Refers to a connector known as a 9-pin D-Sub connector. It just so happens that Sony and many other companies have developed the majority of their synchronization protocols around this connector. Virtually every professional video machine has a 9-pin D-Sub connector for synchronization. Consequently the term 9-pin has become synonymous with the Sony synchronization standard (that is used by many other manufacturers). Actually there are many variations on the standard, but the phrase “Sony 9-pin” often gets applied to all of them without much regard for the specifics. The Alesis ADAT also uses the same type of 9-pin connector for its synchronization, but the protocol is different from and incompatible with any of the Sony standards.