Pops, clicks and distortion on the fiber optic I/O may be caused by Word Clock discrepancies. Word Clock problems arise when the digital frame rates of two devices are not aligned. In order for two or more digital devices to be properly aligned only one device can be set as master. Word Clock allows other deices to be synced or 'chained' to this device. In other words, the 'chained' devices are set as slaves. (Similar to a MIDI daisy-chain). The BNC connectors allow one unit to be slaved to another unit, which is one way to sync two or more digital devices. Another way to sync digital Word Clock devices is through the Word Clock signal that is carried either by the S/PDIF I/O or the ADAT I/O.