Why does USB feature so much in discussions about DACs when the newer HDMI seems better?
I am a bit confused about the frequent mention of USB in the context of stand-alone Digital to Analog Converters (DAC). Why is HDMI left out? Is this a US versus Europe / Asia thing?
The Universal Serial Bus (USB) was introduced in 1996 by a group of computer manufacturers primarily to support plug-and-play for peripherals like keyboards and printers. It has only two signal wires, plus two wires that can supply DC power.
The High-Definition Multimedia Interface (HDMI) was specifically designed by a group of television manufacturers for transmitting digital audio and video in many formats. It hit the shops around 2004. There are 19 pins supporting four shielded twisted pairs, and seven other wires (3 of which can instead form a shielded twisted pair for Ethernet).
I have three universal disk players from Sony, Panasonic and Reavon, which all have two HDMI outputs, one can be dedicated to audio only, the other carries video or video plus audio. (Only the Panasonic does not support SACD). My Marantz AV 8802 pre-processor has 11 HDMI connections and only two USBs.
Of course, both USB and HDMI continue to evolve. Then there is the Media-Oriented System Transport (MOST) bus designed by the automotive industry, which looks even better.
Why is it so?
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. |
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. |
@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 |
@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.
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@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? |
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! |
