On Board HDMI Audio Noise Issues

Discussion in 'Home Theater PCs & Equipment' started by Zarathustra[H], Jan 4, 2020.

  1. Zarathustra[H]

    Zarathustra[H] Official Forum Curmudgeon

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    Hey all,

    I have a HTPC setup in my livingroom where a HTPC running Kodi (on top of LibreElec) passing both video and audio via HDMI to my surround receiver, usually via either passthruough, or multichannel PCM.

    For the longest time the system was running on an old dual core Haswell system, utilizing an Nvidia GPU for video output. When this was the case my system was working fine.

    However, the douchebags over at Nvidia decided that they were going to discontinue VDPAU (their video decode hardware acceleration API under Linux) and it's replacement NVDEC has pissed off all of the open source projects, so they are refusing to use it. (AMD and Intel use VAAPI, but Nvidia sees a need to be proprietary and different as they always do...)

    So, due to VDPAU having been discontinued and stagnating, it is not getting the latest features and formats anymore, at the same time all the Kodi and LibreElec devs are saying that on x86 they are primarily developing on and for Intel integrated graphics these days, so I decided to switch things up.

    A couple of months ago I picked up an Asrock B365M Pro4 motherboard, and because all the low end CPU's for the platform were sold out for some reason, I wound up with the total overkill for simple video playback duty, Intel i5-9400

    It's a great little platform, but it introduced a new problem. Audio using HDMI straight off the motherboard has noise problems at low volumes which were never there before. I usually cant hear it over loud scenes, but when nothing is playing it is super obvious, and sometimes audible during very quiet scenes.

    It's bugging the hell out of me.

    Since HDMI is a digital format, it shouldn't have any analog noise going out over it, which is why I am suspecting some sort of odd ground loop. I've been looking for HDMI ground loop isolators without success.

    Does anyone have any suggestions?
     
  2. pendragon1

    pendragon1 [H]ardForum Junkie

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    only time ive had this happen was with a really cheap cable. have you tried another cable yet?
     
  3. Zarathustra[H]

    Zarathustra[H] Official Forum Curmudgeon

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    Hmm. I'm not sure that is it, as I had no noise while using the GPU, and do have noise when not using it, with everything else remaining the same, but do you have any recommendations for what you consider "good" HDMI cables?
     
  4. N4CR

    N4CR [H]ardness Supreme

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    Use a cheater plug or a travel adaptor without ground on the amp end or on your TV. That solved all my noise issues (TV was causing some nasty ground interference into the amp power feed board, even though TV has nothing to do with the sound loop - it's using 1080/60 VGA from HDMI adaptor lol!). I think you burgers have no ground normally though? Not sure, your electrical system is uhh... a little ancient :).

    Good luck!
     
  5. pendragon1

    pendragon1 [H]ardForum Junkie

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    not really no. if you have another cable kickin around try it instead just to rule it out.
     
  6. Zarathustra[H]

    Zarathustra[H] Official Forum Curmudgeon

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    That's a common misconception, but I usually only hear it from Brits.

    The National Electric Code in the U.S. has required three prong grounded outlets be installed in all new home construction since 1962.
    For homes built prior to 1962 - however - chances are there are a lot of ungrounded two prong sockets still in place. In many larger cities that can be a significant proportion of the housing stock.

    My current house in a suburb of Boston was built in 1927. My previous house in the same suburb was built some time in the 1830's (records were poor at the time). The 1830's home had its electrical system upgraded to current standards at some point. In my current home it has been upgraded in MOST rooms. In fact, I think all rooms except for the Dining room for some reason.

    Either way, it just goes to show that there are a lot of legacy outlets still around.


    Just like how your Type I plugs in kiwiland can have two or three prongs depending on whether or not they are grounded, so can ours, we just give them different type names. The two prong is a type A (or NEMA 1-15), the three prong is a Type B (or NEMA 5-15). We also have less common plugs for 20amp circuits. This is much how most of Europe uses the Type C connector for two prong ungrounded, and the Type F connector for grounded connections.

    1280px-NEMA-AC-Power-Plugs.jpg

    Ungrounded two prong NEMA 1-15 on left, grounded three prong NEMA 5-15 on right.


    Our electric grid uses different specifications that those in many parts of the world, but our 60hz 125v standard is just a different way of solving the problem compared to 50hz 230V, and by no means antiquated.

    It would probably be more efficient to use higher voltage and lower current, but it is mostly irrelevant due to the short, in-home distances involved. The last few mile distribution is carried at 7.2KV, and stepped down in a distribution transformer on your street to 125v/250v before entering the home. Normal residential power is as above 125v 60hz, but most houses also have a few 250v circuits for stoves, clothes dryers and other major appliances.
     
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  7. Zarathustra[H]

    Zarathustra[H] Official Forum Curmudgeon

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    All of that said, can you provide more information other than "cheater plug"? Do you mean one of those units that bypasses the ground and turns it two prong?

    I would have thought ground loops would be unlikely to be the cause, as the HTPC, the Receiver (and the amp) are all plugged into the same circuit.

    I was thinking maybe some leakage current or ghz noise from the PC is somehow being carried over the grounded shielding in the HDMI connector...
     
  8. N4CR

    N4CR [H]ardness Supreme

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    Firstly, thanks for the education on US electrical standard, glad to hear it has been changing quite a bit in the last decades. I have not traveled there but instead been to US territories and the electrical situation was not unlike other third world countries... not fun getting shocks from un-grounded equipment when working outside.
    I also heard that it's common to only have 10A feeds in USA, which led to much griping from larger, custom sub array loving HiFi geeks like ourselves. But nothing a 20A feed can't solve if your wiring is up to it.


    Indeed.
    I also didn't think a ground loop was the issue initially but you could be right - it may indeed be some GHz type leakage as it's pretty high frequency.

    Basically it came over the HDMI > VGA converter and was only present when the TV was plugged in and connected to the PC (even on UPS etc). There is nothing to do with audio chain directly, as it's a video-only connection in my case, but it did cause what I am now pretty sure is ground interference somehow. Audio is handled via AUX in my setup (2.1) so it does not travel over HDMI, it goes direct to the amps via a very long 3.5mm jack.
    Removing the ground from TV (also plugged into amp distro/circuit as your setup is) fixed my problems, so i'd hazard a guess we have similar issues. At least cheap and quick to test, so in your case maybe the receiver or first port of call for HDMI signal chain from PC would be the first place to try this, at your own risk of course.

    Good luck!