A mysterious TV phenomenon

[Buzz Bloom]

TL;DR Summary

I witnessed a friend’s television exhibiting some very strange behavior. I am hoping someone at PFs will have an idea about the cause.

The odd phenomenon only occurs on programs from MSNBC. The audio and video are annoyingly not in sync. The video lags the audio with variable lag times estimated between 200 ms and 600 ms.

The following is some technical information about the television and the attached combination tuner-VCR box. I have no idea whether this will be useful to any reader.
Television: Sharp 70” Model #LC-70C7500U
Tuner/VCR: Motorola Model DCX-3400

 

[Baluncore]

Start here...
https://www.sony.com/electronics/support/articles/00026069
https://www.techwalla.com/articles/how-to-fix-out-of-sync-audio-video-on-tv

 

[berkeman]

Summary:: I witnessed a friend’s television exhibiting some very strange behavior. I am hoping someone at PFs will have an idea about the cause.

The audio and video are annoyingly not in sync. The video lags the audio with variable lag times estimated between 200 ms and 600 ms

Was it for some reporting where the reporter could be using their cell phone or some other improvised method because of the pandemic distancing thing? I've seen it a few times for reporters and commentators who were on some improvised connection means...

 

[Buzz Bloom]

Was it for some reporting where the reporter could be using their cell phone or some other improvised method because of the pandemic distancing thing? I've seen it a few times for reporters and commentators who were on some improvised connection means...

Hi berkeman:

No. The phenomenon is present for a variety of talking head presentations by regular presenters.

Regards,
Buzz

 

[Tom.G]

That is common for videos transported over the Internet. At least the players, and maybe the protocol, prioritize the audio stream when there is congestion (delays). Chopped up audio is quit uncomfortable to follow, whereas a few dropped video frames are at worst annoying.

The other effect you may notice is the delay between the asking of a question and the response. That is network latency.

A similar latency problem can occur with voice calls that are routed thru a communications satellite. If at all possible the satellite routing is only one way, with the other path being terrestial. That's because the round trip satellite delays are enough to trigger humans into thinking something didn't get thru, then we start to oscillate!... talking over each other.

Cheers,
Tom

 

[Vanadium 50]

The odd phenomenon only occurs on programs from MSNBC. The audio and video are annoyingly not in sync. The video lags the audio

Does it go the other way on Fox?

 

[Buzz Bloom]

Does it go the other way on Fox?

Hi Vanadium :

I see the wink, but I am unsure of the joke. Anyway, only MSNBC displays the mystery.

Regards,
Buzz

 

[dlgoff]

Summary:: I witnessed a friend’s television exhibiting some very strange behavior. I am hoping someone at PFs will have an idea about the cause.

The odd phenomenon only occurs on programs from MSNBC. The audio and video are annoyingly not in sync. The video lags the audio with variable lag times estimated between 200 ms and 600 ms.
... attached combination tuner-VCR box. I have no idea whether this will be useful to any reader.

bold by me

More than likely the delay is happening within the tuner-VCR box.

 

[Vanadium 50]

but I am unsure of the joke.

MSNBC is considered left-leaning politically, and Fox is considered leaning the other way.

Anyway, @Tom.G has it right. Audio and video packets are sent with different priority.

 

[sophiecentaur]

Frankly I think the delays and dropouts are unacceptably bad. Unacceptable for me but acceptable for the operators because it has to be down to how much money the broadcaster is prepared to spend on their links.

When we started using Skype and its descendants for our family and social contacts, we were impressed and it was FREE so we accepted all sorts of glitches. That doesn't excuse the commercial users from subjecting us to delays and glitches on links between and within cities as if we were listening to a reporter embedded in the front line in a Middle East conflict.

I used to work for a National Broadcasting Service and nothing but nothing in the way of service interruption was accepted without an 'investigation' and rapped knuckles.

 

[Buzz Bloom]

More than likely the delay is happening within the tuner-VCR box.

Frankly I think the delays and dropouts are unacceptably bad.

Hi digoff, sophie, and @Baluncore:

I sent the advice from this thread to my friend, and he did some experimenting. He took the recorder box out of the signal flow, and the lag stopped, but he has not been able to fix the lag when the recorder is attached.

So the problem is in the recorder, but it also remains a strange phenomenon that the problem is only present when watching MSNBC.

Regards,
Buzz

 

[Fred Wright]

My theory: The recorder firmware is triggering an exception because of codec header mismatch (not seeing the header it expects).

 

[dlgoff]

Summary:: I witnessed a friend’s television exhibiting some very strange behavior. I am hoping someone at PFs will have an idea about the cause.

The video lags the audio with variable lag times estimated between 200 ms and 600 ms.

I'm wondering if there is a delay due to tape head"flanging".

At the 38 cm/second tape speed, the distance between record head and the typical analogue tape recorder introduced a fixed delay of about 35 ms. The precise delay depends on the configuration of the record and playback heads.

 

[sophiecentaur]

So the problem is in the recorder, but it also remains a strange phenomenon that the problem is only present when watching MSNBC.

I have a Denon sound 'receiver' that I use for the surround sound system for my TV. One of the adjustments you can make is +- Audio Delay. Occasionally I need to ' help it' by pressing the buttons. It's clearly a known phenomenon and it must depend on the way sound and vision signals are coded and on what sense (if any) the decoder makes.

In the early days of Colour TV there was no possibility of compensating for the different arrival times of different video signals from different sources unless they all synced to one source signal. Independent TV companies needed breaks for adverts, every 15minutes of so. The distributed program signals and the adverts came from different places in the country and the timing change was very noticeable. So they introduced a white 'exploding' star logo, which was screened during the changeover between national ads and regional programs. A solution in the way of an analogue video delay of more than a few microseconds was too expensive.

The BBC Television Centre was built in the form of a circle, with the signal routing equipment sited underground at the centre of the circle. All equipment was synched to a timing source at the hub (same length of cables) and, likewise, the signals from all the studios would turn up at the hub, synchronised so you could switch from studio to studio with no glitch. The timing error to get the colour subcarrier phases right was critical so the cabling needed to be right to within only a few feet. A great example of 'the tail wagging the dog'.

Later, the (cheap) digital field store was invented and the delay problem was solved.

 

[Buzz Bloom]

I'm wondering if there is a delay due to tape head"flanging".

Hi digoff:

Would the tape head have an influence when just watching television whose cable signal passed through the tuner-recorder box. That is, no tape was playing?

Regards,
Buzz

 

[sophiecentaur]

Would the tape head

This tape head is not recording analog audio signals. We are in a digital world and all the data that's recorded is digital and at a much higher rate (despite a lot of bit rate reduction) than 'flanging' could affect in a subjective way. The coding and modulation that's used in digital recording is 'appropriate' for the data it's designed to handle.

If you are actually discussing analogue TV then the sound would be on a subcarrier.

 

[Buzz Bloom]

Hi @Baluncore, @berkeman, @Tom.G, @Vanadium 50, @dlgoff, @sophiecentaur, and @Fred Wright:

I thank you all again for your contributions to solving this puzzle. My friend just emailed me a new clue.

In the past, the phenomenon of out of sinc sound and picture on MSNBC was when it was watched directly from cable. Now the phenomenon was seen when watching MSNBC via the internet. The conclusion is now that the phenomenon has nothing to do with the method of reception. Rather it is a feature of MSNBC broadcasting.

Regards,
Buzz