If you plug in an ALSA-supported USB sound device, then run alsaconf, it won't recognize it.
Steps to Reproduce:
1. plug in a USB sound device supported by ALSA
2. run alsaconf
3. observe that the USB device doesn't show in the list of available devices
recognized the device
I'm using a device (a C-Media chipset) that's supported by the snd-usb-audio driver. I edited /etc/modprobe.d/alsa.conf by hand, and got the device working easily.
This seems strange to me, why and for what you're using alsaconf with usb soundcard, here's citation from debian changelog
«Remove alsaconf entirely. The only valid use-case for alsaconf is
aiding the configuration of ISA sounds cards. However, the common use
people do of this tools is mostly trying it out to see if it "fixes"
their sound, which often makes things worse.»
alsaconf is no longer installed with 1.0.26-r3 and higher wrt bug 456214