Yesterday when I needed to watch movie on my computer I couldn't make the sound work. I was connecting my computer with my TV with an HDMI cable. The screen was displayed on the TV but the sound was still comming from the computer.

Setup

• Machine: Lenovo ThinPad SL510
• OS: Ubuntu 13.04 Raring (lsb_release -a)

Wrong solution

I tried installing Additional Drivers, but it didn't find anything.

Rigth solution (for me)

According to an answer on AskUbuntu (and others) I needed to enable radeon on boot.

$ sudo nano /etc/default/grub

The variable GRUB_CMDLINE_LINUX_DEFAULT needs to be changed from "quiet splash" to "quiet splash radeon.audio=1" Afterwards I ran grub update and then rebooted my computer.

$ sudo update-grub

After the reboot I now have two options in sound settings; One for my internal sound card and one for the HDMI. Unfortunately I have to manually select which one to use. It is not toggles automatically when I add/removes the HDMI cable.

IMPORTANT!

The Grub boot loader must be updated this way! See https://help.ubuntu.com/community/Grub2#Configuring_GRUB_2. Do not update the grub files that are auto generated by Grub.