Since version 13.04 I have had a problem with getting sound over HDMI when I plugged the cable from my pc to the tv-set. The problem seems to have mainly afflicted people on ATI Radeon (mine is 4650), so here is the fix:
1) sudo apt-get update
2) sudo gedit /etc/default/grub
3) Change the line GRUB_CMDLINE_LINUX=”” to GRUB_CMDLINE_LINUX=”radeon.audio=1″
4) sudo update-grub
5) Visit the Launchpad website “ALSA Daily builds”
6) Expand the appropriate “Source” (f.i. Saucy if you are on Ubuntu 13.10)
7) Scroll to the bottom of the expanision and download the “Package file” ending in “.deb”
8) Install the file (double-click it and it should open Software Center)
9) Restart the system
10) You now see HDMI under Sound Settings
Let me know if this doesn’t work for you or causes problems.
That’s awesome