LG 57M - Manual (Page 21)

A18
Microphone Operation
On the left side there is a MIC (Microphone) jack. By plugging a
microphone in here, it may reduce the long length of cable needed to
reach the PC's sound card. In order to use this MIC jack, you need to
use the cable (supplied) to plug into the rear of the monitor (MIC
OUT) and into the MIC input jack of your sound card (if available).
If you lost the supplied cable, consult with your dealer or buy a stereo
cable.
Audio Features
A major feature of this monitor is its built-in audio system. This
conveniently integrates a stereo audio amplifier and speakers without
taking up any more space. Because the monitor is designed like this,
you can easily upgrade to audio capable multimedia applications by
attaching your PC with sound card to the back of this monitor. It will
result in significantly less cabling and space requirements.
Audio Connections
Use the supplied cable to attach to the rear of the monitor (AUDIO IN)
and to the sound card in your PC (line out). The cable will carry both
left and right channel signals in one wire. Make sure when you use
the PC to turn up the volume of the sound card all the way.