Motherboard HDMI Audio Noise Issues?
#1
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?
Livingroom: 65" Panasonic Plasma, Denon AVR-x3300w, Parasound A31, Fronts: RBH SX-6300 Towers, Center: RBH 441-se, Surrounds: RBH 41-se Sub: Dual SVS PC13-Ultra, Source: Custom Kodi Box
Desk: DAC: Schiit Modi Multibit,Headphones: Schiit Jotunheim -> Sennheiser HD650 & Beyerdynamic DT770 Pro, Speakers: Parasound 275v2-> RBH 41-se & SVS SB12-NSD
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#2
(2020-01-05, 00:16)mattlach Wrote: HDMI is a digital format
Yes unless there is new digital data introiduced within the source (you are using wasapi & pass-through?), you should be hearing dead air, save for some low level amplifier hiss generated at the digital to analog interface. In settings>system>audio [expert mode] check you haven't got the 'send low volume noise' toggled. In days gone by this issue was just tying up the ground of the separate devices (just a copper wire between the amp/pc/display). What sound frequency are you hearing, and is this sound appreciable at the start of a video when there is zero sound?
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#3
Do you have any noise emitting equipment in the vicinity? Maybe read some articles on HDMI noise suppression, like this one...
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#4
I did not see this one mentioned..
Kodi Settings... system settings... audio...
1. Keep audio device alive...
2. Send low volume noise...
There are two options that may help.. or perhaps one is on when it should be off?
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#5
(2020-01-05, 00:16)mattlach Wrote: 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?


Can you describe the noise?  Is it a low frequency hum or more white-noise static?

Does it disappear if you passthrough Dolby Digital, DTS, DTS HD MA/HRA, Dolby True HD - or is it there on both passthrough and PCM stereo / multichannel (where you've decoded DD, DTS, AAC, FLAC, MP3, MP2 etc. to PCM for HDMI output)?
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Motherboard HDMI Audio Noise Issues?0