Solid State Logic SSL 18 User Manual page 21

When TALK is engaged, the monitors will automatically dim to the level set in the Monitoring section as shown below.
7. GAIN, +48V & LINE
This allows +48V Phantom Power to be switched in to power the Talkback Mic, or switch to LINE Input for a pre-amplified Talkback Mic
signal. 3 fixed Mic Gain settings are available - 30/40/50 dB.
8. LMC
The Listen Mic Compressor can be engaged on the Talkback Input Signal. This classic analogue compressor circuit was originally
used in the SL 4000 B console for communication purposes, to help hear what the musicians in the live room had to say before/after
recording takes. In use on the talkback input, it can be helpful to ensure the producer sat on the sofa at the back of the room can be
heard when the engineer is talking back to the artist who's recording. However, the 'heavily compressed' sound also works great for
creative uses e.g. connect a microphone set up in the live room as a 'smashed drum kit' room microphone, or, switch the talkback
input to LINE mode (TRS jack input), and re-process sterile DAW stems through the LMC circuit.
DIGITAL INPUTS
Up to 16 channels of ADAT Inputs and Outputs can be addressed by SSL 18, with the ADAT inputs showing up in the SSL 18 Mixer. 2
channels of S/PDIF I/O are also available, with the S/PDIF inputs also shown on their own input channel in the SSL 18 Mixer.
The Digital Inputs provide no gain controls. Gains should be set on the external device.
Routing to the Monitor Bus, HP A, HP B & LINE 3-4 is identical to the workflow of the Analogue Input Channels.
ADAT I/O at 44.1/48 kHz - 16 channels via the optical ports.
ADAT I/O at 88.2/96 kHz - 8 channels via the optical ports.
S/PDIF I/O at 44.1/48/88.2/96 kHz - 2 channels via optical port 2.
S/PDIF I/O at all sample rates - 2 channels via coaxial connections.
To use S/PDIF on Optical, you must select 'optical' in the SSL 18 settings menu.
PLAYBACK RETURNS
The 4x Stereo Playback Return channels allow separate stereo signals to be sent out of your DAW or other programs with assignable
audio outputs, into the SSL 18 Mixer as inputs.
Please note DAW Outputs 5-6 do not enter the SSL 18 Mixer, but can still be used as hardware outputs for external processing chains,
routing to them directly from your DAW or software program.