usb-audio

Finding the USB device path

1. run udevadm monitor
2. Plugin the device (it's ok to unplug it first).
3. Look for the add events. They'll contain the path of the device when it's plugged in.

Using the USB device path

Set the usb_audio_device variable to the value of the sound card device path found. You may need to set the value of the usb_audio_id variable, too, but its default is likely correct.

udevadm info -p SYS_DEVICE_PATH --attribute-walk will give you a lot of information about the device that can be used to construct udev match rules.