Why does USB feature so much in discussions about DACs when the newer HDMI seems better?

Most computers have several USB ports, so one is likely to be available for digital audio output. On the other hand, not all computers have HDMI, and the ones I have seen have only one HDMI port, intended for the monitor. All that makes USB a useful input for a DAC.

Of course, some newer DACs are adding HDMI input.

@mike_in_nc 

Yes, that makes sense for computers.  My partner's Dell XPS 13 has so little space for any physical connections, it has an external adapter to support HDMI and Ethernet over USB!

What about separate streaming boxes.  What would be the best connection to a DAC for them?

Do most people stream via computers these days?  The only streaming I use is to check the music out before buying a disk, and I use WiFi (great Australian invention) to connect my mobile to the pre-processor for that.

The best connection is the one supported both by the streamer and by the DAC. Some manufacturers have their own connections (like Auralic’s Lightning Link) or use I2S, and many say that the sound is best if those are used. I have no experience with that.

Leaving aside specialty links, if USB is available, I like to use that, as it supports the widest range of sampling rates. Also, over USB, the DAC controls the clock entirely, without depending on the source. I will say, though, that with the new equipment I’ve tried recently, I cannot hear any difference between USB and SPDIF or AES3.

@richardbrand 

Why is it so?

You'll have to talk to the Accountants, then Marketing, Then the Lawyers who must grease the palms of the proper officials who will make sure they have  your complete cooperation with the proper authorities who will keep your competitors off your case should one arise.

USB is a terrible interface to a dac. Ethernet is better and i2s is even better. Most won’t know this because they buy cheap stuff and the cheaper stuff doesn’t include Ethernet or i2s. For a decade, all your high end manufacturers provided a proprietary link from their space player into their preamp or integrated or possibly a dac. They used hdmi/i2s for this. I use a streamer that doesn’t even include usb out, only i2s into my dac

It depends on the manufacturer in my experience. I have a Holo Audio Cyan 2 DAC.  It has multiple inputs.  Holo makes a Red streamer which connects through i2S which is tailored to connect between the two units.  I didn’t like the Red and the apps I needed to use.  I went with a Innuos Zen Mk3 streamer instead which only connects using USB.  It sounds excellent in my system.  Would i2S sound better- possibly if I could even tell the difference with my old guy ears.  I love the Sense app that Innuos uses, even better than the BluOs app which was my previous favorite.  I only use HDMI connections with my TVs.  So many connections and so many different cables.   Pick what sounds good to you in your system.  

Glass Toslink likely better than cables. No interferences. 

@vinylshadow - Toslink, whether glass or some kind of plastic, is THE worst thing to use for audio connections. It's been slagged off for decades, since it was first used for audio in fact, for having terrible sound quality. Obviously opinions will vary, but it totally depends of the resolution of the system - if you have a poor/low quality system, it probably sounds OK.

@daveteauk  I guess so....I was going off the P-Link glass optical cable that Playback Designs uses to connect their streamer to their DAC. That cannot be beat by any cable. 

I would like to find an HDMI splitter, that I can use to feed audio into my dac and have the simultaneous video be fed into my av processor. I’d like to be able to bypass the dac in my processor and maybe I can get it to sound better.

Although, maybe it won’t sound better because my processor is very good. Would love the flexibility to pursue other dac options.

@emergingsoul

All of my recently purchased silver disk spinners support two HDMI connections, from the very cheap Sony transport (A$250 or so) and up, I guess for exactly this reason. In my case, the lauded Texas Instruments Burr Brown DACs in my Reavon player turned out to be far worse than the eight 2-channel AKM DACs in my AV pre-processor.

I would encourage you to read the specification sheets of any DAC chipset you are considering. For me, it is very important that they natively support Direct Stream Digital (DSD) which I guess rules out R2R. If the specification sheet does not mention DSD, you can bet your top dollar the DAC does not support DSD.

I note in passing that DSD can be mathematically converted to multi-bit without interpolation, but multi-bit needs interpolation (guesses) to go the other way.

@richardbrand - can't say for sure, but I'd guess that most people who stream do it from their phones.... 

@emergingsoul maybe this. I have one I’ve used just for digital audio output and worked well.

https://a.co/d/fGmgPpQ

@rbstehno 

How do you figure?  USB is almost always bit-perfect.  When it's not, due to something being horribly wrong, you would definitely hear clicks and pops.  High end USB cables are snake oil, and there is nothing wrong with USB in general.

I don’t reply to cable naysayers, if you can’t hear a difference between cables, no sense talking anything audio to you.

I used to stream from my Mac mini using the headphone out into an adapter for optical. But your limited to 96khz 24 bit. With an external streamer/dac like auralic, you can stream much higher resolution with less noise from a computer. 192khz/24bit and 512 dsd. No usb connection, all Ethernet for streaming or wireless and balanced output.

My take: Audio Video HDMI is only available within the video world.  BluRay players that can play SACDs works only with Home Theater receivers that can decode DSD. I only have experience with SAME BRANDED BluRay and HT Receivers. Not sure how well it works with mixing brands.

To make it more confusing, then there are SACD players that use HDMI (that is I2S, but uses HDMI cables, no video involved) that can be connected to external DSD capable DAC using I2S via HDMI cable.  It can be a bit complicated as I2S pin outs are NOT standardized. So caveat emptor

I2S was designed for audio. Toslink was a cheap way to send digital signals developed by Toshiba. USB was for data not audio. When you look at it from a cost and convenience factor and take into consideration what technology was available at the time, one can see higher end audio components are using I2S because it’s better engineering and better sound today. Of course anyone is free to use whatever connector that might have and if it sounds fine for them…. no worries. Paul McGowan of PS Audio explains these differences pretty well in his informative YouTube videos.

Navigating the depths of digital ignorance calls for a strong submarine.

@2psyop   Thanks to you, I am enjoying Paul McGowan on YouTube.  Straight to the point and authoritative.  I particularly like his comparison between DSD and PCM - probably because his assessment and mine agree!

My understanding is that I2S is a two-channel Pulse Code Modulated interface designed by Philips to connect integrated circuits on a board, and dates way back to 1986. There is no agreed cabling standard.

For those who believe that USB covers a lot of audio standards, here is an extract from Wikipedia on HDMI audio:

"If an HDMI device has audio, it is required to implement the baseline format: stereo (uncompressed) PCM. Other formats are optional, with HDMI allowing up to 8 channels of uncompressed audio at sample sizes of 16 bits, 20 bits, or 24 bits, with sample rates of 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, or 192 kHz.^[5]: §7 HDMI also carries any IEC 61937-compliant compressed audio stream, such as Dolby Digital and DTS, and up to 8 channels of one-bit DSD audio (used on Super Audio CDs) at rates up to four times that of Super Audio CD.^[5]: §7 With version 1.3, HDMI allows lossless compressed audio streams Dolby TrueHD and DTS-HD Master Audio.^[5]: §7 "

I'd just add that Dolby Atmos is supported, with up to 32 channels.  There is a licencing cost for HDMI which may put smaller manufacturers off using it.  There is also great confusion over the theoretical capabilities each version of HDMI specifies, and the actual capabilities that are implemented by the component manufacturer.  They are supposed to list the actual capabilities, which as @devinplombier says, plumbs "the depths of digital igorance" for consumers

@rbstehno what is wrong with USB? Is external hard drive losing bits?

@2psyop how audio file is different from Excel spreadsheet. What is special in 'audio' bit packets over Internet.

@2psyop  the only thing Paul McGowan doesn't say is that I2S was never designed to be transmitted over a cable from one component to another.

Good DACs take USB and galvanically isolate it from the input section, thus eliminating most of the electrical noise that it might otherwise carry, hence USB can (in all but the cheap stuff) be a very good input, even from terribly electrically noisy computers.  In the last few years I2S has made a splash because of companies like PS Audio developing their own "standard" for the pin outs and many other companies have unofficially adopted that same "standard" so they can play well together without the end users being a geek.

I2S has the "claim to fame" that it separates out the clock signal from the data stream and in theory that can allow less jitter and noise.

Note that I2S existed inside digital devices long ago well before HDMI came along. They are just implementing I2S via an HDMI connector now because those were available, relatively cheap, and semi understood by the masses as a "cool connector".

None of my devices so far have an I2S connection so I use USB (instead of coax or Toslink optical). Toslink optical might have been a great digital connection if glass were used instead of plastic and if they had upgraded it to be more robust in bandwidth, but it never was, hence the limitations make it the "worse" connection you can use at least if you are trying anything better than CD Redbook quality bit depths and sample rates.

I’ll take it on word of mouth that in $$$ systems, I2S can often sound better. Overall, it isn’t something I’d worry about. The DAC you choose, speakers, amp, and your room are liable to make a bigger difference in sound quality.

Note, it may be years before "slow as molasses" industry governing boards like the IEEE and their audio steering committees to create or adopt a "real" I2S standard. 

Most streamers don’t have I2S outputs hdmi 

If you have a DDC Reclocker then they have I2S outputs  

the only brand I know that sell true I2S  audio cables without the video wires is the Excellent Tubulus Audio cables.

@2psyop "USB was for data not audio." Sending audio DATA over USB *is* sending data, zero and ones. Digital data transmission does not depend on what type of data it is. Data is data from a transmission perspective.

HDMI isn't really the correct terminology for audio only use. Yes, the connectors are HDMI, the cable itself needs only be I2S, this means only 8 pins actually wired, the rest are superfluous for audio only. Plenty of nice audio only I2s cables out there today, Tubulus and Audiolund are a couple manufacturers.

I2S has a couple advantages over usb in that data and clock runs are segregated, usb has to extract data from clock run. The other advantage is I2S is native signal path within dacs, usb inputs converted to I2S. Having said that manufacturers have gone to great lengths optimizing usb at both the streamer and dac, so usb can be very nice interface these days. Theoretically, I2S imputs on dacs shouldn't require as much work as usb, still clock and power supply to that clock should be optimized. I2S is virtually unknown output on streamers, and if included not likely to be optimized. So now we come to the greatest liability of I2S, that being not designed to be sent over cable, clock should be located in closest proximity to I2S circuit within dac. For this reason best to limit I2S cable length to .5M or shorter, using such a short cable could be problematic for many due to equipment positioning issues.

And then we have the question of optimization in the implementation of usb and I2S, such that a well implemented usb would likely better less than optimized I2S. Top of pyramid would be quality implemented OXCO clocking on either of these interfaces, this mean quality clock and power supply to that clock. Next would be TXCO, then Femto, this hiearchy not set in stone, therefore, quality implemented TXCO or even Femto could better less than optimal OXCO.

Bottom line, so many variables, individual setups could favor usb or I2S. In my case I've come to the determination I2S superior to usb since I have both well implemented usb and I2S to choose from, I2S beats out usb. I also maintain I2S inherently superior to usb based on reasoning explained above, this as long as I2S cable length .5M or less.

'Experts' have a variety of opinions in this matter, some refuse to offer I2S dac inputs based on a particular mindset, others offer them based on another set of reasoning. No one I'm aware of offers optimal I2S input in dac, OXCO clocks with high quality power supplies simply take up too much real estate to offer in dacs. Optimal I2S rarely if ever offered on streamers either, usb seems to be their de facto output, sometimes network. This is where ddc come in, they take what is hopefully optimized usb out of streamer, convert to quality I2S that is synced or slaved to dac, this means one is using clock and power supply from ddc vs dac internal clock and power supply. There are a small number of custom streamers such as mine able to directly output well implemented I2S to dac, this means bypassing usb altogether, this may be superior solution.

Finally we have the proprietary interfaces like the ones in Auralic, Taiko,etc. based on reviews these surpass both usb and I2S.

Here I am quoting from a respected DAC designer:

OK...see if this makes any sense to you: if clocking gets corrupted with a single channel traveling on one wire then how would it make any sense to attempt to coordinate three separate clocks on three separate wires?

It makes no sense.

If I2S was actually better they would be using it in recording studios and they most certainly do not.

If I2S was actually better then nearly every company in the audiophile industry would be promoting it and they most certainly do not.

There are a small group of Chi-Fi manufactures who started promoting I2S and the audio-fools bought into it hook-line-and-sinker.

If I2S sounds better in a specific DAC it is only because the other digital inputs on that DAC are lacking, not because I2S is inherently better.

The above excerpt is from pg 7 of this excellent thread.

Really, it is puzzling to see audiophiles bicker over various types of digital connections that are either deprecated (spdif/toslink/coax), never meant to operate over cable (I2S), or that can be made to work well by jumping through a thousand hoops (USB).

By the way, why are audiophiles still stuck in USB 2.x? The 3.x revision has nine wires (vs. 4), enough to carry more clocks than a train station if that's what you think will help sound quality. 

Meanwhile, AoIP - Audio over IP - is a thing, and has been for years. Runs flawlessly over standard RJ-45 or better yet, SFP. Dante and Ravenna are well known AoIP implementations popular in pro audio. But to my limited knowledge there has been a grand total of one Ravenna-enabled audiophile DAC. Why?

@devinplombier - very, very few people understand how digital interfaces work. It is easier to understand spdif/toslink with all its jitter and whatnot, but explain USB or Ethernet... good luck. I often feel people believe there is an actual "stream" of bits between Tidal server and their device...

@sns HDMI natively supports pure audio - have a look at my earlier post where I list what it can do.  It is a very impressive list, certainly way beyond I2S.

Now, HDMI connectors are attractive for other uses.  I have a camera system in my motorhome which supports four analogue TV cameras feeding a single display. Dometic, who makes this system, choose to use HDMI connectors to carry the analogue TV signals.  Despite there being a standard HDMI connector for in-vehicle use, Dometic use the totally unsuitable consumer connector!  Hopeless.

I had never heard of I2S when I started this thread, but I can understand how HDMI with its 19 connection pins would provide an easily available way to transmit four signals.  But it certainly is not native HDMI.  There are 10s of billions of HDMI connectors in the world today.

@devinplombier I am equally staggered! 

You did not mention the latest incarnation of USB which has a connection count of 24 wires!  The connection topography is shared with several other technologies including Thunderbolt!

The naming and description of this latest USB evolution (revolution?) is confusing in the extreme.

My understanding is that for use of the latest features, the cable itself needs to be active.  That is, it has to have embedded logic chips.  That's how it can carry HDMI, which itself can carry Ethernet.

@mikhailark Absolutely spot on!  On another forum, an audiophile claimed there could be no difference audible between CAT5 and CAT6 Ethernet cabling, because audio frequencies are much lower than Ethernet transmission rates.  Anyone who does not get the point, does not understand how audio is carried over packet switched networks.

By the way, Ethernet on its own does not guarantee that a packet will actually be delivered, nor does it guarantee how long it may take to transmit a packet.  To probe why, take a trip to the Hawaiian Islands and try to understand the ALOHA radio data system which was the genesis of Ethernet.  The secret is in the CSMA/CD acronym - Carrier Sense, Multiple Access / Collision Detection.

The internet is also packet switched technology, which is evolving mainly through Requests For Comment!  Audio over IP (Internet Protocol) uses packetisation, whatever the physical wire arranement.

SNS

You've nailed it perfectly. There are SO many reasons to use I2S if you can, and you explained it really well. I agree that short HDMI cables are best, but I've had excellent results with the Audioquest Vodka 48 8k/10k cable at 1 meter. For small budgets, the Supra 2.1 HDMI works really well as does the Audioquest Cinammon HDMI.....but those needed to be shorter than 1 meter for best results

It is true that there is no standard for I2S pinouts, but I've never had a problem with Supra or Audioquest. Also many DACS provide pinout configuration, I know that Denafrips does in all of their DACS.

The other benefits can be true of DDCs too, as it allows for: better quality clocks, galvanic isolation, optical isolation, separating the data and clock signals, and of course keeping the I2S signal in tact from the DDC through the DAC.....with no further conversion until the Digital to analog conversion in the DAC

@sns, @vthokie83

Good explanation of USB versus I2S, but nothing about the native audio capabilities of HDMI!  Remember, HDMI handles multiple audio channels at breathtaking rates and these days includes an Ethernet channel to boot.

I am starting to question why audiophiles don't advocate for mono over 2-channel stereo.  How many backward steps can be taken?

richardbrand

That's true, I did not....and I do understand your point. I'm not an electrical engineer (I'm mechanical) nor a builder of audiophile equipment. I was responding to the various USB/I2S/SPDIF/Toslink posts in between, and reflecting on my own personal experience with my system

@vthokie83 

No worries!  When I started this thread, I was mystified why USB was so prevalent when there is a purpose designed, point-to-point solution for high-bandwidth multi-channel audio in the form of HDMI, which is ubiquitous in modern TVs and Audio Visual gear.  I never expected anybody to mention 'legacy' formats like SPDIF or Toslink  and I had never even heard of I2S.  It seems that the inventor of extending I2S over cable is only interested in 2-channel audio.

I remember the fuss that arose over the introduction of 2-channel stereo when mono had been the only option.  It was going to practically double the cost of HiFi for goodness sake.  Now I am wondering if there is a similar reluctance to move to multi-channel audio, for a similar reason.  Multi-channel high-definition audio has been available on SACD for over 25 years now.

For what it is worth, I have an 8.1 system with no center channel.  The main front speakers are better quality than the rest!  Generally, the rear speakers carry ambient sounds from SACD but some recordings on Blu-ray have Atmos and use all my speakers for truly immersive sound.

Oh, that recommendation to keep HDMI cables short only applies when they are not carrying native HDMI signals!