Why Digital TV Images and Sounds Sometimes Don't Sync Q. I watch television through a small antenna attached to my HDTV. Sometimes the sound and picture get increasingly out of sync as a show goes on. The sound usually precedes the picture. Why does that happen? A. Although the pictures and sound in digital television are transmitted together (the technical term is "multiplexed"), they are "separate streams of data and are processed by separate hardware and/or software paths at television stations and in TV receivers," said V. Michael Bove Jr. of the Media Lab at the Massachusetts Institute of Technology. When the two streams do not match, "it might be the television station's or network's fault, or it might be your TV set's fault," Dr. Bove said. "The audio is supposed to stay synchronized to within a frame or two of video," he said, "but sometimes things are misconfigured somewhere at the origination end." Television receivers can also have hardware or software problems that cause loss of synchronization. "The easiest way to determine where the problem lies is to watch the same program on another set at the same time and compare the audio lip-sync," Dr. Bove said. Questions of general interest will be answered in this column, but requests for medical advice cannot be honored and unpublished letters cannot be answered individually.