Audio Signals Out Of Sync With DTV

The Advanced Television Systems Committee (ATSC) has convened a subgroup to work on the growing synchronization problems between audio and video signals during digital television (DTV) broadcasts and receiver processing. Latency generated by the new DTV infrastructure has yet to be worked out. Delays have been estimated at anywhere from ""a matter of milliseconds"" to ""several seconds,"" with the audio proceeding as well as trailing the video. Home viewers will notice the problem if audio lags video by as little as 30 to 68 milliseconds (a frame is 34 milliseconds), and even be detected if the audio is as little as 17 milliseconds too early, depending upon whom you talk to. The ""growing latency pain"" varies from receiver to receiver and can get worse as a feed progresses.Blame both receiver manufacturers and broadcasters who are operating with no analysis tool to verify that time stamps are correctly being applied. Further, some sources claim that certain timing reference aspects of the MPEG standard were not well defined, and there is no set reference points for audio/video streams to comply with time stamps. Without timing reference points, decoders could make untrue assumptions about incoming streams and cause latency. The problem is also evident often on DVD as well.Industry sources say that the problems are not insolvable but just ""growing pains.""