To support DD+ and DTS-HD HR ; your audio card must support stereo output at 192kHz.
Audio/Video cards known to support it:
ION and 9400M IGP : provided you use a kernel newer than 2.6.32 (it is not supported in kernel 2.6.31 and earlier)
Some Intel HDMI graphics chipsets (in particular IbexPeak (0x80862804), CougarPoint)
Audio/Video cards known not to support it:
Most ATI card (many only support 48kHz)
Intel HDMI graphics chipsets Cantiga, Eaglelake
To check for actual support, run mythfrontend and go into Setup -> Audio. If the E-AC3/DTS-HD flag is enabled, it is likely that your audio card supports it. Remember you must use an HDMI connection. Optical or coaxial SPDIF will *not* work.
TrueHD and DTS-HD MA support
For your audio card to support loss-less HD audio passthrough (TrueHD and DTS-HD MA), your audio card has to support HBR.
You can check DTS-HD/TrueHD support on Linux by checking for "HBR" text in "Pincap" line in /proc/asound/cardX/codec#Y. This doesn't guarantee in any way that your audio card will support HBR ; but if you don't have it, it's very unlikely that it does.
Chips known to support HBR:
Chips known not to support HBR:
ION first generation
nVidia 9400M IGP
nVidia GT2xx (*)
nVidia 8xxx, 9xxx
(*) Though not officially supported, HBR works to some extent with nVidia GT2xx ; your mileage may vary. It is highly dependent of the combination between audio processor/amplifier and video card.
You'll need a recent linux kernel (>= 2.6.36) that contains the required ALSA drivers (>= 1.0.24. Version can be found in /proc/asound/version).
Alternatively, Ubuntu users can grab the latest backported drivers from the daily ASLA ppa
Or the latest ALSA drivers can be compiled from the git repository
git clone git://git.alsa-project.org/alsa-driver.git
git clone git://git.alsa-project.org/alsa-kmirror.git
sudo make install
Alsa library 1.0.23 is the required minimum. However if you had to mess with the device name to get basic audio working, it is strongly recommended you get a new version as otherwise you will likely have to mess with alsa configuration file.
git clone git://git.alsa-project.org/alsa-lib.git
sudo make install
Checking your TV / Amplifier / Audio Processor capabilities
With ALSA 1.0.25 or later, Linux kernel 3.3 or later
Provided your hdmi device (TV or amp) was powered on before your PC started, Myth can display the audio capabilities of the device.
Go into Setup -> Audio. Select one of the ALSA:hdmi audio output device. In the description section, it will show the name of the connected device as well as the list of all the digital codec supported being one of the following:
DSD (One Bit Audio aka SACD)
As of Myth 0.25, only LPCM, AC3, DTS, DTS-HD and TrueHD are supported, with the caveats mentioned in the earlier section.