insert cable

[mbenonis]

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

... I just wanted to add a bit more in that an Insert uses a special cable called an insert cable. Its a TRS or Tip Ring Sleeve 1/4" plug that splits the signal to a "Send and Receive" to two TS or Tip Sleeve 1/4" plugs. Basically it will look like a Y cable--one TRS to two other cables that are TS, however it is not a Y cable and is sold under the title Insert Cable. On these cables, the Tip is usually being SEND of the signal out of that channel, and the Ring (the little part between the tip and the sleeve) being the return of the signal back into the channel. ...

ASCII drawing:

/_\ <-TIP (SEND)
|_| <-Ring (RETURN)
| |
| | <-Sleeve (GROUND/COMMON)
|_|
| |

A TS Cable is the same 1/4" jack as above excpt there is no center ring band at the end.

As Cruiser said--this allows you to "insert" an effect, compressor/gate or EQ onto that channel alone to effect that channels sound alone. The Insert breaks the signal path in the console--routes that signal to whatever you want, and returns it back in the chain right where it broke it. Inserts can be on channels, but they can also have inserts on the Mains Outputs--which allows you to insert a limiter or compressor on the entire mix, or you may have inserts on Auxillary outputs to do the same. Inserts are usually very common on most sound consoles, they are fun to use and very useful for certain things if you have the outboard gear and the time & need to use them.

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.