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Question about digital audio

post #1 of 4
Thread Starter 
SO, I am making a DIY amp.

I'm working out of my college's lab, which has plenty of equipment for building and testing laboratory grade amplifiers, transducers, etc.

I'm working on my enclosure with one of the techs and complaining how my 5.1 speakers take up all the line outs on my Audigy 2, and that I was thinking of putting a DAC in my amp so I could use the digital out but was worried about the cost.

He says "Oh, try this" and reaches into his drawer and pulls out three $100 sigle-channel laboratory grade 24-bit DACs that I can just have for my own entertainment. NATURALLY I can't pass this up.

At any rate, my question is this: How dependant is the audio quality of the digital out on the source? For instance if I take SPDIF out from an Audigy 2 and a really top-end source and feed it into the same DAC and amp how similar would the sound be? I guess my reasoning is that you are encoding the same signal, and since it is digital it can't really distort or anything unless you are getting bit errors, which I wouldn't think would be a problem.

Thanks

EDIT: Assuming that both the top-end source and the Audigy 2 are playing the same format media, and a good player (foobar) is being used on the computer
post #2 of 4
I'm a bit lost. It is obvious that when exactly same sets of digital data are feed through DACs, outputs are the same. If you are asking if the high end source and Audigy 2 will provide similar/same digital audio signals for your DIY DAC, then the answer is possibly yes.

44.1Khz encoded wave file in PC should be the same or fairly close to what a reference transport CD player may output digitally if jitter/error was minimum (while encording wave file). The quality of sound is more dependent on quality/characteristic of DAC and/or filter. For lossy type, digital outputs vary significantly between system to system (i.e., how to fill in missing information or smoothing out rough transitions).

Now the question is how much effect would jitter and/or error have on the digital output? Well this is highly debatable but I think there are far less jitter/error related problems than what most of audiophiles worry about. Of course you mileage may vary, but I would not recommend any intermediate/beginner DIY person to work on DACs. Unless you are working with a printed circuit board with descent powersupply, results were typically less than optimum.
post #3 of 4
Quote:
Originally Posted by go_vtec
It is obvious that when exactly same sets of digital data are feed through DACs, outputs are the same.
But the input to a DAC as a matter of fact is not just the digital data alone, also the *time* at which each little bit of data arrives represents effective input that changes the ouput of the DAC. Timing errors in the digital stream (jitter) allegedly make audible differences, even though the digital data is exactly the same.
post #4 of 4
Quote:
Originally Posted by Porksoda
At any rate, my question is this: How dependant is the audio quality of the digital out on the source? For instance if I take SPDIF out from an Audigy 2 and a really top-end source and feed it into the same DAC and amp how similar would the sound be? I guess my reasoning is that you are encoding the same signal, and since it is digital it can't really distort or anything unless you are getting bit errors, which I wouldn't think would be a problem.
The Audigy 2 does not output a clean digital signal. It resamples CDs up to 48kHz using a very poor algorithm, then outputs the result on its digital output. There is no way to avoid this. This is fine for gaming, but unsuitable for music. If you're using expensive DACs, you owe it to yourself to buy something like the $20 Chaintech card to get a clean 44.1kHz digital output. I've verified that that card generates a bit-perfect digital output when using the M-Audio Dio2448 drivers. (I never could get a bit-perfect digital output on that card using the official Chaintech drivers, but that was a year ago and there are newer drivers, so perhaps the problem has been fixed.)

There is no Creative card in production that produces a good digital output, except for the recent E-MU line of cards.
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