Hey Folks, I've managed to get my external audio stable on Big Sur. I found that using a USB DAC (I've tried many of them) would cut out under high CPU load (e.g. transcoding video). Machine is a Mac Pro 2019 so it's not short on CPU or IO resources, and the DAC was always on a dedicated port. Here's the trick I've found: Firewire audio is still fully supported and rock solid in Big Sur. I've run this in two configs, both are stable under high CPU load.
1: Hacking something up with spare parts on hand. I had an old
Behringer FCA202 Firewire400 audio interface, and I hooked this up via the Apple Thunderbolt3 => Thunderbolt 2 adapter, Thunderbolt2 => Firewire800 adapter, and a Firewire800 => Firewire400 cable (yep, I had all these in my bins of cables!). I was surprised that it worked, but it fired right up, no drivers or power adapter required (powered by the Firewire bus). This sounded pretty good, but I wanted to run an outboard DAC, so...
2: Spending $100 to make it nicer. I picked up a
Firewire800 PCIe card from Amazon and a used
Focusrite Saffire PRO 14 on
eBay. Focusrite stopped support for this interface in Catalina, but the drivers and app work just fine in Big Sur so far. This has coax SPDIF output, which is running to my
Schiit Modius DAC. The first setup sounded good, this setup is noticeably better, at least with my higher quality input files.
Hope this helps folks who are struggling with USB audio in Big Sur.