HDTV sound / video sync issues?

Discussion in 'General Electronics Chat' started by spinnaker, Dec 3, 2011.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    I just purchased my first HDTV. I was disappointed to see that in some cases the video is not synced with the sound. Most noticeable is when there is a close up of someone speaking.

    So I did some searching and found that this is a fairly common problem with HDTV.

    Why have I never noticed this on analog? Why can't it be fixed? I would think some kind of sync pulse could be broadcast with a delay configurable at the TV.

    BTW I still have an old non HD Tivo. I run 2 sets at the same time. One upstairs one down. That way I can go between floors and watch the same program. If I stand where I can hear both sets, it is kind of strange. I can hear what sounds like an echo so I am guessing one of the sets is delayed a bit. I never noticed this when I had two analog sets.
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    TV producers do not care about whether the sound is sync'd with the video.
    They don't even care if speech can be understood normally because they usually cut all the high audio frequencies.

    Did you notice that the sound/video sync and normal high audio frequencies are excellent in commercials?
     
  3. spinnaker

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    Oct 29, 2009
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    What is the purpose of cutting the high audio frequencies?

    I always thought it was my poor hearing. It sounds like a lot of actors mumble to me. Until a friend and I watched the same show separately on different sets with DVRs an actor said a line and it could not be understood. We both have DVRs and both happened to replay the line a number of times. It just could not be understood.

    I understand that the commercials are not louder just the frequencies are manipulated (mixed differently I guess) than the television show to make them sound louder.
     
  4. Audioguru

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    Dec 20, 2007
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    Many people wrongly believe that speech has a frequency response up to only 3khz. But that is only for the vowels. The consonants (s, t, p, f, sh, th and many others) are important for understanding speech and are high frequencies up to 14kHz.
    Have you heard only vowels from an underwater throat microphone? It is only grunts and groans.

    Maybe TV producers are deaf to high audio frequencies so they cut them. Then they also cut the important consonants.

    Lately TV producers compress the heck out of audio. Background sounds blast at full volume until there is music or speech. The attack time of the compressor is slow so the first syllable of every spoken word blasts at full volume then the remainder of the word is at normal volume. Each word sounds like a hammer.

    With excessive compression then high frequencies are cut even more because the level of the loud vowels control the amount of compression.

    TV announcers wear their lavalier mic hidden down on their chest (frequently beneath the desktop) where it picks up strong low frequency sounds through the body which activates the compressor but it muffles the weaker distant high frequencies from the mouth.

    Actors rehearse their act over and over until it is memorized. Then their speech is automatic and they don't know they are mumbling. Simply read the lips (on the actors who are not even talking!).
     
  5. crutschow

    Expert

    Mar 14, 2008
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    The delay is caused by the time it takes to process the video waveform, which can be significant for digital TV, enough to cause a noticeable difference between the video and audio. Most modern home audio-video receivers have an adjustable audio delay so you can sync the audio with the video. Perhaps the TV you purchased does not have the correct audio delay built-in to match the video processing delay. Who makes it?

    You never had that with analog TV since there is little picture and audio processing being performed and thus they are both presented virtually instantly as they are received.
     
  6. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    Thanks for the answer.

    Vizio is the manufacturer. I will look at the setup again to see if there is a delay.

    But I don't know if a set delay would work since it only occurs on some stations.


    I need to contact Vizio on another matter, I might mention the sound issue.
     
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