Hi, I resisted posting this for a while hoping it would get cleared up but it hasnt. For about a week now, certain CBS shows have a terrible audio lag. The video moves much faster than the audio, so there's no way to correct it on site. I've noticed this on Letterman, "how i met your mother", NCIS, etc. is anyone else seeing this as well? in our local HDTV thread it has been mentioned, but I'm wondering if its a national issue as well.

KDKA-DT (Pittsburgh CBS O&O) has had an audio lag on CBS network programs for years. Sometimes it's worse (longer delay) than others. This has been observed by OTA viewers as well as cable. They don't seem to care enough to fix it.

Agreed. I am in Butler, 35-40 miles north of Pittsburgh. Last night, Criminal Minds was off with different degrees. Sometimes it was just slightly and other parts of the show was very noticeable. I use Armstrong cable and the problem was only that channel. It happens fairly often :mad:

I'm in Shreveport, Louisiana and CBS OTA does the same for me. Some nights it's not off that badly but other nights it's just terrible. It's definetly a nationwide problem.

Typically it is a video delay; that is, the video is lagging behind the audio, so you hear the word before the actor's mouth moves.

Was getting it really bad on Letterman out of Rockford, IL a few weeks back for about a week straight. Really don't watch the network otherwise, and I thought it just might be that show on that station, but someone, somewhere else reported the same issue at the time.

Typically it is a video delay; that is, the video is lagging behind the audio, so you hear the word before the actor's mouth moves.


its not video delay, i wish it were, i could correct it. The audio is lagging behind the video, for sure. a lot of receivers/processors have audio time delay adjust, i thought it might be the audio and adjusted it, but it made the lag worse, so its defnitely not the audio. whatever it is, its made CBS completely unwatchable for me.

never seen it here locally. WLTX-DT

I've been complaining about this for over a year. It is definitely the audio lagging behind the video. I've seen this on Letterman and several ABC shows such as "Desperate Housewives" and "Grey's Anatomy." I have Comcast cable in Seattle. My friends with OTA also have this problem. It is clearly evident at the end of Letterman when the last segment often switches back to SD with pillar boxes. The sound is immediately spot on during this brief segment.

Let's all keep complaining.

No lag in Denver.

I recently sent an e-mail to our local ABC affiliate, KOMO regarding this audio synch issue. Here's the reply:

Thanks so much for you e-mail.

Unfortunately, we had to install a new encoder last week that knocked the lip sync out of whack a bit.

We have made adjustments and I think that you will find that if you re-scan your TV’s add Channels you will notice a marked improvement.

I apologize for this but from time to time these things happen.

It is a tough thing to try to make even the smallest adjustments without cascading effects down the line.

Every decoder acts a little differently.

Please let me know how it comes out for you.



Respectfully,


I did notice that "Ugly Betty" looked good last night. I'll keep you posted. I think I'll write our CBS affiliate today.

whoa, good for you and your local ABC affail for responding. I tried to watch Shark last night and couldnt, it was so ridiculous. I think i'll take your advice and call the engineering dept of CBS. lets hope i get an answer here.

I guarantee that it is not national. The satellite feed that the stations get has perfect sync. Our local CBS station here in Colorado Springs sends it out in perfect sync as well. Complain to your local station.

Our fox station had horrible sync when the first went digital but eventually fixed it.

Roy

our local CBS affail has been really good. i cant believe they would do this now. They even do the local news in HD, and constantly brag about it... and the audio on the news is synched just fine. up until a week ago so was the national feed. unbelievable.

CBS HD network 5.1 audio is sent as Dolby E. The affiliates use Harris HD satellite receivers. For proper lip sync the receiver's delay offset for the Dolby E stream needs to be set to -33 ms which is 1 video frame advance. This compensates the 1 frame delay that the Dolby E decoder adds. There is also a 2.0 stereo stream for stations not equipped with 5.1, and the offset for that stream should be 0 ms.

The transmitted 5.1 from all HD stations is AC3. The encoder used is usually a Dolby DP569. It has a delay of 187 ms which is nearly 6 frames. This delay needs to be compensated for in the HD encoder. Some encoders use a numerical entry to control the offset, while others like the older Motorola required time code stamping.

I've been e-mailing our local CBS affiliate KIRO in Seattle. I'd like to send them this information from RSF-LA. However, I'm wondering if we are talking about the same type of problem. Here, most of the regular network shows are synchronized pretty well. On "The Late Show with David Letterman" the video comes BEFORE the Audio. Dave's mouth moves and then you hear him. Is this the same problem that the Dolby E adjustments address?

Thanks.

Probably not as this setting probably wouldn't changed at the station program to program. I'm only guessing, but one possibility is that they are doing their own delay for Letterman and that is causing a problem. I'll try to remember to watch Letterman here to see if it looks in lip sync.

Probably not as this setting probably wouldn't changed at the station program to program. I'm only guessing, but one possibility is that they are doing their own delay for Letterman and that is causing a problem. I'll try to remember to watch Letterman here to see if it looks in lip sync.

I would have sworn there were some lip-sync issues with Ghost Whisterer this Friday also, didn't notice any on Numb3rs though.

I usually watch Letterman on KPIX via DirecTV -- the lip sync is way off (audio lags video). I recorded a piece of the show and ran it into my PC -- I had to move the audio ahead 4 frames before it appeared to be in sync.

When KPIX runs local material, the sync is fine, so it's not a DirecTV issue. I also receive KCBS and have checked it there -- it may not be dead-on, but it's a lot closer.

When KPIX runs local material, the sync is fine, so it's not a DirecTV issue. I also receive KCBS and have checked it there -- it may not be dead-on, but it's a lot closer.Have you noticed lip sync problems on KOVR, or on KPIX with other shows?

CBS HD network 5.1 audio is sent as Dolby E. The affiliates use Harris HD satellite receivers. For proper lip sync the receiver's delay offset for the Dolby E stream needs to be set to -33 ms which is 1 video frame advance. This compensates the 1 frame delay that the Dolby E decoder adds. There is also a 2.0 stereo stream for stations not equipped with 5.1, and the offset for that stream should be 0 ms.

The transmitted 5.1 from all HD stations is AC3. The encoder used is usually a Dolby DP569. It has a delay of 187 ms which is nearly 6 frames. This delay needs to be compensated for in the HD encoder. Some encoders use a numerical entry to control the offset, while others like the older Motorola required time code stamping.
Just to keep things in perspective, there is a lot more delay in the video encoder than there is in the audio encoder. "Advancing" the audio really means not delaying it so much so it matches up again with the picture. Also remember that, in MPEG, video frames are usually sent out of order, so lots of video delay is required. Time stamps (not the same type as the Motorola encoder uses) are what makes the system have even a prayer of working.

Funny how we always assume it is an audio problem...

I would have sworn there were some lip-sync issues with Ghost Whisterer this Friday also, didn't notice any on Numb3rs though.

i've seen lipsync issues with all CBS programs all this week on WTVF. something is definitely wrong

Just to keep things in perspective, there is a lot more delay in the video encoder than there is in the audio encoder. "Advancing" the audio really means not delaying it so much so it matches up again with the picture. Also remember that, in MPEG, video frames are usually sent out of order, so lots of video delay is required. Time stamps (not the same type as the Motorola encoder uses) are what makes the system have even a prayer of working.

Funny how we always assume it is an audio problem...The audio stream is muxed with the encoded video in the video encoder, and it's the video encoder that keeps the audio in sync. Different audio codecs have different delays. If an external audio encoder is used such as a DP569 for AC3 (187ms), the encoder needs to be set to compensate for that delay. There are different approaches to setting the delay compensation on Dolby E. It can be done in the video encoder, the receiver or split between the two.

The audio stream is muxed with the encoded video in the video encoder, and it's the video encoder that keeps the audio in sync. Different audio codecs have different delays. If an external audio encoder is used such as a DP569 for AC3 (187ms), the encoder needs to be set to compensate for that delay. There are different approaches to setting the delay compensation on Dolby E. It can be done in the video encoder, the receiver or split between the two.
The audio data is inserted into the transport stream by the multiplexer, just as the video data, captioning, and PSIP data is. Strictly speaking, it is not passed through the video encoder (video data rate reduction process.) Whether the "encoder" uses an internal AC3 encoder or an external one, the delay of audio encoding is the same. (Other audio encoding systems do have different delays.) The "multiplexer" needs to know that the audio was compressed externally and to stamp the incoming data with the proper time stamp.

When considering lip sync, generally speaking, encoder delays are compensated for in the encoder and decoder delays are compensated for in the decoder. Otherwise, interoperability between (or among) MPEG codec manufacturers becomes a hassle. Sometimes the audio is "delayed" so that it is in sync when it is decoded.

None of this really explains where the lip sync error is. I'm sure CBS has their audio in sync. They work very hard to make it that way and keep it that way. The problem is most likely in the local station.

Interesting. I can't say I've used every encoder, but all the ones I've used encoded both video and 2 ch. mpeg/ac3 audio. If an external audio encoder is used the stream was sent to the encoder. I've not seen encoders that required an external muxer to add audio. Even the early (huge) Mitsubishi/Tektronix encoders muxed external audio internally. AFAIK CBS network uses Harris encoders, and the video/audio muxer is part of the encoder. Lip sync is controlled by audio timing offset settings in the encoder.None of this really explains where the lip sync error is. I'm sure CBS has their audio in sync. They work very hard to make it that way and keep it that way. The problem is most likely in the local station.I agree, but it's interesting that some shows are in sync and others are not. That still doesn't rule out local problems.

Have you noticed lip sync problems on KOVR, or on KPIX with other shows?

I must admit, I haven't done any real "studies" of this situation, other than the one I mentioned where I attempted to document the severity of the error on Letterman as viewed on KPIX. I have a couple of CBS prime shows (recorded from KPIX) sitting on the DVR, and upon a quick check, it appears as though the sync is not perfect, but closer than it is during Letterman. Which is to say, it's close enough to be tolerable. Might this have something to do with different signal paths, as the prime shows were 5.1, but Letterman is not?

This week, I will attempt to document the amount of delay present on the three CBS stations I can receive. I will check them all during a prime 5.1 show, and during Letterman. Stay tuned for the results ...

And here they are:

Observed tonight's CSI: Miami on both an HR10-250 (DirecTV HD TiVo) and an HR20 (DirecTV HD DVR) from three different sources. The most interesting find of the night was that the audio on the HR20 is already disadvantaged, as it is lagging by 40 ms (just over a frame) compared to the HR10. Viewing the three stations, the results were:

KOVR (OTA) - Dead-on sync
KPIX (DirecTV HD Local feed) - Dead-on sync*
KCBS (DirecTV HD DNS feed) - Audio lagged by 1-2 frames

*After discounting the 40ms delay added by the HR20

On Late Show with David Letterman, the results:

KOVR - Audio lagged by 1 frame
KPIX - Audio lagged by 2 frames
KCBS - Audio lagged by 2 frames

Note that when viewed on the HR20 (which is the only way to see the KPIX feed), you can add another frame to those observations, which pushes Letterman to a 3 frame lag on both KPIX and KCBS, which is pretty uncomfortable.

I arrived at those figures by recording the output of the DVRs to a Panasonic DVD-RAM recorder, loading the file into a PC, opening the file with Video Redo, then adjusting the audio synchronization until it looked right to my eye. It was easier to get a pretty exact reading on Letterman, as there are many precise "sync" markers, such as when he slaps his hand on the desk.

Not sure what to do with this information, but there it is ...

Interesting that Letterman is different than primetime.

I have noticed no such issues with KYW in Philadelphia which has dead on sync.

I have seen this problem on WTVF Nashville and WHNT Huntsville. I am to the point where I surf the net while I watch Jericho so I only see the TV out of the corner of my eye. Audio synch problems are very annoying!