Windows Vista to Output to Dolby Digital?



I am currently running Vista, SP1. Sound chip is a RealTek HD output
through SPDIF (coax), run to my AV receiver.

How do I get windows to output all audio (including windowd default
sounds) to Dolby Digital? Right now it outputs everything to 2.0
PCM. I have enabled digital output (spdif), and DD and DTS in the
control panel. I have done the test, and heard the tone on all
channels (and when it does the tones, Dolby Digital kicks in of
course, but then goes back to PCM after the test).

I know digital out is working because like I said, it does the test in
DD, and also, I have installed AC3 Filter, and when I play movies, the
audio switches to Dolby.

Any ideas?


If the source sound isn't encoded in multi-channel Dolby format I wouldn't
expect Windows to output it as Dolby. In the AC3 filter documentation about
SPDIF it states "Sound card downmixes multi-channel sound into two channels
before sending it over SPDIF. Uncompressed sound transmitted over SPDIF is
always stereo!".

Emulated multiple channel sound output is a separate issue, as is sound
encoded in AC3 and the actual AC3 filter configuration. I can't use the
digital output on mine (yet. - Realtec 880 so it might have different
options than yours) but looking at the available settings there is no output
option for anything other than 2 channel sound in the Windows "sound"
control panel applet for the digital output. Neither is there a multiple
channel or speaker setting in the Realtek applet for the digital output.
That suggests any multi-channel or surround sound emulation has to be
provided by the digital receiver or speaker amplifier itself. The
documentation from AC3 states " Some sound cards can encode the
multi-channel sound before sending it over SPDIF. But this option is rare .
.. ." There is a check box for Virtual Surround in the Windows Sound
settings (digital output), under Enhancements, but I can't tell whether it
would be useful from the description. It might work for multi-channel sound
tracks but not add emulation for stereo sound tracks.

The AC3 filter has its own configuration settings. I don't imagine the
various speaker configurations that it has available will have any effect on
the SPDIF output but AC3 filter has a setting for Dolby Surround/Prologic on
the Main and Mixer tabs that might be relevant. You can try the different
options on the SPDIF tab as well but on the System tab if you enable AC3
filter for PCM, Windows will use the AC3 filter to process sounds that
weren't originally encoded in AC3. That should include outputting PCM over
SPDIF output as there is a "disable" option provided to block that function.

Would be interested to see if you find a solution.

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