Accuracy of digital data: USB vs. Toslink vs. Coax

Currently I use a Mac MINI as my server and also use it sometimes to stream over Ethernet directly from my modem/router. Currently I’m sending data to my Schiit DAC over USB. I upgraded to a Pangea USB cable because I read that it’s cleaner both from a digital as well as electrical noise standpoint. I can’t identify any noise at this point, but when did that stop me from taking steps just in case there might be noise? I recently saw a YouTube video about how USB cables actually differ from each other in how accurately they transmit digital data. So the question I have is whether converting to optical or coax (my DAC can receive both) would likely carry more “original” digital info into the DAC?

With many DACs you can run a test to verify that the path from the source to the DAC is bit perfect. In almost any working digital system this test will never fail. In other words, even tho you may be able to hear a definite difference between various cables or between TOSLink, AES3, S/PDIF, I2S and/or USB it’s not caused by the data being corrupted. The differences are caused by analog noise transmission on the cable, perhaps by ground loops in the system causing analog noise and/or jitter in the digital stream. All of these effects are very system dependent so using your ears is the only way to know if one setup is better than another.


Thanks Ted. I didn’t realize I was going to get a real reply by an actual Chief digital dude! I would have pretty much come to the same conclusion you did - that the noise is electrical, not digital, and there are ways of dealing with that. But the YouTube video I referenced is where he very logically compared the DIGITAL info of the original file to the DIGITAL info coming out of the end of the USB cable and somewhere, somehow, the 0s and 1s are different, because the DAC is actually PLAYING something when he mathematically cancels the original with the result (it should be total silence). Fortunately there’s no distortion created, only a tiny bump in amplitude it seems, so is that bit-perfect? I guess not, but if there are 5 USB cables between the mic, mixer, master, etc., the end result wouldn’t be bit-perfect either, now would it? I guess the best thing again is to minimize what can be heard, so I’m off to look at USB isolators.

1 Like

I’ve also done the bit perfect test thru USB and all the other interfaces multiple times and always get a bit perfect result for valid configurations, (e.g. sometimes it fails for 176.4kHz or 192kHz thru TOSLink.) His experiment is at odds with my experience. USB is completely reliable for data transfer otherwise we’d have serious problems with USB disk drives, etc. The isosynchronous USB protocol can in theory give errors since it can’t error check if it’s sending real time data, but with valid USB cables, hubs, etc. that’s not a problem in practice. I don’t have the time or inclination to figure out what he did wrong, but you needn’t have different bits to have audible differences with DACs in the circuit.


Hi Ted, thanks for taking the time to type that in. I wonder if that guy ever compared data differences in USB cables with using a dirty stylus on vinyl? I think I’m pretty satisfied that it’s close enough to where there’s no way my ears could discern a difference. As for RF noise, etc., that’s easy enough to minimize - of course there are $800 isolators out there, but the Audioquest Jitterbug for $70 seems to be well-received.

I had one thought: I don’t know the equipment he’s using, but one digital process that changes the data is using ASRC (asynchronous sample rate conversion) which is common in DACs and digital interfaces that remove jitter without changing the output clocks. That would be sensitive to the changes in jitter over the various cables and digital interfaces.


Hi Ted, Getting back to this topic, another question came to mind: If the issue of data LOSS is not really an issue, but the transfer of electrical noise could be, since my DAC can take a Toslink connector, could there be any problem in using a simple $20 USB-to-SPDIF converter like this one on Amazon? Seems to me any possible USB noise from my Mac would be cut off at the pass, so all the connector would deliver is digital data, right? Or is there a rule I haven’t read somewhere that states “No person labeling himself an Audiophile shall ever spend only $20 on anything”? OK, I’ll splurge and buy the $10 cable, too.

Heh, careful J there’s a very deep rabbit hole right in front of you and there’s a very strongly-held belief in the audio community about what the correct answer is: that Toslink is inherently the worst possible interface for audio and nothing can ever change that.

You’re completely correct that the optical fibre eliminates electrical noise from the source and from antenna effects collecting ambient electromagnetic radiation. The major difficulty with Toslink is the way the receiving DAC typically has to derive its clock timing from the light/dark transitions on the fibre. Even though you can decode the data itself with perfect accuracy, there’s a lot of ambiguity about when exactly the clock has ticked and this leads to pretty severe jitter in the DAC. Well, in most DACs.

The DirectStream DAC architecture that Ted designed simply doesn’t have that problem. On those DACs – the original, the Jr and now the MkII – I personally rate the Toslink input as the simplest way to great sound even with cheap sources like the adaptor you mentioned. Not very many people are willing to agree with me though, because on every other DAC Toslink is easily shown to be the worst or sometimes second-worst sounding input.

So yeah, you’d solve for electrical noise but suffer from much higher jitter in your Schiit DAC.

PS: My personal journey with digital hi-fi started 15-odd years ago with the expectation that accurate data was all that was needed, the shock of hearing a comparison between bit-perfect Toslink from a computer vs a modified CD transport using a custom I2S setup, the disappointment of early USB, the hope of asynchronous USB Audio, and then the genius that was the Audiophilleo USB to SPDIF converter. That Audiophilleo was the crucial link until the DirectStream came along and made magic from Toslink.


Hi Antonin… oh wait, different Dvorak. Thanks for the great information. I’ve got some questions. First, what audiophile-related issue DOESN’T involve going down a rabbit hole? Second, so I hear you saying that USB converted to simple Toslink could result in jitter in my DAC, right? What the heck does jitter sound like or do? So I looked up the Audiophilleo USB to SPDIF converter. Look, if I had all the royalties from your grandpa’s New World Symphony recordings, I might buy one of those things, but um, I’m way too cheap to think I’ll notice THAT much less noise coming into my DAC from my Mac. So maybe I should go back to square 2 and stick with good old USB through my Pangea cable. It’s got the right clock-jitter stuff going on, right? Then maybe I go with a good noise reducer like the Audioquest Jitterbug?

Jitter is most of what makes digital sound like digital instead of analog. It’s a lack of focus. It’s edgy and irritating. It’s grime on the window. You can’t describe it in high/mid/low terms because it’s a time-based distortion which impacts all of the signal. A really low-jitter systems sounds… more real. It’s ultra detailed but liquid and smooth at the same time.

Specifically, jitter is the measure of inconsistency in the time between each of your digital samples. Provided you don’t have so much jitter that your digital equipment can’t transfer the correct sequence of bits, jitter only matters in exactly two places: the conversion from analog to digital during recording, and the conversion from digital to analog during playback. Jitter during recording cannot be remediated – your data now contains the error. Jitter during playback is a devilishly hard problem to minimise.

The problem with Toslink for nearly every DAC is that the dimming and brightening of the light gets translated to an on/off electrical signal from which is derived the timing for the D-to-A conversion of each sample retrieved – but the timing of that signal is (in relative terms) abysmally inconsistent. It unavoidably has high jitter.

There are a number of techniques DACs use to try and improve things (eg phase-locked-loops or PLLs) but it’s a percentages game. The less jitter on the input, the less jitter is present on the output, and higher quality sources with less jitter-prone connections (generally I2S > XLR > coax > Toslink) ALWAYS sound better on those DACs. USB direct into the DAC is a different kettle of fish and can be anywhere from best to worst.

If you want to use an external USB converter for your Schiit DAC, try and get the best quality one you can afford and use the hierarchy I just mentioned where Toslink is the last choice. Basically anything with a coaxial SPDIF connection will sound better than the Toslink option because the jitter from Toslink is worse than the electrical noise you’ll get via USB and coax. XLR and I2S have the potential to be much better again if those are options for you.

Extras like the iFi SPDIF purifier can also help reduce both jitter and noise prior to the signal reaching your DAC – provided they’re better than the preceding item in the chain. For instance, I would never put the iFi between an Audiophilleo and a DAC because it’d make the signal worse not better.

It’s also necessary to consider electrical noise on the inputs to the DAC (the big advantage that Toslink has) both for direct effects on the output and also for additional induced jitter the noise can create in the DAC’s clock. But for most DACs, on inputs other than USB, the level of jitter on the input is the #1 concern.

Deep enough for you yet?


Ted likes toslink, at the correct resolutions and good glass, into the DSi and ii.


Hi. Wow, thanks, and yes, deep enough. But also very very well-explained. I probably need to read it a few more times, but for now, I have a great idea: is there any way you could create a “Dvorak’s De-Jittering List” with an ascending order of complexity/expense involved? In other words, start with:

  • Generic laptop > generic USB cable > basic DAC
  • Better quality computer > good quality USB cable > higher-quality DAC
  • Better quality computer > Jitterbug > good quality USB cable > higher-quality DAC (this is where I’m headed)

Of course, this will be YOUR opinion and others will chime in to tell you how idiotic your suggestions are, but it would sure help newbies like me to see a basic trend, experiment with devices, etc. If it would be too much work, I understand completely, but I think it would be a great resource for this forum.

PS: “It’s a lack of focus. It’s edgy and irritating.” - you just described my personality to a T.

Sorry, but that’s just not feasible. There’s so much variation and interaction, and that’s without bringing USB into the mix – which like I mentioned above is a completely different bucket of hurt.

If you want good sound and don’t have a DirectStream DAC, avoid Toslink. For DACs with built-in USB, Asynchronous USB Audio can help a great deal with jitter but USB is the worst for electrical noise, so cable choice matters, the device on the other end matters, and you can benefit from gizmos like a “USB Regen” (now discontinued). For the I2S/XLR/Coaxial inputs, whatever is generating the signal needs to have a really low-jitter clock and high quality implementation, and your cable choice makes a difference.

I hate all that complexity and this is a big part of why I love the DS DACs. In the original and Jr Ted made input jitter basically irrelevant, and in the MkII the galvanic isolation and ground lift options go a long way towards dealing with the electrical noise problem. I want a DAC that makes great sound from any bit-perfect source. There are very few of those, and unfortunately they’re not at the low end of the price scale.


Hey, I understand. I was just hoping for a miracle! Hold on - news update - I got my Schiit DACs mixed up. The first one I had did have COAX, USB and Toslink, but the one I have now is USB only. I guess we can almost never-mind this whole discussion (dope-slapping myself). But good info on the USB noise, etc.

1 Like

Hey, so I just purchased the iFi iPurifier3, which claims it does 3 things at once: Active Noise Cancellation, Re-generation of the USB data, and Re-clocking the data. Everything I’ve read about it seems to point into a good direction for someone who needs (as I do) to stick with regular ol’ USB for data. The one thing I didn’t find, a good thing, is a review saying “don’t bother, waste of time, save your $$.” So now that I have it installed, any suggestions on how best to test it? I thought first, I could simply with nothing playing, turn up my volume so I can hear the hiss I get through the path from computer to DAC, then use the iPurifier and listen at the same volume setting. But then I also wonder whether there could possibly be noise introduced on the line when actually passing data? Are there more electrons being activated by more data? Probably a stupid question, but I’m full of them. Third, is there a type of music or instrument that I should listen to carefully that might show any of these imperfections like noise or jitter? For some reason, I think piano might be a good candidate. I promise to reward your suggestions with the best info I can provide.

1 Like

The electrical noise we’re talking about doesn’t tend to turn up in the same way as analog system noise does. It’s often well outside the audible band anyway. The effects it has are varied, but can include inducing jitter in the operation of your DAC and causing something like (waves hands, shrugs shoulders) intermodulation distortion down into the audible frequencies when you have some signal component close to one of the noise’s fundamental harmonics… I’m honestly not very sure about that.

Jitter itself can’t be heard except for the effect it has on actual signal. What it does is shift some of the signal’s energy slightly ahead or behind of where it should be.

You just need to spend some time listening with and without the iPurifier. If it’s making an improvement, you’ll notice that pianos have more wood and solidity, guitars have richer and more complex harmonics, vocals come from better-defined mouths and chests, cymbals shimmer in greater focus and you’ll hear deeper into any sense of acoustic space. Plus you’ll find yourself more relaxed and engaged with the music, and be able to listen longer with less fatigue.

If it’s a night and day difference you will notice it straight away. If it’s more subtle it’ll take you some time to tune in to what’s happening, after which you’ll be more able to discern those changes in response to other tweaks you make. And the majority of people find it far easier to notice a change that makes things worse compared to a change that makes things better. Swap it in and out and if you’re not hearing anything like that, the iFi device might not be adding much to your system.

1 Like

What you describe with the iPurifier sounds like (no pun intended) what happens when a LAN isolator is used as part of an Ethernet connection. The initial reaction with the LAN isolator may be heard as a reduction in the “presence” of the music – almost like some of the leading edge transients have been softened a bit but I think it’s more like something extraneous has been stripped away and what remains is more natural, life-like. Just my 2¢ naturally.

In particular when our audio club was trying various CD tweaks (green markers, beveling the edges, a mat on the CD, etc.) I was amazed that most made a difference. We were blind testing each and I had a little tinnitus that night, so I voted based on whether my tinnitus was better or worse. I found that I almost always voted with the vinyl enthusiasts and against the digital enthusiasts. My takeaway was that the jitter added a little energy to the music, but jitter adds frequencies that weren’t there in the original music so that added energy in the transients made the music move more for some, detracted from the experience for others and, that night at least, the jitter made me cringe a little and my ears ring. :slight_smile:


@tedsmith I hear the same things you do with my tinnitus and digital audio. I didn’t have this problem with digital audio when I was younger, didn’t get listener fatigue. The better DAC’s nowadays have really lessened this, I haven’t really tried any purifiers or a better modem or switch, something to look forward to.

1 Like

Thanks for the feedback. I’m getting the idea that I don’t fully know what “noise” is here. I kind of assumed it’s “a sound that’s NOT music,” but you seem to be describing it more as “something that does bad things to music.” Operating from my first assumption, last night I sent this to iFi support:

I’m running USB from an Apple iMac. I have a good USB cable (Pangea) connected to a Schiit Lyr DAC/headphone amp, but I run its output to a Convergent Auudio Technology tube pre-amp to PS Audio Stellar M1200 mono-blocks and finally to Vandersteen 2ci speakers. All my cables/interconnects are of good enough quality to not produce noise. I bought the iPurifier3 - USB-B version - to go in between my iMac and Schiit DAC. To hear any line noise at all with everything on, I have to turn the pre-amp up about 2/3 with the Schiit up about half-way. This is much higher than I would ever even think to play music. But I am hearing a slight buzz that I found is coming from a lamp cord running about a foot from the USB/Mac. When I turn off the light, it’s just a light hiss. When I unplug the USB cable with the light still on, no buzz, so it’s not being picked up by the DAC or anything further downstream. It’s either the USB cable or Mac picking it up. Obviously I need to relocate the light, but I am surprised that there is no difference between the USB cable alone vs. with the iPurifier. It seems the noise detection of the iPurifier would notice and cancel the 60 Hz sound coming through the USB cable, right? What am I missing?

Their response: “I am afraid that we cannot diagnose your entire setup due to the multiple points of failure and 3rd party devices.”

Which I think is a cop-out - the point of failure is that the iPurifier isn’t doing anything to the electrical noise on the USB cable. There are no “multiple points of failure” - if I unplug the USB, no buzz - plug it in, whether through the iPurifier or not - buzz.

So is the iPurifier focusing on some other kind of “noise” or what?