SoundCraft B400 - Manual (Page 44)

4.16 B400 Functional Description
PPKK
The PK LED monitors pre-insert and post-fade signal levels. If either of these
points rises to 6dB below clipping the LED will illuminate.
SSPP ((SSiiggnnaall PPrreesseenntt))
The signal present circuit monitors the output of the mix amp. The SP LED illumi-
nates when a signal is present on the Group Mix bus.