Raspberry Pi 4 sucks for USB audio

I bought a Raspberry Pi 4 B under the impression that it was great for USB audio. It is sold as having hardware issues from previous versions fixed, relating to overlap between ethernet and USB.

However this couldn't be further from the truth! It has a little-known limit on the number of isochronous USB devices. It can run one, maybe two, 24bit 48khz streams before it falls over. Devices with many ports, such as audio interfaces or USB sound cards (e.g. Creative X-Fi HD USB), randomly fail to initialise properly (missing ports, USB errors in dmesg, etc.). I also was not able to get flawless audio out of a Musical Fidelity V90-DAC no matter what I did. You'd think UAC 1 audio would be impossible to mess up after 23 years...

Stick to x86 and/or proper USB implementations for any serious Linux audio work! I pulled out an old J1800 board (fanless x86), added a Renesas USB 3.0 PCI-e card, and all the intermittent audio issues I had been grappling with for months on ARM SBCs vanished instantly.