Audio Passthrough issue on Intel NUC Coffee Lake.

iamforksu · April 13, 2019 at 2:50 AM

Hello.

I recently built a new LibreElec box and am having Audio passthrough problems on certain audio formats. DTSHD-MA and Dolby TrueHD are working, while Dolby Digital (AC3) and regular DTS are not functioning properly(no sound). Using the same files/receiver/cabling all audio formats passthrough fine on my previous LibreElec build(different computer and 8.2.x build).

Details of current setup:

- NUC8i5BEH1: Intel Core i5-8259U processor (2.3 GHz - 3.8 GHz, Quad Core, 6MB Cache, 28W TDP)

- Intel Iris Plus Graphics 655

- HDMI out from NUC to receiver (Pioneer VSX-1120) - capable of decoded all of these audio formats and still does on old Kodi machine

- LibreELEC release: Generic.x86_64-9.0.1

When I attempt to play a file encoded with DTS or Dolby Digital while on passthrough mode, I get no audio at all. My receiver seems to be getting an improper signal from Kodi while these files are playing, as it displays 'Dolby Pro-Logic' during playback. If I play back a DTS-HD or TrueHD file via passthrough, everything works perfectly. If I disable passthrough for specific format in question, Kodi will output PCM audio to receiver as expected.

- I have reset audio settings to default, rebooted. Same issue.

- I have changed audio passthrough device and changed back, rebooted. Same issue.

- Turned off specific passthrough formats and back on. Same issue.

- Log of issue: https://paste.ubuntu.com/p/4qshxh853v/

I play 3 files during debug capture:

1. Sopranos episode (Dolby Digital) - audio did not work

2. 21 Jump Street (DTS-HDMA) - audio did work

3. Movie '300' (DTS) - audio did not work

On a related note...... While playback is stopped, GUI sounds only function if 'Stereo Upmix' is turned on. When this is the case, my receiver is getting PCM sent to it. If I turn 'Stereo Upmix' off, my receiver again shows 'Dolby Pro-Logic'...... and no GUI sounds function.

Please let me know what other information I can provide to narrow down this issue.

jbinkley60 · April 13, 2019 at 10:15 AM

This is very interesting because I have a NUC8i7BEH and my results are exactly opposite. Dolby Digital and DTS work fine in passthrough mode whereas DTS-HDMA and TrueHD have no audio in passthrough mode. I am connecting to a Yahama RX-A3020 receiver. Using my older NUCs, a NUC 5I7RYH and NUC 6i5SYH both worked fine with 8.2.5 with passthrough on all formats. From what I have been following here in the forum I was under the impression that new Linux drivers are needed for the Coffee Lake NUCs to support bitstream audio such as DTS-MA and TrueHD. This is why I found your results so interesting.

**sky42** · April 14, 2019 at 10:59 PM

I do have trouble too with a i3-8100 on a ASRock b360 board with a Denon X4500H.

My workaround for now is use DP 1.2 + lspcon to HDMI 2.0 for Video direct to the tv and for audio the 2nd Video Port HDMI 1.4 to the AVR just for the audio. Then all formats are working as expected.

I did not do a full matrix test with all combinations of software / hardware config, because I have a workaround.

jbinkley60 · April 15, 2019 at 7:19 PM

I tried your approach but had issues with the menus disappearing in this thread . I ended up using an HDMI splitter but bitstream won't work right now if I change to HDMI 2.0 resolutions (i.e. 3840x2160 @60fps.). if I change to HDMI 1.4 resolutions (i.e. 3840x2160 @30fps.) bitstream audio works fine. This is definitrly an Intel driver or similar type of issue. One thing different I see with your configuration and my testing is I ran video out the HDMI port and audio out the DLP port. You reversed this. I may give it a shot and see what happens. The HDMI splitter gives me the advantage of plugging in any HDMI device and splitting off the audio to my HDMI 1.4a receiver. Right now I am running a Vero 4K+ and it works perfectly with 3840x2160 @60fps and bitstream audio.

jbinkley60 · April 17, 2019 at 5:55 PM

I tried the reverse configuration with the video going out the display port and the audio going out the HDMI port. Got the same lost menu issue and bitstream audio didn't work. I'll wait for the updated drivers. Right now I am using a Vero 4K+ and it works fine. I eventually want to move back to the NUC with LibreElec but want full HDMI 2.0 support with bitstream audio to both work.