An insert cable is a type of Y-shaped audio cable that has a 1/4" TRS (tip-ring-sleeve) connector at one end , and two 1/4" TS (tip-sleeve) connectors on the two other ends. The tip of the TRS connector is wired to the tip of one of the Y-ends, and the ring of the TRS connector to the tip of the other TS connector. The sleeve of all three connectors is tied together. Alternatively, if the outboard gear uses XLRs, see Making a custom insert Cable.pdf. Insert cables are used to place a piece of signal processing equipment, such as a compressor, in-line with a channel on a sound console (literally, one "inserts" the gear into the channel). From this thread: http://www.controlbooth.com/forums/sound/252-inserts.html Consoles using the above scheme are known referred to as having "single-point inserts." More expensive desks use XLRs for ins and outs, allowing for a balanced signal throughout the chain.