted to analog, that's when you have to worry. So a digital coaxial connection as well as optical connection will not be subjected to things like ground loops.

Tom