Digital Interface Nervosa (USB, I2S, SPDIF, TOSLINK, AES, DDC, WTF, BBQ)

Creating this thread as a place to keep general discussions about digital interface nervosa … especially those that stray from the main purpose of the threads they originate in …


I was just going through this and I was curious to know if there is a thread or discussion about the best connection to a dac. Optical, coaxial, or usb. I think now some dacs come with gen3 usb and that larger 9 pin connection. Wonder if audio will gain benefits from that, but probably just speed. But that’s not the info I seek, just a thought

Which connection works best depends on both the DAC and what’s feeding it. There’s no, single, “this is the best connection” choice here. Pros and cons for all of them.

Most of the differences come down to how electrically clean your source is, where/who owns the sample clock, and what formats you need to support.

So, even for a single specific DAC, which input is “best” still depends on the source that’s driving it.

USB 3 in audio means a variety of things - pretty much none of which are qualitative.

Most DACs with a USB 3 connection are still using older USB protocols, and the ones that aren’t are generally professional studio gear. Also, the UAC 3.0 (USB Audio Class 3.0) standard is more about power management (reduction) and device-feature discoverability/configuration than it is about quality. UAC 3.0 still has the same 24/384 spec as UAC 2.0.


Personally, I’ve gotten tired of researching how each dac does with the USB input so I just purchased a DDC to take that part out of the equation. Plenty of people say USB is “good enough” but it’s hard to know if it’ll be “good enough” for me.

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So I had to look up DDC. Search here shows Digital to Digital Converter. Won’t that still have the same set of issues? You are converting SOMETHING to what, Optical? To avoid an electrical USB connection. But how does the DDC connect? Are there any conversion issues? Bit-perfect questions? Who owns the clock? Limitations on sample rate and bit depth?

These are, by the way, genuine questions, as I’ve never used such a device, but have heard some say that even with my Bifrost 2, optical may be better. Not sure I would actually hear a difference, but my mind is open (so the glue inside can dry).

Potentially - it depends on the implementation, how it is used and, of course, the system it is used in (there are no free lunches, after all). It does, however, provide an alternative means of getting your digital source signal into your DAC which may, or may not be beneficial depending both on your DAC, source and the DDC in question.

If you invest in a good DDC, with proper isolation, excellent clocks/clock stability, no power/noise issues, then the benefits tend to be realizable across DACs. Not necessarily ALL DACs of course … nothing stops a DAC design putting a better USB->I2S* implementation in their own box than the DDC you happen to be using

For example, prior to the Unison interface, Schiit’s Yggdrasil generally sounded better driven via AES than it did via USB. USB Gen 5 muddied that somewhat, depending on source system. So a good DDC (e.g. a Mutec unit or a Singxer SU-1) could let you use a source with only USB as an output option with the AES input on Yggdrasil.

Similarly, the original versions of the Holo Audio Spring DAC sounded best driven via I2S. A DDC (or suitable transport) is necessary to use that interface.

Bifrost 2? If you have ground-loop issues it may make a difference vs. the native Unison interface, but that’d be dependent on the quality of the TOSLINK implementation, and cable, AND DDC vs. the already excellent Unison input. You’d be looking at spending $400 or so on the DDC and another $100 on a proper Lifatec TOSLINK cable to get something that had any chance of being equal.

*Interally, DACs generally use I2S for data transfer … specifically the DAC chips.


If I may contribute 2 cents worth on Unison USB, I am of the recent opinion that it may negate the need for any external USB de-crappifier, or arguably even a DDC. I have owned three Schiit audio amps with internal DACs without Unison USB: Jotunheim, an early Modi, and a Ragnarok 2. I noticed very low level noise with those that I could only attribute to interference with the USB. It stopped when the USB cable was pulled out. Mind you it was low level but it was not my imagination. I have been enjoying a brand new Modi 3+ with Unison USB and it is dead silent, with the same cable and the same MacMini source. I have also read many comments here how good the BF2 is with Unison USB.

All that said to suggest that Unison USB may solve some or all of what a DDC would be needed for.

And that the Modi 3+ is really, really good!


Basically the DDC will take USB and output in a different digital signal (AES, Coax, toslink, i2s). I believe the DDC will own the clock and most DDCs are converting USB to something else so the limitation in sample rate and bit depth shouldn’t be an issue.

I think Torq brings up the unison USB which many people believe to be great and even better than the Ygg’s AES inputs but that is certainly not the case with all DACs. Based on my observation, USB has been a terrible way to transfer audio and it gets a bit old having to see if people have compared the USB input to the other inputs. But like torq mentioned, not all DDCs are created equal and some DACs might not benefit as much (either cause all their inputs suck or their USB is done well like what people say about the Ygg).

If you look at the pro audio scene, separate devices for clocks are all over the place. I think it’s still an unusual thing in the headphone world.


Do you mind sharing what is the DDC you’ve got?

So now that’s fine, I am very new to quality audio. So I’m doing a lot of research. I’ve been really dedicated to audio, no work since the beginning of the pandemic. I listen to and have headphones on almost 8 10 hours a day. Usually used to listen like an hour or so.

So my interest has peaked in getting to know more.

First, I see that some people say using a lap top is a better source for audio because it does not feed directly off the power grid and directly off of the internal battery. Not sure how much truth is behind it, it does seem to have some validity based on the concept. So I was wondering your thoughts on that.

Second, I recall looking into and now more so about network streamers. I watch Hans Beekhuyzen and he preaches about the SoTM. That the streamer, don’t quote me just saying, that it kind of works like a chord m scaler. I am probably totally wrong about this, but it does the clocking prior to sending to your external dac and has influence on the sound. Even via usb has a drastic effect on sound quality. It will greatly improve the dac which you already have. Wondering what your or anyone with experience having network players.

I think this goes hand in hand with the laptop question. The network player is electronically cleaner than going straight out of a desktop pc.

But yea this improvements to your existing dac got me thinking this maybe a good investment. Unfortunately with no work I am on a tight budget, so I’m just trying to see what makes most sense.

I build PCs for myself, and I’ve seen some people DIY a simple pc strictly as a Roon endpoint. Not sure if I can put together something as clean as network player. That may take much more knowledge or does it?

Honestly I would buy a network player straight out, but then I see most require Roon and the Roon subscription is clearly added cost which has me hesitating.

Just my thinking, just more focused on a response regarding the benefits and is worth it to my two questions above. A laptop is far more easily attainable, but is the benefit there

In general, there’s FAR more electronic noise and hash generated inside a laptop than there is coming from its external power supply. So you might eliminate one extra source of it (the external PSU), but the primary issues would remain.

If you really want guaranteed isolation from potential electrical/noise issues (most of which are more theoretical than actual when it comes to measured/audible output at the DAC), then run TOSLINK from your source.

A streamer is a device that takes audio from some network-based protocol and turns it into a digital output suitable for feeding a DAC. A streamer may, or may not, include a DAC. But in the purest terms it’s just the part that takes a network audio protocol and provides a conventional digital output to a DAC (USB, S/PDIF, I2S).

Chord’s M-Scalers are NOT streamers. They perform high-order upsampling (2048 fs), in two stages, and the apply proprietary filtering to the result using million-tap filters*.

SotM’s devices are NOT M-Scalers. They may have upsampling features, but unless using them with the NAA mode with HQPlayer and it’s upscaling and filtering capabilities (which require SERIOUS processing power), they’re not doing anything like what the M-Scalers do.

Lots of devices do re-clocking. Unless it’s feeding an S/PDIF or AES3 interface, or a direct Word-Clock input, it has no effect on the DAC’s sample clock or jitter.

As for drastic effects on sound quality … not in my experience nor measurements. “Some” effect, in some cases, yes. Worthwhile, even … again in certain cases. But it is by NO means an across the board benefit, or even always a benefit at all.


A surprisingly large number of “Network Players”, especially some of the more expensive ones, are just ITX-based mini-PCs in a fancy chassis with some customized software on top. So they have ALL the downsides of a conventional PC … perhaps excepting the super-noisy/power-hungry overhead of modern graphics cards (since they invariably run integrated graphics solutions and don’t actually use those).

Buy a DAC that can take an S/PDIF, or better yet AES3**, input, and then build a Pi2AES-based streamer. Will run you a couple of hours and maybe $300 or so. Beyond that, you’re into true, specialty, streamers (not half-assed, over-priced, warmed-over ITX PC-based “high end streamer” units).

Digital interfaces, power-supplies, cabling, software tweaks and so on are things you shouldn’t be thinking about right now. They are “last few %” improvements even in the BEST of systems. You need to figure out your headphones, amp and, most notably at the moment, your DAC.

*Filter tap length relates directly to the sample rate of the audio being processed. Higher sample rates require longer tap lengths. If you used a million-tap filter on normal-rate 16/44.1 data you’d be wasting >999,900 of those taps.
**AES3 is, for the most part, the same as S/PDIF. There are differences, but in consumer gear “AES” is just a balanced transmission line instead of a COAX or TOSLINK connection, using the same signaling protocol, at double the voltage of COAX (since it’s differential) with a couple of status bits set differently in the frame data.


I took a leap of faith and got the Denafrips Hermes DDC. It’s in the middle of the lineup and I decided to try it because 1) I don’t see a lot of DDCs using a OXCO, 2) while some people don’t like denafrips, I think they’ve been doing some cool stuff like how the Gaia and Term+ work together, 3) it was at a price point that I was comfortable with.

I don’t know if it’ll be a huge improvement or not but it’s part of the fun of this hobby I think. If it doesn’t do anything for my system, I can probably sell for basically 90% of retail (which is the going rate for denafrips products used). If it does do something, I might consider grabbing a Denafrips DAC to pair with it since it does have a i2s output.

One thing I did consider but didn’t get was a Metrum Adagio as a DAC. One thing to keep in mind is if you decide to go the i2s route, there are multiple pinouts for them so I would’ve had to recabled an ethernet cable so that the pins will go out of the DDC into the right spots for the DAC. Generally if you buy a DDC and DAC from the same brand, their i2s pins will match up.

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And this thread is why I bought a pi2aes.


Well, as of today, my streamer is an old (discontinued) Chromecast audio with a digital out to a DAC. That’s probably the closest thing to bit perfect I have, even though I suspect that little thing resamples everything to 48kHz.

As far as of DDC, I’d do using regular optical Toslink cables. Already have a cheap’o FiiO K3 doing that actually. Since I only use Youtube music service, I guess I’m probably 90% there (or more). I still see a lot of gear using that format so it should be a fairly inexpensive system to build.

YMMV, as usual. Cheers.

Hear it for Pi2AES! I’ve used a variety of network players, some costing > 5x a Pi2AES-based assembly, with not shabby DACs (Soekris dac1541, Metrum Onyx, Schiit Yggdrasil, Sonnet Morpheus, Holo Spring 2 KTE), amps (SPL Phonitor XE, Eddie Current Aficionado, ecp DSHA-3F, Apex Peak), and headphones (Dan Clark Audio Ether C Flow, ZMF Verité open and closed). Pi2AES is as good or better with the above gear than any previous network player I’ve used, which is really embarrassing for other network player makers: a good designer working out of his garage in New England puts fancy nameplates to shame. No hype, no snakeoil, just honest engineering.


From my understanding, the pi2aes is a standalone streamer. Is there a way for me to connect it to my PC when I want to use my system for other audio stuff or do people just change the input?

You can run different software with a Raspberry Pi, the Pi2AES is just a board that plugs onto the Pi extension socket. For instance, I use RopieeeXL on one on my Pi2AES-based systems, which allows me to stream Airplay from my iPad or Mac to the Pi2AES, as well as Roon, which is the main use. It also works with UPnP/DLNA and Spotify (I use neither). Other software such as Volumio or Moode has different capabilities. The only negative of the Pi2AES, for some users, is that it requires some hardware and software assembly. But I don’t know of any turnkey network player under $2K that is better or more versatile. Maybe @Torq knows?

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Depends on how you mean “connect to”. Several wireless protocols work with different versions of the operating systems you can choose from to run on your pi.

As far as a direct usb into aes converter, no this would not do that.

This might:

Yes I agree, I just got the Geshelli labs Jnog, and I actually really like it. I have no experience with multiple dacs, I have an ifi Nano BL which a buddy of mine who got me into headphones let me borrow. This is the first dac I’ve ever purchased.

The JNOG does have usb, but for some odd reason there’s a tick in my headphones when I use the USB. A random tick every 5-10 seconds and it comes out of my right or left channel. Kind of sounds like it’s coming from the 10 11 o clock position of the headphones.

I tried a bunch of things, switched from XLR to RCA and it still had the tick. I tried a different usb cable and it is still present. Not sure what it is or why I reached out to Geshelli and I guess the head hancho will reach out.

Point being I had to use toslink, my pc has toslink but it never worked, I watched and read about the fact you have to enable it. My pc is brand new, and it wasn’t enabled so therefore it wasn’t working.

But after using it I really like it. Not sure if it’s the JNOG, but I am aware it kills off emi and rfi interferences. The usb was great too minus the tick.

That’s why I was like if a network streamer could improve my dac that would be amazing

The last thing I can think of that might cause this is excessive DPC Latency.

I know you have a fast PC, but even the fastest machines one can build can (think 64 cores, >1.5TB of RAM etc.), and DO, run into this as it is not specifically about how much CPU capacity or memory you have. It can happen as a result of a single problematic driver, or even device loading sequence, and it’s quite common on “gaming rigs” due to all the extra crap they tend to run.

Take a look at this article and work through the steps. It’s not for your DAC specifically, but the general approach is the same for all.

Network streamers may, or may not, result in improvements in DAC performance. There are no guarantees. But unless you want streaming access for it’s own sake (e.g. running Roon and wanting an end-point where you don’t have/want a computer) then I wouldn’t do it for a $200 DAC. Adding a $300 streaming solution won’t turn that DAC into a $500 DAC. You’d be better off spending the combined sum on a better DAC.

You’re better off fixing your USB issues first anyway.