One of the problems in home theater is the issue of Audio Video Synchronization. What happens is that sometimes you may notice that the audio soundtrack is slightly ahead of the video image when watching a high definition cable/satellite program or upscaled DVD/Blu-ray Disc video on an HDTV. This is especially noticeable on close-up images of people speaking. It is almost as if you are watching a dubbed foreign movie.
The reason this occurs is that audio can be processed a lot faster than the video, especially high definition video. High definition video takes up a lot space and takes longer to process than even the new high definition audio formats or standard resolution video signals.
As a result, when you have an HDTV or home theater receiver that does a lot of video processing to the incoming signal (such as signals that are upscaled from standard resolution to 720p, 1080i, or 1080p), then the audio and video can become out of synch, with the audio arriving before the video.
The Solution: Audio Video Synch Correction Adjustment Tools
To solve this problem, there is a tool available in the operating menu on many newer HDTVs and home theater receivers, referred to as either "Audio Synch", "Audio Delay", or "Lip Synch".
Regardless of the terminology used, what these features all have in common are settings that "slow down" or delay the arrival of the audio signal so that image on the screen and audio soundtrack match. The settings offered usually range from 10ms to 100ms and sometimes up to 240 ms (milliseconds). Although this seems miniscule in terms of time, a 100ms change between the timing of the audio and video can be very noticeable.
Also, if you are using a home theater receiver that features audio processing via HDMI connection, you may have the option to set this function so that AV synch can be corrected automatically or manually. If you have a home theater or HDTV that provides this choice, try both options and see which one gives you the most consistent correction result.
Check out a photo example of an AV Synch Tool that may be found on a Home Theater Receiver (copyright Onkyo USA).