In-Line Processing Using The Insert Jacks (Compressors & Equalizers) - Alesis MULTIMIX 12R Reference Manual

Connections
You don't need to connect anything to the other input of the effect,
because most effect units use the stereo inputs only to provide a path
for the "dry" stereo signal when the effect is connected directly
between an instrument and an amplifier. In mixing applications such
as with the Multimix 12R, you will set the effect's wet/dry balance all
the way to "wet" (effects only, no direct signal). The effect device will
generate an artificial stereo output from the signal input. Check the
manual for your effect device for more information.
On the other hand, true dual-channel effects processors (such as the
Alesis QuadraVerb 2) may be connected to two different sends to take
advantage of the dual processing capability. Dual-channel processors
allow the left and right inputs to be used for different kinds of effects
(for example, the left input to a stereo chorus while the right input is
used for a stereo reverb).
Using Aux 1 as an effects send
Note that [AUX 1] may also be used as an extra effects send. Although
Aux 1 is a pre-fader send, and normally used for stage monitoring or a
separate headphone mix while recording, it may also be used as an
effects send so you can add different effects to different channels. Just
remember that the "PRE" under [AUX 1] means that when you move
a fader up or down you won't change the level going to an effect from
Aux 1. If you change fader levels, you will need to adjust Aux 1 levels
to maintain the same balance between dry and effected signal.
In-line processing using the INSERT jacks
(compressors & equalizers)
Some signal processors are designed to be used on one signal at a
time, with the entire signal being processed instead of a mix of effected
and uneffected signal. The purpose of the INSERT jacks on channels 1-
8 is to allow you to insert a compressor, equalizer, or other effect into
the signal path of a single channel after its preamplifier and [TRIM]
control, but before the Multimix 12R's own EQ, aux sends, and fader.
The INSERT jacks may also be used as direct outputs to a recorder.
The INSERT connector is a TRS (tip/ring/sleeve) 1/4" jack which
consists of an insert send (the tip of the TRS plug) and an insert return
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