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Old 01-26-2014, 05:20 PM   #1
marklyn
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Occasional and infrequent sound blips and light pixelation; how to diagnose?

I am occasionally noticing some very slight pixelation followed by an occasional sound 'blip'. I'm not sure if it predominately happens on one or more channels, but when I caught it happening on one of my local channels I went to the diags screen and all tuners showed mid-high signals (93-100).

How does one methodically try to figure this out. If someone can provide me with some ideas, I'd like to figure out why.
I also should mention that my SNR numbers are usually 39-40ish range, but I haven't paid as much attention to that as the signal strength. Should I?

Would a cable booster improve the issue or would it also boost any problems that might be involved?

My cable comes into my attic and splits 3 ways (1 to AV cabinet, 1 to cable modem and 1 to 4 way spitter)

The AV cabinet has a 2 way splitter, 1 to tuning adapter and 1 to Tivo.

Cable is about 5 years old but heavy duty and was used for satellite install.
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Last edited by marklyn : 01-27-2014 at 08:20 AM.
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Old 01-26-2014, 06:20 PM   #2
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The absolute first thing I would do is when it happens, hit the replay button and re-watch the segment. If it's a consistent issue at the same spot, it's a signal issue. If it disappears on replay, you could be looking at a hard drive issu or other hardware problem.
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Old 01-26-2014, 10:49 PM   #3
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According to a recent call I had with Tivo support, they want the SNR in the 32-35 range and anything higher is "too hot" as they termed it.

You could check to see if the splitter at the Tivo was the issue by removing the splitter and using the OUT side of the tuning adapter to feed into the TV. It'd not the preferred solution, though would work to see if the splitter is the issue.
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Old 01-27-2014, 07:02 AM   #4
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Originally Posted by shrike4242 View Post
According to a recent call I had with Tivo support, they want the SNR in the 32-35 range and anything higher is "too hot" as they termed it.

You could check to see if the splitter at the Tivo was the issue by removing the splitter and using the OUT side of the tuning adapter to feed into the TV. It'd not the preferred solution, though would work to see if the splitter is the issue.
My SNR's have always been over 35 as far as I know. What does the term 'too hot' mean and how does one fix something too hot?
Is that related to signal strength?
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Old 01-27-2014, 07:23 AM   #5
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I had a similar issue not too long ago where the picture would suddenly pixelate and the sound would garble. It would occur on two different TVs with Tivos at the same time so we (TWC and I) ruled out the Tivo. TWC had to hook up a meter at the post by the street to verify it was coming from outside my house. They saw it too. They had to locate and repair some of their boxes along the line. The only way they were able to diagnose this was to be there an see it when it was happening. May or may not be what's happening on yours, but if they can't find a problem inside your house, you'll have to work with them to find it somewhere along the line to your house.
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Old 01-27-2014, 07:43 AM   #6
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First, it's "SNR" (signal-to-noise ratio) not "SNL" (Saturday Night Live).

Too hot normally would mean your signal strength is too great, so it's overloading something in your tuner circuitry. In principle there should be no such problem as too high a SNR value --- high SNR is generally good. So why does Tivo support always talk in terms of SNR being too high (rather than signal being too high)? I think it's because the signal strength reading in Tivo diagnostics is not useful for detecting excess signal levels --- because it pegs at 100 (while the actual strength might be much greater). Thus I think Tivo uses high SNR as a proxy for high signal strength. Probably this is partially correct. In situations where your Signal Strength is pegged at 100 a SNR or 37 or higher may mean the Signal Strength is too high.

I, and I suspect many others, have many channels that have SNR's or 36 or greater and that have no problems at all.

Reducing signal strength (and probably also SNR) is easily done with in-line coaxial attenuators that sell for a few bucks, for example:
http://www.amazon.com/gp/search/ref=...qid=1390829965
A selection of one each of 3, 6 and 10 dB should give you a lot of flexibility. You can put them in series, e.g., 3 and 10 in series gives 13 dB.

Ideally you should get ***all*** your channels in the 80 - 99 range of signal strength recommended by Tivo on their support pages (not 100 because you don't know what that really means). There is too much "tilt" (variation with frequency) on my system to allow this so I have to compromise with many channels pegged at 100, in order to get my weakest channels up around 80.
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Old 01-27-2014, 08:03 AM   #7
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Before doing all that, follow the advice from post #2. Both easy and effective to figure out if you have a hardware issue or something else.

I had something similar a few years ago, and a reseating of the cablecard is what fixed things.
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Old 01-27-2014, 02:43 PM   #8
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The absolute first thing I would do is when it happens, hit the replay button and re-watch the segment. If it's a consistent issue at the same spot, it's a signal issue. If it disappears on replay, you could be looking at a hard drive issu or other hardware problem.
ok, so I'm thinking this through and it seems to me that if you're watching live or recorded TV that hitting replay has the same effect, no?
When you're watching live tv, Tivo is always recording so the 'blip' would have been recorded on disk (for up to 30 mins). When you're watching recorded tv, again, the 'blip' is recorded. In both cases, wouldn't rewinding in both cases and seeing the blip in the same segment mean the same thing?

When this happened, I did press the replay button and the blip was consistent in the each scene that I initially saw it.

Should I also start to make note of which channels this happens on and what time or is that necessary.
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Old 01-27-2014, 02:59 PM   #9
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Yes, anything you watch from a Tivo is off the hard drive, so rewinding Live TV or a recorded program is the same thing. The key point is that the error is the same. A common symptom of pending hard drive failure is intermittent read failures, which manifest as pixelation/sound blips. It's unlikely since you're using a new Roamio, but still possible and easy to test for.

Since the blips are in the same spot, it would appear to be a signal issue. At this point, I would try to track any similarities in when you see the problem. Perhaps it's on the same few channels. After a Live TV event, you can also go into Settings -> Account and System Info -> DVR Diagnostics and find the tuner in use for that channel and note the frequency on which the channel is broadcast. With SDV, the Frequency used for some channels, can change from day to day so the pattern may be a range of particular frequencies and not necessarily the same channel numbers.
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Old 01-27-2014, 05:14 PM   #10
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OK, so I've done a bit more investigating and I've come across 3 channels (two locals) that occasionally 'blip' and when I rewind the blip is still there.
The signal strength for these channels is usually 99-100 and the SNR is usually 39-41ish, both consistently.

Additionally, I have come across 5 channels like all the VH1 channels and at least two other high number channels that will tune in for about 4 seconds and then go to a "This channel is temporarily unavailable. Press select to try tuning to this channel again".
Pressing select only re-tunes it for another 4-5 seconds before the message reappears.
Incidentally I checked the SNR and signal strength for these channels and it is consistently a signal strength of 73-82 (at most) and SNR is around 32ish.

Thanks for the troubleshooting tips so far. Anything else I can check or look for? Is it time for me to call TWC out or do I need to gather more evidence so they don't automatically blame the Tivo?
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Old 01-28-2014, 02:08 PM   #11
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Resolved! coax splitter to blame!

After another call to TWC cable card folks, they had me check the tuner signal levels (dB and he noted they were at -11 and -12. He said the range should be between -7 and +7, more in the center is the best.
I did some troubleshooting and, among other things, I removed a 2 way splitter in my AV cabinet and routed the inbound (hot) cable to the tuning adapter and then the output of the tuning adapter now goes to my Tivo. (initally the splitter sent a hot signal to the TA and one to the Tivo).

Now on my Tuning Adapter/Tuning adapter diagnosis screens, under status summary my levels have improved. They were -11 and -12 and now are -5 dBmv (for Tuner).
My FDC stayed the same at zero and my RDC is at 42. The cable card guy said these are now 'perfect' settings. He sounded happy.

So far the sound 'blip' and slight pixelation has not recurred (keeping fingers crossed).

Also, all of my signal strengths, especially on channels were it was 73-78 have all moved up to very respectable levels. My lowest one I found was 83 (so far).

I guess the bottom line is that the second splitter in the AV cabinet was enough to degrade the tuner dBmv but it wasn't enough to lower my signal strength too much (which was always in the 90's). That's why it's confusing to me, I went only on signal strength for the channels I was having issues with. Looks like I need to pay attention to the dBmv numbers too.
If anyone can provide a basic explanation of two sets of numbers and how they may be related, I'd like to know.
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Old 01-28-2014, 02:39 PM   #12
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Whenever the FDC gets beyond +/-8, I've always experienced failure to tune the SDV channels. Get channel not available. Not sure I noticed pixelation also.
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