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Audio Hum on SD not HD

post #1 of 35
Thread Starter 
I know there are lots of threads about audio hums. Many caused by "ground loops" I understand. But I have a situation that seems different or at least odd to me. I have a TivoHD connected by HDMI to an Onkyo 606 receiver. Before you ask, the receiver has been back for "the known hum issue" and even back for a second time as the hum was still present. The authorized service center couldn't repeat the hum. Anyway, here is what I think makes this situation odd to me. When I'm watching/listening to an HD channel (and 5.1 audio) there is no hum. But when I'm watching "regular SD TV" the hum is often present and sometimes very noticeable. It's mainly noticeable when I pause TV. It's even there on the Tivo menus. But again it will disappear when listening to 5.1 and I hit pause. What would make the hum come and go depending on that?

Thanks in advance for any ideas.
post #2 of 35
Does hum occur with the Tivo directly connected to the TV?
post #3 of 35
Thread Starter 
Well that's hard to do. All my components are in a closet on the other side of the room and my TV doesn't even have the speaker bar it came with on it any more. I just noticed I forgot to mention I have a 7.1 setup. I plan on doing more testing for example with the DVD and CD players to see if it happens there. But what seems very odd is that I can make it come and go (most of the time) by basically changing channels (between SD and HD). As for ground loop possibilities. All components except the TV and subwoofer are plugged into the same outlet. The TV is in another (remember no speaker just picture which is fine) and the subwoofer is plugged into yet another. Perhaps my first test should be to replace the HDMI cable running from Tivo to receiver with component cables and see if it happens then too. What do you think?

edit: I know having speaker wire near electrical power cables can produce a hum. Would that hum only happen in the speaker the speaker wire is running to or all speakers at the same time? Also what about the tangle of wires behind all the components (including their respective power cords).
post #4 of 35
Carry the Tivo with an HDMI cable from the closet to the TV. That takes one component out of the equation.

Test with other sources beforehand if that's easier.
post #5 of 35
Thread Starter 
I will probably check the other sources first as I don't have any speakers on the TV and taking the Tivo to it won't do much unless I dig out the original speaker bar and reinstall that. And I know that won't be easy to reconnect. Thanks.
post #6 of 35
Thread Starter 
Well a very quick test using the DVD player (not HD or Blu-Ray) and I get the hum there too. Not as loud but there. But again I switched back to TV on SD and the hum is still there. Switch to HD channel with my ear next to a speaker (by the way the hum is coming from all speakers) and I can hear it "switch the hum off" and it's not present on the HD channel even when I pause it, it's perfect.

Well a very quick test using the CD player and it's there too.

So my apologizes to Tivo. It's not just that. But still odd I can affect the hum by changing channels.

I guess my only option is to start unplugging components and see what is causing it. Could it be the HDMI hum I have heard about? And I wonder why is has just started (again).

Thanks.

Edit: While eating lunch I was watching a HD channel. No hum. Then all of a sudden the hum starts right in the middle of live TV. BUT it stopped when I hit pause! And this hum was louder than before. So I'm now at a complete loss as all my earlier statements are wrong and I'm back to square one. I now have a hum that comes and goes at will. Would a ground loop do that or is a hum caused by them present all the time?
post #7 of 35
It very well may be a ground loop of some sort and process of elimination may help identify the culprit.

Just a guess... but there may be something "flaky" in the A/V receiver with HDMI circuity and/or using Dolby Digital vs. "other" surround processing or PCM stereo.
post #8 of 35
Thread Starter 
I have just had a thought. I have a signal booster for the cable coax in the attic and of course it is plugged into a different power outlet. I haven't had a chance to take it out and see what happens, but can they cause ground loop issues in the audio?

Edit: of course it has been there for a while so I don't know why it would suddenly now start to cause problems.
post #9 of 35
Quote:
Originally Posted by britdiver View Post

Anyway, here is what I think makes this situation odd to me. When I'm watching/listening to an HD channel (and 5.1 audio) there is no hum. But when I'm watching "regular SD TV" the hum is often present and sometimes very noticeable. It's mainly noticeable when I pause TV. It's even there on the Tivo menus. But again it will disappear when listening to 5.1 and I hit pause. What would make the hum come and go depending on that?

AFAIK, only the TIVO knows whether it is in HD or SD mode, so it is the probable source of the hum.
post #10 of 35
He gets hum with CD and DVD players also.
And... only the receiver knows if the audio is DD2.0, 5.1, or PCM stereo and/or when to apply DPLIIx.
post #11 of 35
Thread Starter 
Some limited testing done and with news to report. I can make the hum come and go by disconnecting and connecting the coax going into Tivo. Now although I get the hum from the other sources (CD and DVD) remember Tivo is ALWAYS sending its signal to the receiver even if it's not being output. There is no "off" button on Tivo. I even managed to make the hum come and go over a recorded show. When the coax is hooked up, it hummed. When not connected, no hum over the recording. Now I believe the coax cable is grounded where it comes into the house as there is what looks like a ground cable connecting the coax "box" and the mains electrical box on the outside of the house which is a few feet away. So here my questions and thoughts:

1. Is it worth calling the cable company to check the grounding?
2. Could the signal booster in the attic being causing or at least adding to the problem? Although it has been there all this time and the hum is relatively recent.
3. Is there a "device" I can put inline with my coax to eliminate this hum? And by device I don't mean a $500 box.

Thanks.
post #12 of 35
Have you unplugged the signal booster to see if the hum goes away?
It's possible that the power supply caps. have dried out, resulting in hum on the line.
post #13 of 35
If you disconnect the coax from the Tivo and the "hum" disappears while viewing/listening to a recorded program, that should tell you that the "ground loop/hum" is being introduced before the Tivo and essentially eliminates the Tivo, Amp, speakers, CD/DVD player.

Suggestion:
1) bypass the amp in the attic to test (use a F-type barrel/coupler connector)
2) call your cable provider to check/fix grounding
post #14 of 35
Thread Starter 
Quote:
Originally Posted by duvetyne View Post

Have you unplugged the signal booster to see if the hum goes away?
It's possible that the power supply caps. have dried out, resulting in hum on the line.

"power supply caps have dried out"... I'm sorry I don't really know what that means.
post #15 of 35
Thread Starter 
Obviously I'm going to just try removing the booster first, and call my cable company before I buy anything, but has anyone used either of these devices to help with hum:

1. Jensen IsoMax VRD-1FF
2. Mondial Magic Splitter

Thanks.

P.S. Each about $60.
post #16 of 35
Quote:
Originally Posted by britdiver View Post

3. Is there a "device" I can put inline with my coax to eliminate this hum? And by device I don't mean a $500 box.

Very good chance of that:

http://www.123securityproducts.com/v...&CS_010=vid-gl
post #17 of 35
Quote:
Originally Posted by britdiver View Post

"power supply caps have dried out"... I'm sorry I don't really know what that means.

It means it's old and it's failing. the power supply caps are no longer effective filters and are allowing 60 or 120 hz hum on the output.
post #18 of 35
Thread Starter 
Quote:
Originally Posted by arnyk View Post

Very good chance of that:

http://www.123securityproducts.com/v...&CS_010=vid-gl

Thanks.
post #19 of 35
Thread Starter 
Quote:
Originally Posted by duvetyne View Post

It means it's old and it's failing. the power supply caps are no longer effective filters and are allowing 60 or 120 hz hum on the output.

OK. This unit is certainly a few years old. Thanks.
post #20 of 35
Thread Starter 
Well it can't be the signal booster. I disconnected it and was still getting a picture on my main TV! So I looked again and it is AFTER the split that goes to Tivo. So of course I was getting a picture!! It's to booster the signal to the bedrooms. Oops. So that was a red herring. I will call my cable provider to check the grounding outside and I have ordered a Jensen device just in case.

Also I just went outside and looked at the grounding cable between the cable and grounding cable going into the ground from the mains electrical panel. It's connected very securely. So I don't see how it could be that.

I even just tested watching a DVD and connecting and disconnecting the coax. Which of course is not even being used when watching a DVD, but Tivo would then be passing on the signal to the receiver anyway. And sure enough the hum gets very noticeable when the coax is connected and is goes (or at least all but the slightest hum that I think is probably "normal" baseline speaker hum that certainly can't be detected unless your ear is touching the speaker) when the coax is disconnected. So at this point I guess I just have to hope this Jensen device works. What else can I do?
post #21 of 35
Quote:
Originally Posted by britdiver View Post

We So at this point I guess I just have to hope this Jensen device works. What else can I do?

Get the Radio Shack ground isolator with all of the needed performance for a tenth of the price. ;-)
post #22 of 35
How does that work for coax?
post #23 of 35
Thread Starter 
Well I just had another interesting symptom. It's too much of a coincidence to be a different issue to me. Anyway, I was channel surfing and noticed to had no sound at all. So at first I just thought I had hit mute on the remote by mistake. But no. I tried a regular SD local channel. No sound. Tried digital channel. No sound. Tried HD channel. No sound. I then went to the bedroom and that tv had sound. It's not connected to any of the main system or receiver. So I pulled the HDMI cable out of the back of Tivo counted to 10 and plugged it back in......... and the sound came back. Very interesting, but I'm not sure what it proves. Who understands HDMI? I do know there is some kind of sync/handshaking that goes on between devices at either end of a HDMI cable. So is it the HDMI cable or the Tivo HDMI outlet? I'm hoping this is progress to finding the problem at least.
post #24 of 35
Hum/ground loop is probably unrelated. Chalk it up to a HDMI quirk.
post #25 of 35
Thread Starter 
Quote:
Originally Posted by Ratman View Post

Hum/ground loop is probably unrelated. Chalk it up to a HDMI quirk.

You don't think that maybe it's related and that Tivo or the HDMI cable is introducing the hum and when the coax is disconnected, as there is no audio to process it doesn't introduce the hum?
post #26 of 35
What can I tell you? Get a new Tivo and a new HDMI cable and see if it helps. I personally don't think that will resolve the "hum" issue(s). But... I could be wrong.

Go with your gut feeling to resolve the existing and additional issues you have. Sorry, but IMO, you need to troubleshoot methodically. One "problem" at a time.

I gave my suggestions/observations. Hopefully others will continue to assist.
post #27 of 35
Thread Starter 
Quote:
Originally Posted by Ratman View Post

What can I tell you? Get a new Tivo and a new HDMI cable and see if it helps. I personally don't think that will resolve the "hum" issue(s). But... I could be wrong.

Go with your gut feeling to resolve the existing and additional issues you have. Sorry, but IMO, you need to troubleshoot methodically. One "problem" at a time.

I gave my suggestions/observations. Hopefully others will continue to assist.

OK. I didn't mean to make you mad. I certainly appreciate your help and advice. You certainly know more about these things than I do. I apologize.
post #28 of 35
Not "mad" at all. No need to apologize.
Just trying to make a suggestion to not overlook the obvious and address primary issue(s).
post #29 of 35
Thread Starter 
OK. Thanks.

Here is my plan as I'm going to be out of town most of this week. By the time I get back the Jensen "filter" should have arrived. So my first step is to see if that fixes the hum. If it doesn't my next idea is to take the HDMI cable out between the Tivo and receiver and replace it with component cables and see if that resolves the issue. If neither take care of the problem I guess I will call my cable company but I'm pretty sure they will probably "blame" something inside the house meaning my wiring or my equipment. But I will give them a shot.

Does that sound like a reasonable plan?
post #30 of 35
Quote:


Well it can't be the signal booster. I disconnected it and was still getting a picture on my main TV! So I looked again and it is AFTER the split that goes to Tivo. So of course I was getting a picture!!

Do you still get hum with the booster disconnected?
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