with color television this requires that the switching interval is coincident with the vertical interval in the television signal the switching control line therefore detects this particular interval and allows the switching in the digital cross point matrix to be coincident with that interval the description above covers the basic equipment used for a digital equipment assignment system the advantages of the digital assignment system over an analog system are that it increases the ability to multiplex channels without cross talk the same system may be used to switch audio signals using digital techniques and thus providing an audio video system which can pass through the same cross point the basis of the digital audio assignment system is similar to that of a digital video assignment system without the requirement of operating at a very high bandwidth it is therefore possible to interlace the audio signals with the video signals at the digital stage without substantially increasing the complexity of the equipment a basic audio assignment system will incorporate a precision analog to digital converter suitable for accepting audio signals the digital data from the analog to digital converter will then be applied to the parallel to serial converter at a time when it is not accepting data from the video equipment for television applications a suitable period would be that known as the back porch front porch or sync pulse the period required to transmit the audio signal is very short compared with that required to transmit.