Thread: Is all coax/optical spdif output created equal?

no. i will bet money on it i have the same AC97 audio chip in my msi im on right now and if spdif is set to 48khz it will not resample. DO NOT CHANGE TO 44Khz.
as for ground loop. it will only be a problem if you had one to start with. look on the page i posted, it talks about this.

Originally Posted by tbdombrosky

If you could explain this a little more that would be great because some of us might need the education (ok, just me then). I was under the impression that it is not affected by the chassis ground because the signal is 1's and 0's. So you're saying a dvi cable for example can also introduce noise? Thanks.

Yes, the signal is just 1's and 0's, in the real world these signals are represented by voltage levels. Now imagine some pulse being induced on the signal. With an ordinary analog signal you won't hear this (if it's short enough, let's say a couple of microseconds). In the digital line, this pulse will result in a changed bitvalue, so 1 can become 0 and vv. just because the '1' is only 1/4V in reallife (SPDIF) If this happens to be one of the most significant bits in the audioword, this will result in an audible tick.

And yes, also a DVI cable can be influenced by noise and interference, however I believe DVI uses differential signals, this way the interference will be cancelled out by the receiver (if the absolute level is not too severe). This is also an option for digital audio; you would than use AES/EBU wiring, this uses balanced (110ohms) cable, XLR connections and transformers on both sides of the link.


And about the [electrical] quality of the SPDIF output; I believe that an SPDIF output should have an output transformer, the M has not.
Apart from that the output signal is a rather decent ~410mVpp squarewave signal, which drops to ~170mV when loaded. I think that's ok.

Other guys know much more about resampling, oversampling and things like that so I won't go into that. But keep in mind that no resampling also means no volume control... Doesn't sound very convenient to me...

Originally Posted by Choser

170mV? As in .17 volt? Dang.

Is that good enough for a run to the back of the car?

As to no volume control... I thought you did have volume control, its just that you had to use the individual slider for wave output.

You can run such signal over a couple of meters without trouble. A normal audio signal (to amps in the truck for instance) has the acoustic detail in the uV range.

Does it matter where the original digital audiostream gets recalculated? I don't think so, distortion caused by volume or channel gain scaling will be much worse than the distortion introduced by some resampling stuff.

Something else you should keep in mind; If you control the volume in the digital domain, then you will loose output resolution.
When you play with volume at 100%, then you'll use (and hear) the full 16-bit range of the signal (until you're deaf of course ).
Now, if you turn the level to more acceptable level, you'll loose resolution, 1 bit for every 3dB down. Let's say you play at 24dB below max volume, that is 8 times 3dB down or 1 bit unused. This leaves you with 8-bit of usable resolution... Do you recall how your 80's Atari sounded?

[Maybe I missed some dB's here and there, but this is the idea. True Hifi geeks can give you all the nasty details for sure. Hint: www.diyaudio.com ]