[jeremy205100]

I was wondering which is the better method to use as an output. My MacBook Pro can do both. Does optical have jitter like USB? I read somewhere online that optical will give the best output quality. Will I even notice a difference? I have the DT 990 600 Ohms. I appreciate any feedback, thanks!

 

[Roseval]

Using modern Toslink, you can get very good results.
Like all timed busses, it does have some jitter.
It is possible to improve on it by using a good quality async USB to SPDIF converter.
At least I perceived a subtle difference using a Vlink 192 compared with the Toslink of my iMac.
But the emphasizes is on “subtle”.
 
http://thewelltemperedcomputer.com/Intro/SQ/USB_USB.htm

 

[jeremy205100]

Have you found that the cable length of either of them significantly affects the audio quality?

 

[Roseval]

No, as long as you stay within the limits

 

[eightbitpotion]

Both are digital cables, and both should provide the same quality as long as the DAC is equally as good on both connections.  When using USB you have a pseudo TTL, so if it drops below this boundary it'll simply not work.  Keep in mind that USB 2.0 is rated at 5 meters, so if you go beyond that it'll simply not work (being digital and not analog).
 
Fiber is technically a superior connection, but not how you're thinking.  You can run some fiber for miles (some even 30 miles), but a TOSLINK isn't in that catagory, and all fiber is very brittle, clumsy...etc.  In a nutshel, I don't personally think that optical comes to the audiophile arena with any major benefits by itself.
 
With that said, I have noticed that some DACs sound different with the two different cables (a dac that has both inputs).  I am fairly sure the contributing component here is the variance in the way the DAC handles the inputs....I'm sure some smart DAC or electronics person can jump in here and explain this.  This isn't to say that one sounds superior than the other...just obviously different.  I feel like this is a question that's asked when someone is looking for either a DAC or a source, and it's vital to note that there's not a superior between the two for our purposes; technically they shouldn't be different to us (audiophiles), but some of us put precious gemstones on top of our cables and walls to equalize the harmonic resonance lol...

 

[Roseval]

   I don't personally think that optical comes to the audiophile arena with any major benefits by itself.

What about a perfect galvanic isolation between the PC and the DAC?

 

[linglingjr]

There have been a ton of threads asking the same question.  I've found that it really depends on how well USB or optical is implemented to your DAC.  On some USB sounds *better* than optical and on others it's the opposite.  I don't think there is a black and white yes or no answer.

 

[eightbitpotion]

  What about a perfect galvanic isolation between the PC and the DAC?

It would be relevant in an analog signal, but this is not.  Digital is a completely different breed.  If you've used satellite before you'll know what happens when a digital signal becomes tainted... it looses all integrity and is not recognized/skips.
 
Have you ever witnessed galvanization between a a digital source/path/DAC?

 

[Jd007]

  It would be relevant in an analog signal, but this is not.  Digital is a completely different breed.  If you've used satellite before you'll know what happens when a digital signal becomes tainted... it looses all integrity and is not recognized/skips.
 
Have you ever witnessed galvanization between a a digital source/path/DAC?

you are forgetting the possibility of a ground loop. digital signal connections with the exception of optical/toslink all carry ground, which could form a ground loop, causing humming/noise problems. the only way to prevent this is by having galvanic isolation between the pc and dac, either through using an optical interconnect or a ground isolator (you can find ground isolators for both coax and usb)

 

[eightbitpotion]

  you are forgetting the possibility of a ground loop. digital signal connections with the exception of optical/toslink all carry ground, which could form a ground loop, causing humming/noise problems. the only way to prevent this is by having galvanic isolation between the pc and dac, either through using an optical interconnect or a ground isolator (you can find ground isolators for both coax and usb)

You're right, but I've always been under the impression that the DAC handles the ground loop (if applicable) during the first stage of input.  I suppose that could be totally wrong.  I've never had to deal with that sort of problem because my sound equipment is segregated on it's own power source since other things affect it (like CFL bulbs :-\).  Either way, I agree if ground looping is an issue, then you should add isolation, but this still doesn't make it a pro or con for the whole fiber vs usb since fiber cost significantly more (not just in the cable, but converting all equipment if you need to).  My other comments were based on the assumption that everything is "clean".

 

[Roseval]

You will find Toslink in many audio devices.
Yes, it is cheap.

 

[Jd007]

  You're right, but I've always been under the impression that the DAC handles the ground loop (if applicable) during the first stage of input.  I suppose that could be totally wrong.  I've never had to deal with that sort of problem because my sound equipment is segregated on it's own power source since other things affect it (like CFL bulbs :-\).  Either way, I agree if ground looping is an issue, then you should add isolation, but this still doesn't make it a pro or con for the whole fiber vs usb since fiber cost significantly more (not just in the cable, but converting all equipment if you need to).  My other comments were based on the assumption that everything is "clean".

it actually really depends on your amp's ground implementation. i had an amp that had a ground loop issue (improperly implemented/isolated ground i believe, confirmed to be ground loop issue by using a 3-prong to 2-prong cheater plug on the amp, noise went away) which i have tried with many dacs (including ones with dedicated power supply and ones with battery power), and the ground loop issue is always there with that amp as long as im not using optical. dacs with dedicated power supply and battery did help, the humming noise is considerably lower than ones without (ie drawing power from usb), but the issue is definitely still there and the only way i've found to completely get rid of the noise is by using optical between the pc and dac (admittedly i did not try cutting/taping over the ground and power pins on the usb cable for self-powered dacs, but im not sure if that'll make a difference)
 
when it comes to dacs, it is better to assume that not everything is clean. in fact, i would start assuming that the pc power is not clean as that is more often than not the case. ground loop issue may or may not be an issue, depending on your dac and amp (personally i have not encountered that problem with any of the other amps that i got after), so the benefit of galvanic isolation that optical provides completely depends on your setup (some dacs/amps even have a special ground-lift switch to completely get rid of the problem without resorting to optical).
 
as far as cost is concerned, i think usb and toslink are at pretty much the same level so as to not be a concern for most. a good async usb receiver/controller chip (eg xmos) could cost a lot more than a good toslink DIR. optical cables are also not really more expensive than usb (you can get 3 ft for ~$3-4).
 
to answer OP's question more directly. for playback of materials up to 24/96 (or 24/196 for certain dacs), usb and optical should be effectively the same in quality, provided both use quality components and implemented properly (ie good usb receiver and good optical DIR). usb has the added advantage of supporting much higher bitrates (eg DSD/DXD, but only if your dac supports it), which optical cannot do. usb also provides more consistent playback quality regardless of source device, as the optical output quality of certain devices (eg airport express?) is not as good as others and can cause problems such as massively increased jitter. on the other hand toslink has the benefit of providing complete galvanic isolation, which eliminates any possibility of ground loop issues (if there are any to begin with)
 
TL;DR: if you need super high bitrate playback, or if your optical source is lower quality, use USB. if you have a ground loop issue, use optical. otherwise either should be fine (provided your dac implements both well enough)
 
ps: and if you want DSD but have a ground loop issue? get an usb ground isolator and use usb

 

[jeremy205100]

Thanks for the help guys! The DAC I use now only has USB so I was just curious if one was better than the other. It seems they're both very similar although they each have some unique strengths. 

 

[eightbitpotion]

You will find Toslink in many audio devices.
Yes, it is cheap.

I guess we have different opinions on cheap. If you want to use a cable with an insignificant construction and risk the possibility of it breaking...then yeah a $5 cable will be fine, but if you want to prevent potential breaks and Rayleigh scattering...you can't be cheap about it unless you're literally using a 3' cable that never moves.

A proper cable with proper protection can get really expensive depending on what you need.

 

[RonaldDumsfeld]

Either implementation can give good results but USB is technically superior.
 
The issue with any type of S/P-DIF transfer is that timing information (44.1k) is added back into the digital samples by the clock in the sending device then pumped directly to the actual DAC. With USB the data samples are sent raw and then the timing and conversion are done at the same point. Not only that async DACs (most of them now) have a form of feedback loop that allows the DAC some control over the flow of data. i.e. to prevent buffer over or under runs. If you do not trust the DAC chip in your onboard what makes you think the clock is any better?
 
S/P-DIF transfer was popular at one time with hi fi grade manufacturers because it mimics the operation of CD players. The chips are cheaper and, crucially, it doesn't involve the manufacturer writing or licensing software. That's one of the reasons pro and semi pro audio interfaces represent such good value. They have the software capability in house and have been doing the job longer. For demanding customers too.