USB Audio Class 3.0 Support, Intel Icelake Audio Set For Linux 4.17

[phoronix]

Phoronix: USB Audio Class 3.0 Support, Intel Icelake Audio Set For Linux 4.17

Continuing on to with some of what we can look forward to seeing with Linux 4.17 for end-users, the sound driver updates are fairly notable for this upcoming kernel cycle...

http://www.phoronix.com/scan.php?page=news_item&px=Linux-USB-Audio-Class-3.0

[uid313]

How does USB Audio Device Class compare against S/PDIF and HDMI?
Does it support 24-bit audio? 32-bit audio?
Does it support 192 kHz?
How many channels does it support?

[starshipeleven]

How does USB Audio Device Class compare against S/PDIF and HDMI?
Does it support 24-bit audio? 32-bit audio?
Does it support 192 kHz?
How many channels does it support?

See this PDF, page 3 and 4, for tables about UAD 1 and 2 capabilities. http://www.epsglobal.com/downloads/X...io-Class-2.pdf

tl:dr USB is vastly superior to both S/PDIF and HDMI for audio on any metric you want to compare due to relatively large amounts of bandwith it can provide at the very low latencies required for this task. For example a USB 2.0 stream sending to a device using a "high bandwith" endpoint can deal with 15 channels with 32bit-depth at 384 kHz sample rate.
Neither S/PDIF nor HDMI can go anywhere near that as they have less than half the bandwith.

[StefanBruens]

See this PDF, page 3 and 4, for tables about UAD 1 and 2 capabilities. http://www.epsglobal.com/downloads/X...io-Class-2.pdf

tl:dr USB is vastly superior to both S/PDIF and HDMI for audio on any metric you want to compare due to relatively large amounts of bandwith it can provide at the very low latencies required for this task. For example a USB 2.0 stream sending to a device using a "high bandwith" endpoint can deal with 15 channels with 32bit-depth at 384 kHz sample rate.
Neither S/PDIF nor HDMI can go anywhere near that as they have less than half the bandwith.

S/PDIF supports at least 48kHz, 2 channel, 24 bit (+ 8 bit overhead), but dependent on the equipment may do up to 192 kHz. Thats for LPCM, compressed formats like AC/3 and DTS support more.

HDMI 1.0 supports LPCM with 8 channels, 24 bit and 192 kHz, more with compressed formats. HDMI adds 32 channels and 1536 kHz. Thats 37 MBit/s resp. 1.2 GBit/s.

Now to the real differences:

• S/PDIF is completely unidirectional. Format is selected by the source (i.e. 96 kHz will not work with every sink. Depth is not an issue, as samples are always 24 bit (padded))
• S/PDIF has a single sample delay
• S/PDIF has a defined optical interface, avoiding e.g. ground loops
• simple interface, 1 wire pair / fiber

• HDMI audio is unidirectional as well, although the source gets information about the sink using the DDC sidechannel/EDID. There is a limited audio channel in the reverse direction (ARC).
• HDMI audio has a delay of at least on (video) frame, as audio data is interleaved. The actual delay (including postprocessing) should be noted in the EDID.
• complex electrical interface

• UAC is input/output/bidirectional, formats are explicitly set/signaled by the host
• supported formats can be queried from the device
• delay of about 2 USB (micro-)frames, i.e. 2ms/250us. At e.g. 96kHz that is 192/24 samples.
• quite complex implementation, see "1000 kernel lines", that is on top of existing UAC1/2 and USB driver core

These interfaces all have quite different target audiences and use cases, so its almost pointless to do a comparision in terms of better/worse.

[dkasak]

USB Audio Class devices are external 'soundcards', used in professional music setups. These devices typically will have some MIDI interfaces, and various digital line inputs with phantom power ( for powering microphones ). This is *not* a connection to your stereo in the way S/PDIF and HDMI is. It's about connecting high quality audio hardware for recording and live audio work.

[Sniperfox47]

USB Audio Class devices are external 'soundcards', used in professional music setups. These devices typically will have some MIDI interfaces, and various digital line inputs with phantom power ( for powering microphones ). This is *not* a connection to your stereo in the way S/PDIF and HDMI is. It's about connecting high quality audio hardware for recording and live audio work.

Want to correct what appears to be a misconception here. There are tons of consumer devices that use USB Audio Class, not just recording equipment.

From small DACs to get an extra 3.5mm headphone or mic port and bigger DACs for music lovers, to USB headsets for Skype users, gamers, and phone users, to audio docks for your phone. There are tons of consumer level devices that implimentat it. In fact one of the primary focuses for UAC3 was on USB-C headsets and power saving measures for them.

[starshipeleven]

USB Audio Class devices are external 'soundcards', used in professional music setups. These devices typically will have some MIDI interfaces, and various digital line inputs with phantom power ( for powering microphones ). This is *not* a connection to your stereo in the way S/PDIF and HDMI is. It's about connecting high quality audio hardware for recording and live audio work.

I'd want to point out that my ASUS U7 USB soundcard, which works on linux OOTB, can be used for "prosumer" audio recording and such because it has good specs, but isn't a "professional" soundcard by any means. https://www.asus.com/us/Sound-Cards/Xonar_U7/

You can also find smaller USB ones like the U5 (also runs fine on Linux) that are used by people that bought a laptop but can't stand the average laptop total shit sound quality in their relatively quality (not 150$ but not 2$ either) headphones.

Decent Android phones/tablets with USB OTG can also be connected to such external sound cards (support of UAC varies depeding on what device you buy as usual with Android), and devices running Linux-based open firmware like OpenWrt can be connected to such sound cards and become media sinks you can then stream sound to from a mobile device the LAN/wifi.