Optical vs. USB into DAC-is there a difference?

[bubruelz]

I am quite intrigued by the Micro DAC from headroom. I would like to know if the sound quality from usb would be the same, better, or inferior to the optical out of a computer's sound card. Does this depend on the sound card? I have also heard that usb is limited to 16 bit. Is this true, and would it affect sound quality? Thanks for sharing your knowledge.

 

[Solude]

Optical output is the ideal on PCs. Any other connection type will have electrical jitter in big numbers. The quality and feature set or lack there of the soundcard will ultimately determine the DACs performance. If it mangles the stream with resampling or attenuation than you're dealing with a degraded signal.

That USB is also limited to 16/44 isn't really the issue since a good chunk of your audio on PC is also 16/44. The problem is electrical, not data, jitter.

 

[Scrith]

In my current setup I have both the s/pdif and toslink output from my sound card (E-Mu 1212M) going to my DAC (Benchmark DAC1). The DAC1 provides a switch on the front that tells it which input to use, and I frequently find myself A/Bing between them to see if I can hear any difference. I've tried A/Bing between them while blind, with my wife switching it while my back is turned, and not blind, when I hear some problem in the music and I'm curious if it disappears with the other digital input...these are invariably problems in the original recording, verified by playing the CD on another system using the original CD.

So, I can't hear any difference between s/pdif and toslink in my current setup.

I often flip-flop about which input I want to use (optical is better from a computer, but coax is supposed to sound better, but my optical cable is supposed to be really good, but so is my coax cable, and so on) and have gotten to the point where I usually don't even know which one I'm using.

In the past, I found that coax sounded better (with a different set of cables...eBay glass vs. Elco UDC-S), but occasionally the coax setup would cause errors on my DAC1 (the red light would flash), usually when Windows was trying to play a sound on top of the ASIO output of Foobar. I am pretty sure this was a problem with the E-Mu drivers...however, I believe it is fixed now with their latest drivers...I haven't seen a red light flash on my DAC1 with coax input in a long, long time, even when playing a game like World of Warcraft with the sound on for hours while simultaneously playing FLACs with Foobar2000 using ASIO output.

 

[SunByrne]

OK, I'm confused.

I am fairly certain that digital coax carries S/PDIF just like TOSLink does. Are there substantial jitter differences between TOSLink and coax transmission of S/DIF?

Also, I've seen it said many times on this board that USB is jitter-resistant and therefore better than either TOSLink or coax, e.g. http://www6.head-fi.org/forums/showp...91&postcount=6 (one of many examples). Yet Solude, you're claiming that TOSLink is better.

So, what's the story here? If I have an external DAC which takes either TOSLink, coax, or USB, which really has the lowest jitter, and why?

 

[grandenigma1]

be your own judge... they each have their downfalls... usb being its bandwidth.

 

[Teerawit]

Quote:

Originally Posted by grandenigma1 be your own judge... they each have their downfalls... usb being its bandwidth.

Hey man...some like it 16/44...Scott Nixon fans do

 

[Solude]

Its a really easy decision in practice, even if you can't hear the differences in this case they are measurable.

PC audio, its critics will tell you over and over is nasty because of internal interference. All wired (usb, coax) transport have this problem. Its not a data jitter problem, a PC works so much faster than audio requirements and almost everything is buffered, checked and rechecked that getting the data out with good jitter numbers is easy.

The problem is the 'internal interference' rides on everything. So while the data jitter on bit perfect cards is good, the electrical jitter is nasty. Do a search on the Stereophile site for RME and have a look see. The sad part is the RME actually takes measures to make the electrical jitter less horrid

 

[dknightd]

I don't think there is an easy answer to this question. Ultimately I think it would depend on the computer, and the DAC being used. My guess (again this is only a guess) the would depend on the details of each device.
My guess (repeat guess) would be that you'd here more difference between two different DACS than you would between one DAC being fed by toslink vs. USB.
If you are using standard redbook CD's as source the bandwidth limitations of USB should not be a problem (unless you were trying to move more than a few stereo digital signals across the usb at the same time).

You might want to ask headroom what they think for their micro dac. If you do, let us know what they tell you.

 

[tschanrm]

Quote:

Also, I've seen it said many times on this board that USB is jitter-resistant and therefore better than either TOSLink or coax, e.g.

Yes, asynchronous USB transfers is basically jitter free. Although, Isochronous USB transfers, the transmission most USB sound devices use, can be just as prone to jitter as S/PDIF protocol. Ti's implementation reduces this jitter by having the computer slave to the clock inside the TI chip (although not sure of other USB chip manufacturers). I found a couple of posts on the following thread that talk about this:

http://www6.head-fi.org/forums/showthread.php?t=74248


EDIT:
Quote:

Are there substantial jitter differences between TOSLink and coax transmission of S/DIF?

(Sorry, a little off-topic) Yes, there can be. It's all in the implementation of the link. For the computer, it seems that optical is the lower jitter of the two due to a physical electrical connection used for coaxial (as mentioned by Solude above), but it may not always be the case if both are designed well. Here's an old review of "jitter reducing" boxes, but it gives you an idea of just how much of a difference improper implementation can be:

http://www.monarchyaudio.com/DIP4.htm