Question Coax causing audio issues

Jul 20, 2020
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I recently switched to a monitor (no speakers) from a TV that I use for both PC and cable tv. Since I'm using a monitor now, I use the headphone out port on the monitor to the line in on my PC. The cable box is connected to the monitor via HDMI. I get audio but my problem is that I also get a ground loop buzzing sound at like 60hz and since I use a subwoofer this is really annoying. I noticed the only thing that makes the buzzing sound go away is disconnecting the coax cable from the cable box (which then I can't watch TV). This buzzing noise still occurs even when the cable box power cable has been disconnected. If the coax cable is connected to the cable box I get that humming, as soon as its disconnected the noise goes away. I'm not sure what to do at this point. Is it possible there is a bad coax splitter or cable that could be causing this issue? Does anyone know any workarounds to this issue? Thanks!
 

Sonic Illusions

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Feb 16, 2019
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If you're getting a good picture, I doubt the issue's cause by a bad splitter. How was the TV's audio connected to the cable box? Was it HDMI? If not, check the audio output settings on your cable box to be sure it sends the audio to the HDMI output. Other than that, it sounds like you have everything connected properly, so one thing I can think of is to check the grounding of the coax where it enters the building. There should be a nice, tight, solid earth ground going from the junction to a rod sunk into the ground or otherwise connected to a solid earth ground. Also, what are your components' AC power cords connected to? Do you have good quality line-conditioning/ isolating power distribution...a UPS connected to your PC? Even the UPS outlets not connected to the battery backup will have AC line conditioning/ stabilization. Plug your cable box in there. You can't have any surround at all, from an analog audio signal with a stereo headphone jack, but you most likely already know that. Does your cable box have a TOSLINK optical out and your PC an input (SPDIF) for the same, to experiment? The HDMI and TOSLINK are both digital audio, BUT the headphone jack is analog only. Usually, you only have hum with analog connections, so I think you're on the right track to suspect the coax/ cable box. You can even try the analog audio outs (no surround signal) from the cable box, to the PC, but you may need to go to the box's audio setup and choose the audio out. Clean the headphone jack by spraying electrical contact cleaner into the jack, then quickly plug and unplug the plug into the jack several times. Hum can also come from a dirty/ unused jack and since this is a different monitor (new? used?), don't ignore the jack. Start with the jack and the audio out setting on your cable box. Hopefully, one of these ideas will work. Good luck! If none of this works, post your monitor, cable box and PC/ sound card model #'s.
 
Jul 20, 2020
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Thanks for the reply! The picture quality never has any issues which makes me think that its a grounding issue. Previously the cable box was connected via hdmi cable to the tv and the tv speakers were used. I replaced the splitter on the outside of my house with a new one from verizon and grounded it to the grounding rod outside since the old one wasnt grounded but it hasnt fixed the issue. I think its odd that even when the cable box isnt getting any power, the humming/buzz noise still travels through the hdmi to the monitor and then from the monitor to pc via headphones out to line in. I dont have any sort of UPS, but have considered purchasing a cheap one. Im not concerned about surround sound at all, i would be happy even with mono audio as long as there is no hum. TOSLINK is a possible solution but I would have to purchase a sound card with optical in. When I have the cable box connected to the monitor via hdmi and monitor to pc via headphones out/line in, i get no buzz when the coax is disconnected. Everything except the cable box is new, heres what I have:

IP1100 cable box
LG 32GK850G monitor
MSI Z490 gaming edge wifi motherboard with basic realtek audio ports
MAudio Mtrack hub connected via USB to PC

Edit: I tried a RCA cable from the audio out RCAs on the cable box directly into one of my KRK rokit 8s RCA input and still got loud hum/buzz
 
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Jul 20, 2020
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I purchased a coaxial ground loop isolator that should hopefully get here on Thursday\Friday. I will update if this helps at all. My guess is since both the AC and coax are grounded outside the house but are connected through the cable box (with no ground pin) and HDMI to monitor (with ground pin) it is creating a giant antenna. So basically coax is grounded outside the house, comes in and is split a few times, connects to the cable box, which then is grounded through the HDMI cable to the monitor and through the monitors power cable back out to ground? Does that sound right? I deal with digital lines quite often (fiber, cat5, cat6), but never analog lines like coax where these issues can occur. I can live with a ground loop isolator connected, thats not a big deal, just want to make sure there is nothing wrong with the wiring in this house. Any input is appreciated! Thanks

Update: FYI, just touching the shielding on the coax cable to the threads on the coax port on the cable box (aka center pin in coax not connected) I get noise. Perhaps there is a crimped coax cable in the attic or something? A coax cable somewhere where the center pin is touching the shielding because of a crimp?
 
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Sonic Illusions

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Feb 16, 2019
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The interesting thing is the signal coming through the copper COAX line is digital, but still needs to be shielded/ grounded. I actually doubt the hum is from the COAX connection/ bad sheilding/ ground. If it was, then most likely, you would see video artifacts as well. What was the only thing you changed? The monitor. That's when your trouble started. There was previously an internal amplifier, which powered your speakers. Now, you're using your PC connected through the monitor's HDMI port and then to the analog earphone out. That may be where the problem is. Are you still using the same HDMI cable? This is on P. 25 of the monitor manual: • "Depending on the audio settings of the PC and external device, headphones and speaker functions may be limited" You may want to try connecting the cable box's analog RCA outputs to the LINE-IN on your PC. Getting the audio signal directly from the source may solve the problem....theoretically!
 
Jul 20, 2020
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Thanks for the reply! The odd thing is that going from the rca out on the cable box directly to one of my speakers does not resolve the issue. I think that should eliminate the pc and monitor as part of the issue. The speaker uses a 3 prong power plug and should be grounded. The thing that confuses me the most is that when the shielding or screw on connector on the coax cable is touching the threading or even the metal casing around one of the rca ports on the cable box, the input line on my pc shows a constant input signal. I should be able to test with the coax ground loop isolator soon to see if it makes any difference. I also ran the rca out on the cable box to an old USB audio interface that had rca inputs, still got hum.
 
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