Addressing Audio-Video Lip Sync at the Baseband Level
March 27, 2006
Part 4: Calibrating Ears and Eyes to Determine Lip Sync Errors You've got your test setup ready to evaluate any audio-video lip sync errors. See "Addressing Audio-Video Lip Sync at the Baseband Level, Part 3: Tools to Help the Process." But before you go out to the racks, spend some time on the test bench training yourself to detect lip sync errors, and provide the proper correction. As a wise person once said, "test the test equipment first." A spare frame synchronizer, with built-in audio delay (where the delay can be manually adjusted) is a good piece of gear to purposely create different amounts of audio-video lip sync errors to help "calibrate" your ears and eyes. Using your source material, adjust the audio delay from an out-of-sync condition until you just detect the audio becoming in sync with the video. Note the delay setting. Keep adjusting until you see audio and video out of sync again. Note the delay setting again. Now you have some idea of the range of audio delay where audio appears to be in sync with the video. A good final "eyeball" setting would be somewhere in the middle. As you gain more experience you may find that you are better able to detect the out of sync thresholds.
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