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Buzz/Hum in audio lines from computer connected to HDMI television

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Justin Toney
Buzz/Hum in audio lines from computer connected to HDMI television
on Oct 15, 2017 at 9:26:26 pm

In this setup I have a laptop sending video to some televisions with no audio through that. The audio comes out of the 1/8" connection on the laptop and is sent directly to the sound console. When the HDMI cable is connected, I get a buzz in the audio which disappears immediately after I remove HDMI.

The HDMI cable is an extender over CAT5. The televisions are about 75 feet away from me. My question is what do you think I could do to clean this audio?



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Richard Crowley
Re: Buzz/Hum in audio lines from computer connected to HDMI television
on Oct 16, 2017 at 12:55:56 pm

Does this happen when the laptop computer is operating from the internal battery (with the power DISconnected)? Does the audio hum when you listen on the computer internal speakers? Does this happen when you have a LOCAL monitor connected via HDMI?

This has all the symptoms of the chronic problem with many laptop computers. There is a terrible ground-loop problem and is frequently solved by simply using isolation transformers. It could be something as simple as:

https://www.radioshack.com/collections/a-v-couplers-adapters/products/radio...

or a pair of these:

http://www.rolls.com/product.php?pid=db25

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Justin Toney
Re: Buzz/Hum in audio lines from computer connected to HDMI television
on Oct 16, 2017 at 8:02:01 pm

Normally a ground lift works but this machine doesn't have a ground.



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Richard Crowley
Re: Buzz/Hum in audio lines from computer connected to HDMI television
on Oct 16, 2017 at 8:08:56 pm

But many (most?) laptops have incredibly noisy "line lump" power supplies. Regardless of whether the power mains cord has a ground or not. Since laptops have internal batteries, it is trivial to do the experiment where you completely remove the power cord to see if that causes (or contributes to) the noise problem. The problem is actually larger than simply "ground loop" and I should have stated my previous response better. And then you have the added issue of the ground-reference from the HDMI extender gadgets.

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Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.


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Justin Toney
Re: Buzz/Hum in audio lines from computer connected to HDMI television
on Oct 17, 2017 at 6:01:43 am

Removing power did not make the situation better or worse, like I had imagined.



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Justin Toney
Re: Buzz/Hum in audio lines from computer connected to HDMI television
on Oct 22, 2017 at 4:17:39 am

Any other ideas on how to fix this issue?



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