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Help Me Debug Cable TV Problem (with Audio)
Old 02-16-2009, 10:23 AM   #1
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Help Me Debug Cable TV Problem (with Audio)

Here is an audio sample that shows the Suddenlink cable TV problem I have with one channel (CBS):

Click here to hear it.

You probably won't notice it unless you are listening with headphones. It's the background whooshing noise you hear when there's no audio in the program itself. It may seem minor, but it can be very annoying, depending on the show you are watching.

It is only present on a single channel.

Any ideas on what's going on?

The cable guy is coming out again this week. He's heard it and agrees that it's a significant problem. However, he thinks it's some kind of interference from the DVR or problem with the audio of the TV. I can rule both of those out since I can see the problem with the DVR off and unplugged, and this recording was made with the TV off. I also confirmed that the problem is there even when everything in my house is turned off (via the electrical panel).
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Old 02-16-2009, 10:42 AM   #2
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Improper ground on the plug you have the TV in? Just a guess but a cheap plug tester can tell you if the ground is improper. Also not sure of this one but the polarized plugs want the positive and negative wires a specific way - I do not know if they can be reversed and cause the problem. Can you hear it when another TV is plugged in at that location over cable?
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Old 02-16-2009, 10:43 AM   #3
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Originally Posted by OAG View Post
Improper ground on the plug you have the TV in? Just a guess but a cheap plug tester can tell you if the ground is improper. Also not sure of this one but the polarized plugs want the positive and negative wires a specific way - I do not know if they can be reversed and cause the problem. Can you hear it when another TV is plugged in at that location over cable?
Ground looping might be another possibility.

http://en.wikipedia.org/wiki/Ground_loop_(electricity)
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Old 02-16-2009, 10:50 AM   #4
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AL: here is another link to Ground Loop (deals with computers but may also apply to your situation): Ground loop basics
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Old 02-16-2009, 10:57 AM   #5
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Ground loop is a good hypothesis, but remember, it's only on one channel.

I don't have any other TVs in the house for experimenting.
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Old 02-16-2009, 11:06 AM   #6
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Al,
I looked at the file with Audacity and it looks like it is a white noise that is consistent from 22hz to about 5k where it rolls off.

If I were betting I would say that this is coming from the cable head in or somewhere on the origination side. Is this from an analog channel or a digital channel? Is your cable signal from a cable box?

When I first heard the sound I thought that a compressor limiter might be pulling up background noise but looking at the signal it looks like the level remains constant. If the problem were an ac or ground problem you would certainly hear it on all channels.
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Old 02-16-2009, 11:16 AM   #7
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Right. The signal is not from a cable box.

Quote:
Is this from an analog channel or a digital channel?
I don't know. I have a plain-vanilla analog TV purchased in 1991. How would I find that out?

I get the feeling the white noise is suppressed somewhat when there's actual audio coming through. Hard to tell, though.
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Old 02-16-2009, 11:25 AM   #8
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It sure sounds like white noise to me, I see that was confirmed by smileydog. It sounded like it was compressor pumping slightly with the audio, but that might be the brain processing, not the actual source.

I normally associate ground loops with hum, not white noise.

Are you sure this isn't in the source? It is somewhat subtle, maybe it just sounds different on your neighbor's TV?

How did you record this with the TV off and no cable box? I'm not following that.

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Old 02-16-2009, 11:41 AM   #9
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If you are using a plain-vanilla analog TV then your cable company is sending an analog channel. That means they have an actual receiver at their "head end" that receives and rebroadcast the channel on whatever channel you get it on. It might be interesting to listed carefully when local cable tv ads are playing. When the local ads are running the signal comes from a local source that switched and controlled at the central cable head end. If you problem does not exist during a silent period of the local commercial then the problem could be from their network feed. If the problem is the same it could be in the equipment used to rebroadcast the signal through the cable system.

Sure sounds like it's not your tv or dvr...

Just for the heck of it - download that freeware Audacity and look at the signal - the noise is consitent on left and right - the level remains constant.

One other thought... On one of my tv's it has a feature meant to keep sound at a consitent level (to fight the occational extra loud commercial). This type of feature can sometimes bring up low volume sounds / noise during quite periods. Don't know if this could be an issue - likely not since you said it happens on with TV off and just on one channel.

Can you receive this CBS channel with antenna to compare? And if you can - surely the cable company puts the CBS station on a channel different from the broadcast channel to avoid interference.
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Old 02-16-2009, 12:16 PM   #10
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Quote:
download that freeware Audacity and look at the signal
Right. I've got that.

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Are you sure this isn't in the source? It is somewhat subtle, maybe it just sounds different on your neighbor's TV?
I absolutely think it is in the source. But I have to convince the cable company of that. It can be difficult to hear at times, based on the real audio, so I might have missed it on the neighbor's TV, but it's hard to tell.

The cable guy thinks that if everyone were hearing this, there would be lots of complaints. OTOH, DW never noticed it until I pointed it out.

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How did you record this with the TV off and no cable box? I'm not following that.
We don't have a cable box, just the coax cable from the wall. I set up the DVR to record, then turned off the TV. It recorded the show. I then sent the audio from the DVR to my computer mic/line in, played back the recorded show on the DVR, and recorded it using Audacity.

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Can you receive this CBS channel with antenna to compare?
No, we're too far away.

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If you problem does not exist during a silent period of the local commercial then the problem could be from their network feed.
Good idea. I just checked it out, and the noise is present even during the short "You're watching Cable 17, Eureka" spot just before returning to the TV show.
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Old 02-16-2009, 01:42 PM   #11
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Sounds like you've got some convincing to do. Squeeky wheel get's the grease. Keep on em!
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Old 02-16-2009, 01:58 PM   #12
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Originally Posted by TromboneAl View Post

We don't have a cable box, just the coax cable from the wall. I set up the DVR to record, then turned off the TV. It recorded the show. I then sent the audio from the DVR to my computer mic/line in, played back the recorded show on the DVR, and recorded it using Audacity.
OK, that means that two different receivers (DVR, TV) both pick up the same noise. More evidence that it is the source, not the receiver.

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The cable guy thinks that if everyone were hearing this, there would be lots of complaints. OTOH, DW never noticed it until I pointed it out.
Well, you are a musician. Your ears will pick up things that others don't.

It's a blessing and a curse, as I'm sure you know.

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Old 02-16-2009, 03:17 PM   #13
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Late to this party...

Sounds to me like AGC (automatic gain control) bringing up the noise floor. Noise seems to drop when audio ,signal is present (talking) noise rises with silence. Most likely at the cable operator's receiver for this particular channel, then feeding it into the cable.

Definitely not grounding issue. Two different devices exhibiting same noise does point to cable co problem.
Agree the curse of musician's ear, or that of a techie. It would drive me buggy, DW would be wondering what my problem is.
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Old 02-16-2009, 06:37 PM   #14
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Hmmm...buy a tv built in this millenium?
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Old 02-16-2009, 06:49 PM   #15
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Well, two cable guys came today. They heard the problem and agreed it was significant. They changed connectors, etc, but that made no difference. The problem was much less noticeable on their little 13 inch TV -- I think it's because there's very little bass on that -- who knows?

I gave them a DVD with a soap opera recorded on it (the problem is most noticeable with these programs), and an audio DVD with the above sample. They are going to look into it some more.
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Old 02-17-2009, 05:28 PM   #16
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To finish up this thread: Someone called from Suddenlink to tell me that they could not hear the problem at their end, although they listened carefully, with headphones, etc. He suggested that perhaps the bass or other controls are set high on our TV. Note, however, that the problem can be heard when a show is recorded on the DVR.

So, I'm not pursuing it any further. It's not too much of an annoyance, and when we get a new TV, it will probably go away.
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