Thanks for letting me know that MUSB & DMA is no longer a thing. With that in mind, I finally figured out my problem getting the USB audio to work. Turns out my USB audio device was pulling too much current from the USB port. Beginner's mistake! I finally tried connecting it to a powered USB hub and now it’s working. Should have tried that a long time ago, but I was confused by the mpg123 error messages and the DMA issues others were having when trying to get USB audio to work.
Since I figure this might help others, here are the steps I took to get things working:
I re-flashed the eMMC with ‘bone-eMMC-flasher-ubuntu-18.04.4-console-armhf-2020-03-12-2gb.img’.
It looks like the kernel is “Linux 4.19.94-ti-r36 armv71”.
I installed mpg123 and tested it with an mp3 file. It worked, sending its output to the default HDMI output.
I then plugged in the USB audio device. Sure enough, It shows up when calling ‘aplay -L’.
To set the USB audio to the default audio device, I next created a file called ‘/etc/asound.conf’ with following:
pcm.!default {
type hw
card 1
}
ctl.!default {
type hw
card 1
}
Running ‘alsamixer’ from the command line should now show USB audio as the connected audio device.
Finally, make sure the USB audio device is connected to a powered USB hub and things should work. Before I had the powered hub, I would get the following error when running ‘mpg123 Swish.mp3’ (this is what threw me off for so long):
High Performance MPEG 1.0/2.0/2.5 Audio Player for Layers 1, 2 and 3
version 1.25.10; written and copyright by Michael Hipp and others
free software (LGPL) without any warranty but with best wishes
[?25l
Terminal control enabled, press 'h' for listing of keys and functions.
Playing MPEG stream 1 of 1: Swish.mp3 ...
MPEG 1.0 L III cbr128 48000 mono
[src/libout123/modules/alsa.c:181] error: cannot open device default
[src/libout123/libout123.c:585] error: failed re-opening of device after pause
main: [src/mpg123.c:798] error: Deep trouble! Cannot flush to my output anymore!
[src/libout123/modules/alsa.c:181] error: cannot open device default
[src/libout123/libout123.c:585] error: failed re-opening of device after pause
Anyway, thanks to Robert and everyone else for your help. Audio is a playin!