The ACO-4400 is a 1RU automatic changeover system which, when combined with both the Primary and Backup SRG-4400 units, provides a fully redundant and fault tolerant master reference system. Up to 12 signal types can be fed from a pair of SRG-4400 reference generators, and the ACO-4400 handles automatic failover / changeover function based on any single signal failure, creating a fully fault tolerant system. To allow for mixed format requirements and offer maximum flexibility, each channel can be set to measure analog color black, 3G/ HD/ SD SDI video, or AES/EBU audio (75 Ohm). Each channel has a Primary input, a Backup input, a Common output and a relay that switches one of the inputs to the Common output. All channels measure both the “primary and “backup” signals. The ACO-4400 ships standard with dual “hot swappable” power supplies which are directly accessible from the front panel.