Hi - I am trying to set up a music system with a Mac Mini as my server. I am trying to decide whether I would benefit from a USB DAC or whether I could simply get a DAC with an optical S/PDIF input. Is one connection "better" than the other? I have read somewhere that USB allegedly has some advantages (I am not quite sure what those would be, though), but it may depend on how the attached equipment interacts with the Mac. The other question then is, whether my downstream system (amp, speakers, and my ears) would be good enough to hear the differences, but that's a question for another day.

So, what's the current status of the discussion?

Thanks so much. Best - MM

Is one connection "better" than the other?

There's no correct answer to this question, it'll always come back to whatever your weakest link is anyway, and no one has the same set of equipment, listening environment, musical tastes, and ability to discern meaningful differences in true double-blind comparisons.

I'd say most of us here, though, are perfectly happy within the iTunes ecosystem, sending bit-perfect Apple lossless out the built-in optical port of a Mac and/or the optical out of an Airport express into an AVR--with no DAC.

A much smaller percentage here have a USB DAC, some go analog, some digital, and they swear by them. These also tend to be the folks who don't like the iTunes ecosystem, and tend to rip and tag with other software.

So, what's the current status of the discussion?

I'm not sure there is one, it's too subjective, too price-sensitive and, often, too inconclusive.

Thanks so much for the info.

I know what you are talking about with respect to the question of getting a separate DAC or not. However, I am not planning on using a receiver, just an amp (or amps, plural, perhaps), so I will need a DAC somewhere. Anyway, I didn't want to get into a discussion about DACs, so let me rephrase my question:

Which one of the two digital output options (optical or USB) provides the cleaner signal? Is the optical out really bit-perfect? I couldn't find much info on that.

Thanks again. Best - MM

Yeah, if you want to talk Mac and DAC, there have been a couple of good older threads here which got into them, and users talked about what they use and why--you'd have to dig back for them. Also there are a couple of DAC manufacturers who post over here:

http://www.audioasylum.com/forums/pcaudio/bbs.html

Not all of them are completely self-serving in their perspective. I don't post there, though I often find the threads amusing. The Windows signal to noise ratio is a little too high over there for my tastes, but Macs and DACs do get discussed--including what you're specifically interested in, is it better to go optical or not.

In OS X, yes, with iTunes optical out is bit-perfect--so, too, if streamed to an Airport express and out its optical port. You can test it yourself with a high res DTS 5.1 audio file. If you do a lot of switching back and forth between software players and also do video with Front Row and/or also run EyeTV, you may find you have to go into Audio MIDI from time to time to reset things, but that's no problem. It can get stuck sometimes and if you're sensitive, you'll hear when it's resampling 44.1 up to 48.

I have a H/K AVR 745 that has a USB port also (for audio as well as firmware upgrades). Several months ago I tested this port for iTunes on my Mac and it works great. The Mac (as well as a Windows XP PC) identified my receiver as a USB A/V receiver. I can do some tests on two channel content from iTunes to see if the USB or optical works better. I have it connected through optical right now. I need to find a longer USB cable though since my imac is about 10 feet away from the receiver. BTW, my speakers are Klipsch Reference series RF5. The 745 receiver is highly regarded for its sonic qualities.

Gotta agree with chefklc.
I don't think there's a definitive answer - and in practical fact it depends more on what you've got available to use. I have heard that a USB connection could be better to reduce jitter - but that was coming from someone selling a USB DAC...

I think I have a better grip on things by now. I will go with a USB DAC, simply for the fact that they usually come with an S/PDIF input, and so I would have both of them to play around with.

Now I'm off to look for a decent USB DAC in the <$400 range. I don't really want to spring for a Benchmark or Bel Canto et al.

Thanks guys!

Best - MM

I ended up with a Citypulse 7.2x II DAC. I'm driving a small tube amp with it, using TOSLINK input from my iMac and some small Paradigm bookshelf speakers. This is a decent little unit and has selectable oversampling. I'm running it right now in a bit-perfect setup (44.1/16). It will take a 96 or 48 signal fine.

I decided to go TOSLINK / S/PDIF vs. USB. I read a lot of hassles using USB and didn't want to spring for a DAC1 for the office system. I don't think most USB devices will take a signal over 44.1/16 w/o custom drivers. I believe the DAC1 is an exception here.

I've had the DAC for about a week now and am happy with it, especially given the price. I cannot even describe how much more resolving this DAC sounds compared to the built-in DAC on my iMac. I've been running it non-stop for a week and it is getting smoother and smoother sounding.

Regardless, there are a TON of options out there. Checkout head-fi.org too.

here's a response from an EE, take it for what it's worth.

Optical (S/PDIF) has little to no signal degradation through the transfer medium (aka cable). For that matter, as long as your receiver is well isolated from noise on the power supply (mostly ground noise), your output should be clean.

USB uses LVDS (low voltage differential signaling), which has the advantage of high common-mode noise rejection. By that, I mean if some noise couples onto your cable between the computer and receiver, this noise will not change the magnitude of the difference of the differential signal. When the DAC finally receives the signal and decodes it, the input is fairly stable/clean. USB however, is not electrically isolated, so noise on the ground line of the source may show up on the ground line of the receiver, creating unclean output.

So, with that said, S/PDIF is better, but I doubt you'll notice enough difference. A good DAC/Amp design will make far more difference than debating between S/PDIF vs. USB.