The PL 2404 provides two options for soloing input signals in headphones connected to the front panel headphone jack—Pre Fade Listen (PFL) and After-Fade Listen (AFL). The PFL/AFL switch in the main section allows you to choose between these two modes of operation. Although they may at first glance appear similar (and both are non-mix-destructive), there are in fact several significant differences between the two.
The main function of PFL is to allow you to check that a signal is actually arriving at a particular input. When the PL 2404 is in PFL mode and a channel Solo switch is pressed in, the pre-fader (but post-EQ) signal of that channel alone is routed to the headphone output if the Solo/Main switch is up (set to Solo mode).* The Bus outputs, Main outputs, and Control Room outputs are not interrupted during a PFL solo, so you can press any channel Solo switch even during recording or live performance without affecting the main signal flow. This also makes it possible for you to correctly cue up a tape or CD before bringing it into the main mix.
The main drawback to using PFL mode, however, is that it does not allow you to hear a signal in context. For one thing, because the PFL soloed signal is monitored pre-fader, it may sound considerably louder or softer than it actually is in the main mix (depending upon the current position of the channel Level control and, for channels 1 - 3, the mic Trim control). Also, the Balance control has no effect during a PFL solo—if the soloed channel has both its odd- and even- numbered inputs connected, you’ll hear both inputs, panned hard left and right; if only the odd-numbered input is connected, you’ll hear the signal monophonically.
Therefore, you may in some circumstances prefer to use AFL mode, which provides in-context soloing. When the PL 2404 is in AFL mode and a channel Solo switch is pressed in, the post-fader, post-EQ signal of that channel alone is routed to the headphone output if the Solo/Main switch is up (set to Solo mode).* Like PFL, AFL is non-destructive to your mix—the Bus outputs, Main outputs, and Control Room outputs are not interrupted during an AFL solo. However, over the headphones, you’ll hear the AFL soloed signal at its current level and in its current pan position (if only the odd-numbered input is connected) or with the correct relative levels of its two inputs as set by the Balance control (if both the odd- and even-numbered inputs are connected). By pressing the Solo/Main switch during an AFL solo, you can quickly compare the soloed signal on its own with its impact on the overall mix.
In both PFL and AFL modes, you’ll hear the soloed channel with its EQ settings and (if the soloed channel is one of channels 1 - 4) all effects being applied and returned via the channel insert. Note that there is no provision for soloing signal arriving via the PL2404 Aux returns.
LEDs in the meter section allow you to see at a glance which mode the PL 2404 is in. The leftmost LED (labeled “PFL”) lights steadily green when the mixer is in PFL mode, while the center LED (labeled “AFL”) lights steadily red when the mixer is in AFL mode.
*If the Solo/Main switch is pressed in (Main mode), connected headphones will always receive the complete Main mix (including signal from the Aux Returns) whether or not any channel Solo switches are pressed in.
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