Why do Plasma tv's have sound delay problems?

d123456

Standard Member
A friend of mine has this Hitachi plasma and now it seems the new Panasonic range (70) suffers from the same problem.

What the hell? the easiest thing for a tv is to route the audio through to some kind of audio out. Why does this happen?
Why why why?
And it IS very annoying, you get the lip sync problem on the Hitachi it is so notable the movie becomes unwatchable. Steer away from Hitachi plasma's.
It goes for all inputs (component, hdmi, scart, etc!)
 

interbear

Well-known Member
A friend of mine has this Hitachi plasma and now it seems the new Panasonic range (70) suffers from the same problem.

What the hell? the easiest thing for a tv is to route the audio through to some kind of audio out. Why does this happen?
Why why why?
And it IS very annoying, you get the lip sync problem on the Hitachi it is so notable the movie becomes unwatchable. Steer away from Hitachi plasma's.
It goes for all inputs (component, hdmi, scart, etc!)


I have a new Panasonic PX70 - no sound delay problems at all, I'm using both SCART (DVD) and HDMI (Sky) inputs.
 

Black Adder

Active Member
A friend of mine has this Hitachi plasma and now it seems the new Panasonic range (70) suffers from the same problem.

What the hell? the easiest thing for a tv is to route the audio through to some kind of audio out. Why does this happen?
Why why why?
And it IS very annoying, you get the lip sync problem on the Hitachi it is so notable the movie becomes unwatchable. Steer away from Hitachi plasma's.
It goes for all inputs (component, hdmi, scart, etc!)

The reason is quite simple. You'll kick yourself for not realizing before:

Due to the size of plasmas (being quite large), there is a tendency for people to sit slightly further away from the screen.

This causes light/sound delay due to the very different speeds of light & sound. The light from your plasma is travelling at 186,000 miles per second to your eye, whilst the sound is hugely retarded due to sounds crawling speed (compared to light).

This obviously causes the lip synch to be out quite considerably. Notice for instance that the speech delay is ALWAYS behind, never in front.

If it were the other way around, this would cause a major re-think of current quantum theory.

Hope this helps......:D
 

choddo2006

Distinguished Member
hmm

er

sound at 600 miles an hour = 268metres per second
So it takes the sound roughly 0.01s to cover 5 meters, about as far as most people sit from a TV. I don't think anyone human would notice a 0.01second sound delay, it's about half of a single frame of video so how would you even tell?

In actual fact, lipsync problems on large digital TVs is actually the complete opposite. The speech is always in front, not behind the video which is the opposite of what your brain naturally expects from real life experience of seeing & hearing distant events which is how it's so jarring.

And the reason it's ahead is that it takes time for the TV to process most video signals but audio gets piped straight through.

This is why most good amps and video processors have an audio DELAY function. I think the SkyHD box has one too iirc.
 

scotty38

Active Member
The reason is quite simple. You'll kick yourself for not realizing before:

Due to the size of plasmas (being quite large), there is a tendency for people to sit slightly further away from the screen.

This causes light/sound delay due to the very different speeds of light & sound. The light from your plasma is travelling at 186,000 miles per second to your eye, whilst the sound is hugely retarded due to sounds crawling speed (compared to light).

This obviously causes the lip synch to be out quite considerably. Notice for instance that the speech delay is ALWAYS behind, never in front.

If it were the other way around, this would cause a major re-think of current quantum theory.

Hope this helps......:D

You are sort of correct, the actual reason is because typically your eyes are closer to the screen than your ears.

Try this simple test - turn around so that the back of your head is facing the screen, now your ears are closer and notice how the delay has disappeared.....

:D
 

xit2050

Well-known Member
Great thread... keep 'm coming.

:rotfl: :rotfl: :rotfl:
 

SimonTSM

Member
It used to be a problem with low-end plasmas. I thought it was all sorted.

It basically boils down to the fact the image has to be processed in some way by the use of DSP. Quite advanced FFT and convolution processing is made to scale, remove artifacts and noise for example. Slow or poor DSP will take time to process the image, giving a delay to the image.

A few ways to solve delay:
  • Buy a higher quality plasma that has very good processing.
  • Buy an audio delay, or use one in a audio processor.
  • Buy a 100,000,000 inch screen and place it in geostatic orbit around the earth. The time delay from the radio signal going to the screen and the light coming back may just be enough to correct lip sync.
 

chubblies

Standard Member
I noticed this also when my panny px60 arrived, it was fine on component out from the sky/xbox/whatever through my hifi, but slight delay through the tv speakers, if you had both turned up at the same time the tv would always be a fraction of a second behind the hifi.
The only reason I can think of is the virtual surround sound processing side delaying slightly whilst it messes with it, but mine still delays slightly with all that disabled.
As for the speed of sound theory:rotfl:
 

Bumtious

Banned
The way to solve this is quite simple.

I watch 1 set in the front room and use the sound from the back room.

I get perfect Sync :cool: :rotfl: :rolleyes: :laugh:
 

SimonBalaam

Standard Member
You are sort of correct, the actual reason is because typically your eyes are closer to the screen than your ears.

Try this simple test - turn around so that the back of your head is facing the screen, now your ears are closer and notice how the delay has disappeared.....

:D


So would you suggest buying a mirror to put on the opposite wall of the TV to solve this problem??:rolleyes:

Or would that make the problem worse and i get the opposite effect?:oops:
 

aktiv

Member
Just in case anyone was still actually interested in helping the poor OP out ;) , the problem is not specific to plasmas but can affect any type of display, including some fairly old CRTs, that happen to digitally process the incoming video signal. This became common in the mid 90s, initially on things like Loewe and high-end Sony models, but any decently designed display will be designed to take the known quantity of the internal video processing time and delay the audio to suit. This also applies to video sources; DVD players will delay the audio if outputting progressive instead of interlaced for example, as it inevitably takes a wee bit extra time to stitch together the interlaced frames. This time is measured when the product is being designed and any requirement to buffer the audio is factored in.

The problem arises with the scenario of splitting audio to a processor/amp and video to a display, a practice that has increased dramatically in last five years. As the audio processing side no longer 'knows' how long the video processing is taking, the likelihood of some lip sync issues creeping in increases dramatically.

As someone else has said, some processors have audio buffering to counteract this and this really is your best, and probably only, way round it. You can try and switch off some of the (probably unnecessary) video processing (noise reduction, 100Hz options etc.) to lessen any video delay, but this might only get you 1 or 2 msec and if you are noticing it the delay is probably >5 msec already. Poorer-quality displays will likely suffer more in this regard though. If your audio connections are analogue and your processor can take a digital signal, try that as the dac will usually induce a slight delay as well. Maybe a combination of the above will improve things to a point that it is no longer noticeable.
 

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