Hey Olivier, I assume you are using RELEASE / GENERIC kernel, so
modules / drivers should be already in the system, you need to load
them if they do not auto-load. Then using USB Audio card looks exactly
the same as built-in audio card.
As root execute:
kldload snd_uaudio
This will load the USB Audio module. After that attach USB Audio card
and /dev/dspXX should show up.
If you want this module auto-loaded at boot time put
`snd_uaudio_load="YES"` in `/boot/loader.conf`.
Make sure your card is recognised and supported. See `dmesg` output or
watch first console after connecting the USB Audio card (Ctrl+Alt+F1
to go there from X). If you do not have /dev/dsp despite loaded
`snd_uaudio` try `usbconfig` to see if the card is attached and
visible to the computer among other USB devices. If usb subsystem does
not see the card then audio also won't see the card. In that case you
may want to try different USB port, cable, check if that card works on
another computer / os, etc.
The simplest way to test if sound card works is to `cat /dev/random >
/dev/dspXX` providing the device of interest you should hear random
noise in the speakers. Also make sure with mixer that output is not
muted.
If you haven't read yet there is a Handbook section dedicated to Multimedia:
https://docs.freebsd.org/en/books/handbook/multimedia/
Good luck and have fun! :-)
--
CeDeROM, SQ7MHZ,
http://www.tomek.cedro.info