DAC Input: Coaxial vs. Optical

I finally picked up a coaxial cable for my Benchmark DAC1 and was able to test it side-by-side against my eBay (SonicWave) glass toslink cable. My source, an E-MU 1212M, makes this very simple when combined with a DAC1...the 1212M has both outputs active at the same time (and even gives the option of using either AES/EBU format or S/PDIF on the coaxial output via a button in the software...I used AES/EBU format for the tests, because supposedly it is the "professional" format), and the DAC1 supports both inputs with a toggle on the front that lets you easily switch between them.

The coaxial cable is a nice one...Elco UDC-S (which I got for a bargain price, at least compared to the list price on their website, on a recent Audiogon auction conducted by Andrew from Elco) with custom termination done by Elco (BNC on the DAC1 end, RCA on the other).

I was a bit skeptical that I'd hear a difference between the two...this was supposed to be digital data, after all, so I asked my wife to help me do some blind testing (she was in charge of changing the toggle on the DAC1).

The results? I can hear the difference, barely. And, to my ears, the coaxial sounds better. Better as in clearer, a bit more defined, a bit clearer. Not much...but a little bit. On some songs it's very difficult to tell the difference, but on others (especially electronic stuff with a repetitive set of distinct but distant ambient noises...like the Boards of Canada stuff I tried at one point) it's quite obvious: what sounds like muffled variations in sound on the optical cable sounds like it should on the coaxial, I believe...groups of sounds meant to sound sort of like rain drops.

My headphones for the test were the most detailed and revealing I've ever heard (yes, even compared to the Orpheus + Blue Hawaii combo I've heard on two seperate occasions): Sony Qualia 010 (stock cable, using the DAC1 as amp).

So, there it is...I am now a coaxial cable user, even though I'm connected to a supposedly noisy electrical transport (my computer)...by the way, Benchmark notes very clearly in their manual that the coaxial input is "DC isolated, transformer coupled, current limited, and diode protected." So maybe the argument for a clean optical cable isn't as strong with the DAC1 as it would be with another DAC.

Oops, I should have mentioned the power stuff:

The DAC1 is plugged into a P300 with a Zu Mother power cord.

The P300 is plugged into the wall using a PS Audio Plus power cord.

The computer is plugged into a Monster Power Strip (w/ version 2.0 of whatever their filter thing is called) using a PS Audio Plus power cord.

Also, I should have mentioned that my wife listened to both, and claimed she heard a difference (I asked her what difference, and she said one seemed a little louder than the other...it was the coaxial), but thought it would be too difficult / time consuming to try to tell them apart using a blind test.

There's an interesting postscript to my comparison. About 30 minutes after I finished, I started getting a few drop outs (short, muted sections...one for every minute or so of playback) with the coaxial input on the DAC1. These were visible on the DAC1 because the red error light would flash each time I heard one.

I tried moving my cable around to make sure it had a good connection (and unplugged and re-plugged it a few times) but that didn't help.

I even tried swapping in another (slightly newer) 1212M card I have (for another computer) and this didn't help.

Finally, I tried moving the 1212M to a different PCI slot (despite the fact that I had my computer carefully set up already to eliminate IRQ conflicts and so forth). I picked the last PCI slot relative to the AGP slot (previously it was in the 2nd to last), which on my motherboard (MSI K8N Platinum2) is orange (the other slots are white). According to what I read, the orange coloring meant it is a special slot with higher specifications, originally meant to be used with an add-in comm board for something like wi-fi. Anyway, using this slot seems to have solved the problem (not a single dropout for several hours of listening).

Up until then, my 1212M had been working great for months (on two different motherboards). So, it seems like for coaxial output (vs. optical) the board may have slightly higher electrical requirements?

I am still running with both connections and find myself A/Bing between them from time to time when I'm curious if something I just heard sounds different with the cable I'm not using.

Generally, it's still very hard for me to tell the difference...but there is something there...invariably if I accidentally leave the optical connection on I will "feel' something wrong after a few minutes and find myself switching back to coaxial. Could just be placebo, I know.

I think my optical cable might be a bit damaged (it's pretty beat up from various travels, and I've had it pinched under my computer case a couple of times), so I've ordered another one that is supposed to be really good (according to the lunatics at the audio asylum, at least): Van den Hul OptoCoupler (sounds expensive, but luckily it was not). I'll report the results of my coax/optical A/B tests with it soon.