PFL - Pre Fade Listen.
PFL is a function of many audio devices but is generally recognized as a function of a Mixing Desk.
What does it do?
PFL is a way of monitoring a signal in an audio chain. As the name suggests it is taken BEFORE (PRE) the channel fader (or other type of volume control). PFL is usually activated via a button on the Channel Strip. A PFL signal is usually sent to the Headphones output on a device which overrides the normal signal. It also monitors on channel meters (sometimes PFL may have its own meter in the master section).
The PFL signal you hear and see is independent of the channel fader, grouping and (apart from very rare cases) the channel mute/on switch.
What is it used for?
PFL is used to monitor a signal without the need for the channel fader to be up (channel live). It is also used to solo a particular instrument to check for any problems or to fine tune during the show, without affecting the shows sound. On certain mixing consoles a wedge type monitor speaker can be plugged in to use as a monitoring device (for PFL). This is handy when using a monitor desk as you can get a feel for what a musician on stage hears.
There is often a larger than normal light in the master section warning you that PFL is active. there is also usually a light on the channel strip alerting you to which channel has PFL active. Sometimes this light is combined with the PEAK/CLIP led on the channel, its important to know which is functioning at the time. On larger boards, digital in particular there may be a PFL cancel button which clears all PFL's. With a board with latching switches this is not possible.
It is often possible to PFL more than one channel at once.
- After Fade Listen (often called "Post Fade Listen")