Patent US 4,839,733

A method and system for synchronizing a digital signal of an audio message at higher quality with another signal of the same audio message at lower quality. The invention synchronizes an auxiliary high quality audio digital sound signal source with the ordinary quality analog sound signal coming from a conventional analog sound track on motion picture film as the motion picture is being shown and maintains effective synchronization in spite of missing segments of the sound track due to film splices. The invention does not require synchronization tracks, markers, codes, time codes or other extrinsic data. The only requirement is that the higher qualtiy audio message recording, e.g. in a digital medium, be made from the same "master recording" (or a high quality duplicate thereof) as the sound track so that the auxiliary recording have the same informational content as the sound track. In order to maintain synchronization of the high quality audio message in spite of missing segments of the lower quality audio message, the higher quality message is caused to precede the lower quality message, and is temporarily stored in time-delay means, such as a FIFO overwriting memory store. Correlation is achieved by re-iterative subtractions between digital numbers representative of characteristics of the absolute value envelope of the ordinary quality message signal and digital numbers representative of characteristics of the absolute value envelope of the high quality message. When the missing segments of the cinema sound track amount to more than the time-delay storage capability of the time-delay means, the system immediately smoothly "fades" over to utilize the conventional analog sound track of the cinema film for uninterrupted sound accompanying the motion picture being viewed by the theater audience. Re-synchronism is quickly achieved, and the system immediately automatically smoothly "fades" back to the higher quality sound.