Alesis Studio 12R Reference Manual page 19

Note that you will not hear any signal through the Studio 12R if the
INSERT jack is plugged in and the signal is interrupted in that loop (by the
other cables being disconnected, the processor being turned off, or the volume turned off in
the processor).
Connecting an in-line processor
1. Obtain a "stereo splitter" insert cable from your dealer.
2. Connect the stereo (TRS) end to the INSERT jack of the Studio
12R.
3. Connect the mono plug from the tip connector to the input of
the processor.
4. Connect the mono plug from the ring connector to the output of
the processor.
If you're not sure which mono plug is from the tip and which is from the ring, check to see
if the cable is labeled. If not, simply try it one way and if the signal doesn't pass through,
swap the input and output plugs the other way.
The [INSERT] jack may also be used as a direct output to a
multitrack recorder such as the ADAT. The send from the insert
jack is where the cleanest mic preamp signal may be obtained,
without passing through the EQ or channel circuitry. Simply insert
the plug to the first "click" (the ring connector) and it will not
interrupt the flow through the mixer, while providing a direct
output. Or, put the recorder into INPUT mode and insert the plug
all the way, connecting the input and output of each track of the
Studio 12R Reference manual
Insert Points
Send
Return
Ground
Tip
Ring
Tip
Ring
Sleeve
Sleeve
Connections
18