Laptop to TV buzzing sound that changes with picture - AVS Forum
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post #1 of 21 Old 03-07-2012, 11:31 PM - Thread Starter
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I have my laptop's headphone jack connected to my LG LCD TV's audio in via a simple 3.5" cable, and there's a buzzing sound coming out of the TV's speakers that seems to change with what's being displayed on the TV. It *seems* related to the brightness, but sometimes a display with many colors will be louder than a display that's predominantly white.

I've tried plugging the TV and the laptop's power into the same power strip, and even unplugging the laptop's power adapter completely, and even changing the TV's brightness/constrast, but they don't make any difference. I've also made sure to mute the microphone volume in Windows (even though there's no mic connected). The headphone port is the only means of getting audio out from the laptop, and external speakers are not an option in my situation.

What can I do to solve this?
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post #2 of 21 Old 03-08-2012, 05:28 AM
 
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Wrong impedance, along with a bad cable, is why you are getting the buzzing.
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post #3 of 21 Old 03-08-2012, 05:50 AM
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It has nothing to do with impedance.
Possibley due to poor power supply filtering in the display.
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post #4 of 21 Old 03-08-2012, 08:12 PM - Thread Starter
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So is the best solution to try a new cable? If so, which one's a better bet? Another 3.5mm to 3.5mm cable or a 3.5mm to RCA one? If someone has a link to a cable they bought and is problem-free that would be great!
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post #5 of 21 Old 03-09-2012, 05:19 AM
 
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There is no magical cable. It is more trial and error. You could order one from monoprice.com that is a heavier wire gauge and shielding, but it may not solve the problem, due to most likely it is a impedance issue.
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post #6 of 21 Old 03-09-2012, 05:40 AM
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Please explain how this is due to an "impedance issue"?
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post #7 of 21 Old 03-09-2012, 06:10 AM
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Quote:
Originally Posted by suan View Post

I have my laptop's headphone jack connected to my LG LCD TV's audio in via a simple 3.5" cable, and there's a buzzing sound coming out of the TV's speakers that seems to change with what's being displayed on the TV. It *seems* related to the brightness, but sometimes a display with many colors will be louder than a display that's predominantly white.

I've tried plugging the TV and the laptop's power into the same power strip, and even unplugging the laptop's power adapter completely, and even changing the TV's brightness/constrast, but they don't make any difference. I've also made sure to mute the microphone volume in Windows (even though there's no mic connected). The headphone port is the only means of getting audio out from the laptop, and external speakers are not an option in my situation.

What can I do to solve this?

If the sound coming out of the laptop's headphone jack is clean when you listen with good headphones, your next good move would be to pick up a $20 Ground Isolator from Radio Shack.
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post #8 of 21 Old 03-09-2012, 10:14 AM - Thread Starter
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Originally Posted by arnyk View Post

If the sound coming out of the laptop's headphone jack is clean when you listen with good headphones, your next good move would be to pick up a $20 Ground Isolator from Radio Shack.

Even though the issue still exists when the laptop is just running on battery power and not connected to the power from the wall at all?
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post #9 of 21 Old 03-09-2012, 10:18 AM
 
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Quote:
Originally Posted by suan View Post

Even though the issue still exists when the laptop is just running on battery power and not connected to the power from the wall at all?

Do this. Get a pair of powered speakers for a computer desktop and connect the laptop to them, to see if you still get the buzzing. If you don't, then it is a impedance issue between the laptop and tv.
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post #10 of 21 Old 03-09-2012, 10:26 AM
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...except that a mismatch in impedance will not cause hum or buzz.

If you still get buzz on a headset, while running on battery power with no other connections, then the laptop is at fault.
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post #11 of 21 Old 03-09-2012, 10:35 PM - Thread Starter
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Perhaps I should add some more detail.

I've lost track of exactly which ones I ordered, but the current 3.5mm cable I'm using is similar to this: http://www.amazon.com/3-5mm-Stereo-M...1361209&sr=8-5 (no gold plating or explicit shielding)

There is also a VGA connection between the laptop and the TV, and the TV also has a coaxial cable connection to the wall. I'm pretty sure the buzzing only happens when the TV's set to PC/RGB mode and the laptop is driving the display (staying at a channel which is just a black screen when in cable mode produces no buzz, but I'm not sure if this is an adequate test)

Also, there's a wireless router less than 2 feet away from the laptop (both the laptop and router are below the TV) Perhaps this is a source of the buzz too?

Unfortunately I'm away for the weekend so I'll have to wait till Sunday night to troubleshoot further.
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post #12 of 21 Old 03-09-2012, 10:42 PM
 
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Okay. If it only happens when you connect the RGA cable, that means that your laptop is not allowing a complete ground connection back to the tv, even if it is on battery power. If it happens with just the sound cable, it is a impedance issue.

Either way, it is still a issue of impedance, otherwise you would not be getting the problem. Cut and dry.
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post #13 of 21 Old 03-10-2012, 04:04 AM
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Quote:
Originally Posted by gregzoll View Post

Okay. If it only happens when you connect the RGA cable, that means that your laptop is not allowing a complete ground connection back to the tv, even if it is on battery power. If it happens with just the sound cable, it is a impedance issue.

Either way, it is still a issue of impedance, otherwise you would not be getting the problem. Cut and dry.

These are all unbalanced connections. If there were no ground connection there'd be no signal.

This has absolutely nothing to do with impedance. Insisting that it does, while refusing to provide any explanation of how or why, is making me think that you're not 'quite right'.

The only thing 'cut and dry' here is that you don't know what the word "impedance" means.
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post #14 of 21 Old 03-12-2012, 08:39 AM
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Quote:
Originally Posted by SAM64 View Post


These are all unbalanced connections. If there were no ground connection there'd be no signal.

This has absolutely nothing to do with impedance. Insisting that it does, while refusing to provide any explanation of how or why, is making me think that you're not 'quite right'.

The only thing 'cut and dry' here is that you don't know what the word "impedance" means.

Please search for common impedance coupling. Jensen Transformers have written a few useful papers on it. And no need for insults!

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post #15 of 21 Old 03-12-2012, 09:24 AM
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Why don't you explain how an impedance mismatch will cause hum? Gregzoll can't, maybe you can?
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post #16 of 21 Old 03-22-2012, 09:37 PM
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Hello. Bit of a long story but please help me. I have recently finished my basement and used a (very thin and cheap) RCA cable to connect a tv in a seperate room of my house from a dual tuner PVR satellite receiver. problem is now that basement is done I am unable to replace my poor quality cable. Now my tv connected to the RCA gives off a very loud buzz noise from my speakers. When I unplug the L/R audio and leave the video connected the buzz stops. When I plug back in... I almost go crazy from this buzz! I have been researching and I think this my help. I also read about "RCA attenuator" to reduce signal due to "over modulation" This is getting complicated to me. please help. Thank you

Darryl
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post #17 of 21 Old 03-22-2012, 09:43 PM
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Can you explain in more detail what the connection is? Do you have one video cable and a pair for audio?

What happens if you just leave the center pin on the RCA audio connected and no push them enough in for the outside ground to connect?

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post #18 of 21 Old 03-23-2012, 05:10 AM
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yes ok.... it is the composite yellow video and white and red left right audio. When I dont push the connection in all the way the buzzing is actually louder. Some channels are worse than others. I notice movies and normal shows are not so bad, but sports channels like TSN sports center or NHL network it is TERRIBLE!! like when graphics are on... ticker line showing scores... graphics with the colour red are very distinct! like I said before i know my cable is cheap my mistake. I have just never run into this problem before. So in my research I came across RCA attenuator which was described to me to fix the problem suspected to be "over modulation" whatever that is. said something about over modulation of video interfering and bleeding over into my audio lines causing the buzz or humm. I have seen them available to filter or reduce the signal strength from .5db to 6db?? you heard of this? then the "RCA ground loop noise reducer" this is supposed to reduce noise with grounding.... I dunno. I do know it is mainly ment for car audio. But as I watch sportscenter.... depending on colours displayed (mainly reds and white affect most) and graphics the level of the buzz changes. It really seems like some kind of interference in the audio. Does this explain it better?
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post #19 of 21 Old 03-23-2012, 05:40 AM
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Quote:
Originally Posted by SAM64 View Post

Why don't you explain how an impedance mismatch will cause hum? Gregzoll can't, maybe you can?

As a general rule, hums aren't often fixed by precisely matching impedances. Audio as we know today it is not based on impedance matching. In fact it is based on consciously mismatched impedances, those where the source impedance is only a tiny fraction (hopefully less than 1%) of the load impedance.

What Jensen transformers often do for audio is break undesired conductive paths. They address ground loops and ground potential differences. Thing is, if money matters you can get an audibly equal bang for a lot less money with a Radio Shack Ground Isolator or its equivalent.
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post #20 of 21 Old 03-23-2012, 05:48 AM
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As a general rule, hums aren't often fixed by precisely matching impedances.

Yes, I know.

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Audio as we know today it is not based on impedance matching.

Yes, in fact pro audio did away with this decades ago.

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In fact it is based on consciously mismatched impedances, those where the source impedance is only a tiny fraction (hopefully less than 1%) of the load impedance.

Yes, often referred to as "bridging the load".
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post #21 of 21 Old 04-04-2012, 07:50 PM
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I spent $12 on ebay and bought a ground loop isolator and bam!!!! BUZZZZZZZ gone!!!!!!!!! clear as a bell! Thanks!!!!
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