Method and apparatus for maintaining audio/ video synchronism in a television signal read-out from a digital buffer memory by a reference signal

Apparatus for maintaining audio/video synchronism in a television signal read out from a digital buffer memory in step with a reference signal, said television signals having an audio component and a video component, said apparatus including said buffer memory and means for converting said audio component and said video component respectively into a digital audio component and a digital video component and wherein said digital audio component has a word width in bits which is an integral multiple of the word width of said digital video component, and further comprising:

• means for deriving from said television signal, before its conversion by said converting means, a first video component sample rate clock signal, an audio component sample rate clock signal, a first compressed audio component sample rate clock signal and a first horizontal blanking signal, said video and audio components being respectively furnished to said means for converting said video and audio components into respective digital video and digital audio components;
• time-compressing memory means for said digital audio component having means for writing said digital audio component into said time-compressing memory means under control of said audio component sample rate clock signal and for reading said digital audio component in time compression out of said time-compressing memory means under control of said first compressed audio component sample rate clock signal;
• means controlled by said first video component sample rate clock signal for dividing the word width and multiplying the word rate of said compressed digital audio component respectively by an integral number factor;
• multiplexing means controlled by said first horizontal blanking signal and by said first video component sample-rate clock signal for inserting said time-compressed digital audio component of increased word rate in successive horizontal blanking intervals of said video component;
• means controlled by said first video component sample-rate for writing said digital video component and said inserted digital audio component into said buffer memory;
• means for deriving from a reference signal a second video component sample-rate clock signal, a second compressed audio component sample rate clock signal, an expanded audio component sample rate clock signal and a second horizontal blanking signal;
• read-out means controlled by said second video component sample-rate clock signal for reading said digital video component and said inserted digital audio component out of said buffer memory;
• demultiplexing means controlled by said second horizontal blanking means and having an input connected to the output of said read-out means for separating said digital video component from said inserted digital audio component read out from said buffer memory;
• means controlled by said second video component sample rate clock signal for multiplying the word width and dividing the word rate of said read-out digital audio component by said integral number factor to produce at an output a digital audio component having a word rate equal to said second compressed audio component sample rate;
• and
• time expanding memory means connected to said output of said word width multiplying means, having an input controlled by said second compressed audio component sample rate clock signal and an output controlled by said expanded audio component sample rate clock signal for producing a substantially continuous digital audio component at a read-out output of said time expanding memory means.