The above schematic shows one method of interfacing to the Denon DN-720 Cassette Desk to allow its use as an air-check machine. When the toggle switch is in the open position the deck functions normally from the the front panel controls. When the switch is closed the deck wil alternate between Play (Record) and Pause depending on the condition of the studio muting relay. The toggle switch is labeled "Normal" in the open position and is labeled "Skim" in the closed position. The studio muting relay used could be one set of contacts on a Henry SuperRelay.