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Full Version: Problem downmixing Dolby TrueHD 7.1 to LPCM 5.1?
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I'm running an Intel NUC with Intel HD4000 graphics in Windows 7 hooked up via HDMI to a Marantz SR9600 receiver. Of note, the receiver can accept only Dolby Digital, DTS, and up to 5.1 LPCM over HDMI.

I'm trying to play back a Blu-ray with a Dolby TrueHD 7.1 soundtrack, and I'm getting no audio and a slow, stuttery picture, which I know indicates a problem with audio out. Since I know XBMC can decode TrueHD, my goal is to get near-lossless 5.1 LPCM output, but this doesn't seem to be working.

What audio settings do allow for proper playback:
5.1 channels + Dolby & DTS support + WASAPI or DirectSound output results in 5.1 Dolby Digital sound.
7.1 channels + Dolby, DTS & LPCM support + WASAPI or DirectSound output results in 7.1 LPCM sound - however my amp cannot properly accept this and gets confused, so all I get is left/right channels played back (however picture is smooth and what audio I get sounds fine).

What does not work:
Selecting 5.1 channels + LPCM support + WASAPI output gives me a stereo PCM signal, no audio, stuttery picture.
Selecting 5.1 channels + LPCM support + DirectSound output gives me a 5.1 LPCM signal, but no audio, stuttery picture.

No change when selecting "boost on downmix".

So, long story short, it seems there's a problem taking a Dolby TrueHD 7.1 signal and downmixing it to 5.1 LPCM. If it reencodes it to Dolby Digital 5.1, no problem. If it does a straight decode to 7.1 LPCM, it seems there's also no problem.

Any suggestions?
Please posts two screenshots of the two XBMC audio configurations screen you are trying

Additionally visit AudioEngine/HOW-TO:_Configure_audio#Audio_Output_Settings_Guide (wiki) and use that guide.

These are my main settings.


1) Shown like this, playing a 7.1 TrueHD audio track gives me no sound and stuttery picture. I have no problems with bitstreamed Dolby Digital or DTS soundtracks, or PCM decoded stereo tracks (ie. AAC, MP3, etc.)

2) If I change 5.1 to 7.1, I get smooth video and what I can only assume is 7.1 LPCM output, but my amp can't propery accept that audio format.

3) If I untick LPCM I get smooth video and 5.1 Dolby Digital output.

4) Changing from WASAPI to DirectSound slightly changes what formats my receiver claims it getting when there's no decoded sound (2.0 PCM vs 5.1 LPCM), but doesn't change any functional behavior.

5) For reference, 5.1 LPCM does work fine - for example if I select "output stereo to all speakers" or if untick Dolby Digital and DTS, I get proper 5.1 LPCM sound.

EDIT: further testing. If I select 2.0 channels, the video actually plays back properly. But if I select 2.1, 4.0, 7.0, essentially anything that isn't 2.0 or 7.1, it does not work. But as mentioned, if I use the same settings as in my screenshot but disable Dolby Digital and DTS capabilities and then go play a video using one of those codecs, I get 5.1 LPCM exactly as I would expect.
I wouldn't know for sure, as not use Windows+XBMC but you may want to look at Windows_Settings_for_AudioEngine (wiki) and make sure your OS parts are also correct. XBMC wise seems fine.

Yes, I did go through that when I built the system, before I selected WASAPI mode (which does improve bitstreamed performance).

I'm kind of wondering if this is an actual bug relating to what I'll admit is a non-standard situation (must be 7.1 TrueHD, must be LPCM output, must be output as something other than 7.1 or 2.0).
idk, you will have to wait for someone else to chime in, hopefully someone who knows their stuff audio wise.