Method and apparatus for maintaining audio/ video synchronism in a

Abstract

Both the analog and the video component of a television signal are converted to digital form, the audio component being converted at a much lower sample rate with a word length which is an integral multiple of the video word length. The digital audio component is then compressed by use of a temporary memory and read-out therefrom at a rate that is half of the sample rate of the digtal video component, after which the word length is halved and the word rate doubled in a shift register circuit. In that form the audio component is inserted in horizontal blanking intervals of the video component in a compatible form by a multiplexer, the output of which is read into a single picture field or full picture memory under control of an address generator clocked in synchronism with the incoming video component. The buffer memory is read-out at a rate controlled by a reference signal such as is used for synchronism in a television studio. On the output side the digital video and audio components of the television signal are separated by a demultiplexer, the audio word length is doubled and the word rate halved and the still compressed audio signal is expanded, to make available a substantially continuous digital component. The audio component can then be converted to analog form and will be correctly timed for accompanying the digital video component converted to analog form at the output of the demultiplexer. Separate audio signal delay circuits are thus avoided by the use of relatively simple multiplexing circuits and audio processing circuits.