crystal - PFL and AFL

crystal supports up to five monitoring buses that can be used to configure PFL and AFL.

PFL (Pre-Fader Listen) can be used to listen to a source while its fader is closed (off-air). This allows you to check an incoming signal before opening the fader.
AFL (After-Fader Listen) can be used to listen to a source in isolation (at its mix level).

What is possible?

Up to five PFL/AFL buses can be configured (using the ON-AIR Designer). The number of available PFL/AFL buses is determined by the Power Core license. Usually, a single PFL bus is sufficient. If independent PFL outputs are required, or you need both PFL and AFL monitoring, then multiple buses can be defined. This is explained in more detail later. For now, it is useful to know that:

Each source can feed up to two monitoring buses simultaneously. For example, to feed both PFL and AFL.
On each fader strip, the PFL 1 bus can be swapped with another listen bus (from 2 to 5). This is useful if the surface has multiple operating stations, as you can configure independent PFL outputs from each set of faders.
The PFL mode defines how the surface keys operate: as PFL, AFL, or a combination. The PFL mode can be changed by an operator (from the Setup menu).
Each PFL/AFL bus can feed a dedicated speaker or be switched to the main monitoring automatically when a PFL (or AFL) is active.

The rest of this topic describes how PFL is defined in the standard configuration. The operation may vary if the configuration is customized.

Operation

In the standard configuration, PFL can be selected by pressing MF Key 4 (on the source's fader strip) or pulling back on a fader (to activate the overpress).

All sources feed a single PFL bus (PFL 1) and the default mode is "PFL SUM". This means that:

Multiple PFLs can be selected.
Where faders are closed, sources are summed onto the PFL bus.
When a fader opens, PFL is cancelled.
Where faders are open, sources are put into "PFL prepare". In this instance, nothing happens until the fader is closed. Once the fader is closed, PFL becomes active.

The PFL key has three possible states. The colors used can be modified by the ON-AIR Designer. The following colors are used in the standard configuration:

Dim white = PFL off.
Full green = PFL on and fader closed (PFL active).
Dim green = PFL on and fader open (PFL prepare).

In the example below, the source Mic 02 is in "PFL active", while Codec 1 is in "PFL prepare".

Fader Overpress / Backstop PFL

The fader overpress can be enabled or disabled from the Setup menu. When enabled, the operation is momentary:

Pull back on a fader to activate PFL.
Release the fader to cancel PFL.

PFL Monitoring

In the standard configuration, the PFL output is switched automatically to the headphones (HP) whenever a PFL is active. The previous monitor source is re-instated once all active PFLs are cleared. If PFL is selected (as a Contol Room monitor source), then PFL is switched to both outputs: HP and CR.

If Split is active, then you will hear different signals in the left and right ears of the headphones: left = the selected monitor source (in mono); right = the PFL bus (in mono). You can use this to keep listening to a monitor source (e.g. PGM 1) while cueing up another source.

The Mon PFL output can be connected to a separate PFL speaker, either by editing the default audio connections (using ON-AIR Designer) or by making a connection from the 'Routing' page (on the GUI).

You can use the PFL controls (at the top of the Main module) to check that signal is present and Clear all active PFLs.

PFL Modes

The PFL mode defines how the surface keys operate: as PFL, AFL, or a combination.

The default PFL mode is "SUM", but this can be changed by editing the configuration (using the ON-AIR Designer). The PFL mode can also be changed by an operator (from the Setup menu).

The table below describes all possible options.

1	SUM (default) Multiple PFLs can be selected. Where faders are closed, sources are summed onto the PFL bus. When a fader opens, PFL is canceled. Where faders are open, sources are put into "PFL Prepare". In this instance, nothing happens until the fader is closed. Once the fader is closed, PFL becomes active.
2	SUM R Known as SUM Recurring. Identical to SUM mode, but PFL recurs if you open and then close the fader. In this mode, you must turn off PFL by deselecting the PFL key.
3	PFL Identical to SUM mode, but the PFL keys inter-cancel. This means that only one source can ever be in "PFL Active" or "PFL Prepare".
4	PFL R Known as PFL Recurring. Identical to PFL mode, but PFL recurs if you open and then close the fader. In this mode, you must turn off PFL by deselecting the PFL key.
5	PFL A Known as PFL Always. Identical to SUM mode, except that sources are always put into "PFL Active" even if their faders are closed. i.e. there is no "PFL Prepare".
6	PFL AR Combines PFL Always and PFL Recurring. Sources are always put into "PFL Active", and PFL recurs if you open and then close the fader.
7	PFL PUSH Changes the operation of the PFL keys from latching to momentary. In this instance, you must press and hold a key to make PFL active. PFL cancels when you release the key.
8	PFL DJ A special mode for DJs that can be used to prepare a fader level before the source goes on-air. Start by pressing PFL to monitor the source and adjust the fader level. Then deselect PFL and press channel ON (to put the source on-air) - the fader jumps to the prepared level. Note that the prepared level is applied only once. So, if you take the fader off-air, and then press channel ON again, the fader jumps to 0dB as normal.
9	AFL Changes the operation of the PFL keys from pre-fader listen to after-fader listen. In this mode, multiple AFLs can be selected. AFL must be turned off by deselecting the AFL key.
10	AFL/PFL Combines AFL and PFL operation. The PFL keys operate as AFL when a fader is open and PFL when a fader is closed.