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

@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.