Comment 29 for bug 864735

Like RoberKH reported, HDMI audio does not work in 14.04 new installation no matter what is done (adding radeon.audio=1 line to /etc/default/grub or using xrandr) though ubuntu documentation states it should work without any modification (https://help.ubuntu.com/community/RadeonDriver#HDMI_Audio). Here are the details:

$ uname -srm
Linux 3.13.0-32-generic x86_64

$ grep -Rn radeon.audio /etc/default/grub
11:GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.audio=1"

$ xrandr --output HDMI-0 --set audio on

$ lspci -v | grep VGA
 Flags: bus master, VGA palette snoop, 66MHz, medium devsel, latency 64
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Caicos [Radeon HD 6450/7450/8450 / R5 230 OEM] (prog-if 00 [VGA controller])

$ xrandr
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
HDMI-0 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 598mm x 336mm
   1920x1080 60.0*+ 50.0 59.9 60.0
   1920x1080i 60.1 50.0 60.0
   1600x1200 60.0
   1680x1050 59.9
   1280x1024 75.0 60.0
   1440x900 59.9
   1280x960 60.0
   1366x768 59.8
   1152x864 75.0
   1280x720 60.0 50.0 59.9
   1024x768 75.1 70.1 60.0
   832x624 74.6
   800x600 72.2 75.0 60.3 56.2
   720x576 50.0
   720x480 60.0 59.9
   640x480 75.0 72.8 66.7 60.0 59.9
   720x400 70.1
DVI-0 disconnected (normal left inverted right x axis y axis)
VGA-0 disconnected (normal left inverted right x axis y axis)