pre fader listening (audio) (PFL)
When mixing and crossfading audio and video signals, the signal can be tapped before or after the crossfade.
If it is tapped before the crossfade, it is called Pre Fader Listening (PFL); if it is tapped after the mix, it is called After Fader Listening( AFL).
With Pre Fader Listening, the audio signal can be tapped from the pre- fader bus and previewed with headphones before mixing. The volume of the pre-fader signal is independent of the main mix. Pre Fader Listening is normally used to check the level of the signal in the channel, to optimize the gain structure, or to confirm the presence of a signal before fading it up.