Random LFE Thumps - NBC Network Broadcasts Only!

Originally Posted by howardru 

Having this extremely strange audio problem. At first I thought my subwoofer was failing but convinced it's something inside the Dolby Digtal audio track of the encoded HD signal.

Some Key A/V Info:

- Tivo HD Series 3 HDMI connected to receiver. Audio Setting on Tivo: Dolby Digital

- Onkyo NR-709 Receiver with 7.1 Surround speakers. Audio Setting: Dolby Digital Expanded

- Panamax 5400 filtering power and HFC cable TV Signal


With the local NBC Affiliate here outside Boston, I am receiving random audio LFE thumps from my subwoofer ONLY during Network broadcasts, NOT the local NBC affiliate broadcasts (WHDH in Boston). The problem ONLY happens during NBC Today show, NBC Nightly News, Presidential Election night. NEVER during any other local or network broadcast on any other HD Channel.

Facts:
- Thumps can be heard in same scenario with HFC cable connected directly to clear QAM Tuner TV card in my PC. This tells me it's not the Tivo.

- Thumps occur in the same scenario with HFC cable connected directly to my Samsung LED TV using clear QAM tuner inside TV Set. This tells me it's NOT the Tivo.

- Random thumps ARE recorded on the Tivo. I can play them back to the cable company when they are here to diagnose the problem.

- Cable company came in and tested the QAM frequency (607) and it's clear and almost error free.


I contacted the NBC affiliate in Boston regarding this problem but they weren't aware of the problem. Had the local cable company out here and inquired if the "Network" broadcast feed was coming in via satellite and being re-encoded and spliced locally with the Boston affiliate station. Nope, they only have one signal off the satellite and they do no encoding or re-modulation.

What I DID find: Whatever is encoded in the original Audio track coming into my Tivo is "filtered out" when I set the Tivo to down convert to PCM. In this mode, I can't run Dolby Digital Expanded, audio sounds OK but I am stuck on THX Cinema.

This problem doesn't happen on ANY other HD channel that I might watch. FOX, CBS, ABC etc...ONLY NBC and ONLY during Network originating broadcasts.

Suggestions Anyone? Grasping at straws here.

Originally Posted by howardru 

Thanks for the advise and responding.

Maybe my explanation sounded intelligent, but my knowledge is limited here in the audio stream.

How, where and what piece of electronics am I looking to buy? Is there some frequency that I should be specifying to filter out? Can you provide a URL to Amazon or some electronics store that I can get an idea as to what you are referring to?

Originally Posted by howardru 

Having this extremely strange audio problem. At first I thought my subwoofer was failing but convinced it's something inside the Dolby Digtal audio track of the encoded HD signal.

Some Key A/V Info:

- Tivo HD Series 3 HDMI connected to receiver. Audio Setting on Tivo: Dolby Digital

- Onkyo NR-709 Receiver with 7.1 Surround speakers. Audio Setting: Dolby Digital Expanded

- Panamax 5400 filtering power and HFC cable TV Signal


With the local NBC Affiliate here outside Boston, I am receiving random audio LFE thumps from my subwoofer ONLY during Network broadcasts, NOT the local NBC affiliate broadcasts (WHDH in Boston). The problem ONLY happens during NBC Today show, NBC Nightly News, Presidential Election night. NEVER during any other local or network broadcast on any other HD Channel.

Facts:
- Thumps can be heard in same scenario with HFC cable connected directly to clear QAM Tuner TV card in my PC. This tells me it's not the Tivo.

- Thumps occur in the same scenario with HFC cable connected directly to my Samsung LED TV using clear QAM tuner inside TV Set. This tells me it's NOT the Tivo.

- Random thumps ARE recorded on the Tivo. I can play them back to the cable company when they are here to diagnose the problem.

- Cable company came in and tested the QAM frequency (607) and it's clear and almost error free.


I contacted the NBC affiliate in Boston regarding this problem but they weren't aware of the problem. Had the local cable company out here and inquired if the "Network" broadcast feed was coming in via satellite and being re-encoded and spliced locally with the Boston affiliate station. Nope, they only have one signal off the satellite and they do no encoding or re-modulation.

What I DID find: Whatever is encoded in the original Audio track coming into my Tivo is "filtered out" when I set the Tivo to down convert to PCM. In this mode, I can't run Dolby Digital Expanded, audio sounds OK but I am stuck on THX Cinema.

This problem doesn't happen on ANY other HD channel that I might watch. FOX, CBS, ABC etc...ONLY NBC and ONLY during Network originating broadcasts.

Suggestions Anyone? Grasping at straws here.

Originally Posted by arnyk 


Add a high pass filter to the segment of the signal chain that is giving you the thumps. There's a high probability that you aren't receiving anything really ugly via your TIVO, but that the subsonic response of your system is tipped up quite a bit, and turning rapid temporary losses of signal or subsonic disturbances into more than they started out to be. A lot of people are finding that if they put a high pass fitler in line with their subwoofer so that it only sees signals that it can respond to cleanly, the sound quality of their system is greatly improved.

Originally Posted by howardru 

I have a Polk DSW Pro 600....I'm not seeing it in the specs, would you happen to know if Polks has this?

http://www.polkaudio.com/products/dswpro600

Originally Posted by arnyk 


From the owner's manual (online)



Short answer: no subsonic filter visible.

Originally Posted by J_Palmer_Cass 





That is a ported subwoofer, so it most likely has a fixed high pass filter near the 20 Hz area.