Audio hum w/external display?

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Audio hum w/external display?

Hi all.
I'm outputting the video from my MacBook Air (2nd gen) to a plasma using a minidisplay port to DVI and HDMI adapter. The picture is stellar but the sound has this annoying high-pitched humming whenever the video is going. As soon as I turn off the external video, the hum disappears. All other audio when not running external video is fine too.

So I'm wondering -- will a shielded audio cable help? Or is this just a problem with the MacBook Air and external video? Or is it the result of the recessed audio port? Or do I have a lemon?

Anyone else experience this?

Thanks for any feedback.

MacBook Air 1.86, Mac OS X (10.5.6), eMac, iPhone

Posted on Feb 12, 2009 12:54 PM

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Answer 1

afbradley Author

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Feb 13, 2009 9:50 AM in response to afbradley

Okay, I think I found my own answer and I'll post it for anyone else who has this problem in the future.

Apparently, I need a Ground Loop Isolator. It eliminates hum created when audio and video sources are combined and someone about both systems aren't properly grounded or something.

In any case, it's about $25 bucks at Radio Shack or The Source and simply goes between the audio output from the computer before it gets to the amp.

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Answer 2

Feb 27, 2009 1:22 PM in response to afbradley

You're exactly right. I just went through the same process that you did, and ended up at the same conclusion. The external audio hum is apparently a known issue when connecting a Macbook, Macbook Pro, or Macbook Air to an external TV monitor using the DVI port...

(See the "audio noise when using DVI out" post)
http://discussions.apple.com/thread.jspa?messageID=6377740&tstart=0

_*If you've isolated the issue to a hum when you connect your DVI port, the only viable and successful workaround is to buy a ground loop isolator for your audio cabling.*_

Instead of begrudgingly paying RadioShack $25, I picked mine up on ebay for about $7, including shipping.

http://shop.ebay.com/?from=R40&_trksid=m38.l1313&_nkw=groundloopisolator&sacat=See-All-Categories

Thanks for sharing your similar experience!

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