Sometimes my m-Audio Fasttrack Pro usb soundcard doens't get recognized. That is, it's not listed in the PulseAudio Volume Control, and no sound comes through. However, running
gives me a list in which the soundcard is included.

How can I make the audio system aware of the usb soundcard?

PS: I currently 'solve' it by either rebooting, or keeping plugging and unplugging the usb connection till it's recognized. But this is annoying to do every time.