Digital Cable Sound Delay on my HTIB?!?!?!?!

[mohakky]

I just hooked up my Motorola DCT2500 digital cable box to the aux in on my Koss 4102 HTIB. Im using Composite Video In and Coax Digital Sound In ... Video is output Composite Video, Sound obviously goes through the 5.1 speakers.

When I try to watch anything on the TV from the cable box theres a LAG of about 1-2 seconds between the video and the audio....

WHY is this happening? is my cable box misconfigured? need a firmware update? need a newer box? my HT screwed up? ANYTHING???

Thanks

[edtyct]

Lip sync problems like this one can have a number of causes. The obvious ones are the amount of processing that video signals endure along the chain right through to the STB and MPEG compression delays, which vary according to the complexity and motion of the image displayed. Many digital processors, including DVD players and STBs, have an automatic and/or manual lip sync adjustment. Apparently, your Motorola 2500 doesn't, being, I take it, an older model. I don't know whether a firmware upgrade is available for it. It's worth a try. By the way, why aren't you using the component output from the digital STB? Assuming that your TV can accept it, it will improve your picture.

Ed

[NickJ]

Lip-sync errors caused by the video being delayed allowing the sound to get "ahead" by as much as several video frames is widespread. Broadcasters themselves are often responsible for a frame or two of video delay (which varies from time to time) and when equipment in your home theater like scan converters and slower LCD or Plasma displays adds another frame or two the sound occurs so much "before" the video lip movement that it becomes "very" noticeable.

Sound never occurs "before" the event producing it in nature. All sounds we observe in nature reach our ears "after" a delay of approximately one ms per foot of distance the originating point is away from our ears and our brains are accustomed to factoring that in as “distance” information. At the ball field you see the bat hit the ball well ahead of the loud “crack” reaching your ears - perhaps even a few hundred ms if you are that far away - and our brains are perfectly happy with that natural phenomenon. This makes the "physically" impossible condition of sound “leading” the visual image which produced the sound “jolt” our senses. (i.e. - hearing that loud crack “before” the bat hits the ball)

Most industry publications state that a consumer can not detect out of sync conditions fewer than 50 ms but I can confirm from my experiments that is simply not the case. Perhaps it may take that much video delay to "initially" attract attention to this problem but once you are bothered by it and have a way to correct it achieving perfect sync, you will be able to see out of sync conditions as small as even "ONE" ms! I don't expect anybody to believe what I just said until you actually see it because I would not have believed it two years ago when I first got involved with lip sync issues. I thought then that it could not possibly matter if you got within one frame (33 ms) since video is simply a lot of still frames visible for 33 ms each. What I have come to realize is that what our brains "see" when watching speech is a few hundred ms sample of lip movement not individual frames. For the same reasons our visual persistence allows TV and movies to work blending these individual snapshots into our perception of a continuously moving image, our brains "see" the lip movement pattern similarly as a continuous movement or undulating waveform. When the sound we hear does not "fit" that waveform we notice it. That is if the sound does not have appropriately placed peaks and valleys in sync with that image our brains can detect it (from my experiments even down to a single ms). If the sound is delayed a little past the image as it always is in nature our brains can interpret it as being away from us but if the sound occurs “early” (as it does when video is delayed) our brains can not process what's happening (since from its experience that is not a possibility).

That’s the problem, now finally a REAL solution: Felston (www.Felston.com) of England has just released their DD540 Digital Audio Delay for the express purpose of correcting lip sync. It has a great IR Remote (with discrete IR commands for use with programmable macro remotes like the Pronto) which allows you to select one of two digital audio inputs (one optical and one coax) and apply a delay up to 680 ms in one ms increments. It features 6 presets per channel which allows you to quickly set the delays you need to correct your for various sources. Tweaking for perfect lip sync is a simple matter of pressing a + or - button on the remote. I have used Felston’s previous model, the DD340, since it first appeared and recently switched to the DD540 which adds a second digital channel, both coax and optical connections in and out, brightness control, more presets, discrete IR commands, etc. Both are great products but the DD540 is the one to get and it $229 it may turn out to be the best investment you will ever make to improve your home theater experience (if lip sync error is bothering you).

Note: If you also have analog sources you need to correct an A/D Converter can be used on one of the DD540’s inputs to give you both delay of analog and digital audio. Felston’s dealer for the US and Canada www.LipFix.com is offering a promotional bundle which includes the DD540 and an A/D converter for only $249 for a limited time. They bought 500 of the converters from a major manufacturer’s closeout and are offering it with the DD540 as a promotion which will end when the converters are gone. It’s a private labeled version of a converter that sells elsewhere for $40 to $75 so if you need to delay stereo analog signals too, that’s a great solution.

A comment on Av Amps that offer “lip sync” adjustment: All that I have examined imbed the adjustment as a single fixed overall delay which you must set in a hard to get to set-up menu where you can’t see the video and hear the sound. They clearly do not understand the Lip Sync problem. What they have done (one overall delay for you to set and forget) would work if the whole delay problem were caused by fixed delays in your equipment that applied to “all” inputs but that’s not true in most cases. It would come close if all you ever watched were DVD’s but even in that rare case adjusting for the small differences from one DVD to another would require a trial and error adjustment entering and exiting set-up until you got it right - but it should then be OK until you switch to a different DVD unlike the constantly changing lip sync offsets when watching broadcasts. Until Av Amp manufacturers “get it” and place dynamic adjustment of the audio delay on the main remote control (with + and - buttons like the DD540) you won’t be happy if you switch Av Amps to get lip sync correction. Your existing Av Amp and a DD540 is a much better solution.




Lip sync problems like this one can have a number of causes. The obvious ones are the amount of processing that video signals endure along the chain right through to the STB and MPEG compression delays, which vary according to the complexity and motion of the image displayed. Many digital processors, including DVD players and STBs, have an automatic and/or manual lip sync adjustment. Apparently, your Motorola 2500 doesn't, being, I take it, an older model. I don't know whether a firmware upgrade is available for it. It's worth a try. By the way, why aren't you using the component output from the digital STB? Assuming that your TV can accept it, it will improve your picture.

Ed

[edtyct]

Hey, Nick, interesting stuff. You mention your own experiments. Can you describe the design and method? Who sponsored them?

Ed

[toenail]

I just hooked up my Motorola DCT2500 digital cable box to the aux in on my Koss 4102 HTIB. Im using Composite Video In and Coax Digital Sound In ... Video is output Composite Video, Sound obviously goes through the 5.1 speakers.

When I try to watch anything on the TV from the cable box theres a LAG of about 1-2 seconds between the video and the audio....

WHY is this happening? is my cable box misconfigured? need a firmware update? need a newer box? my HT screwed up? ANYTHING???

Thanks

From what's stated above it sounds like you're running your composite video in and out of the HTIB receiver, then on to th TV. Try sending composite video directly from STB to TV without sending it through the HTIB receiver.