If you have an M-Audio Audiophile 24/96 PCI sound card or anything else
using the "Envy24" chip, be aware: at present neither the GNOME3 "sound"
control panel applet nor the pulseaudio tool "pavucontrol" expose enough of
the card's controls to play any audio. You need to have
alsa-tools-gui installed and use
envy24control to put the relevant sliders
in the right places.