In this series, we’ll look at two things and talk about their differences. For the first installment, we’ll look at a common button on most audio consoles. The labels may vary, but the difference is important.
AFL/PFL—What’s the Difference?
AFL stands for After-Fade Listen while PFL stands for Pre-Fade Listen. Depending on the current state of your console, pressing solo in either mode may result in the same thing. Or it may be completely different.
Both AFL and PFL are solo modes. When you press the solo button on the channel, the output of that channel is routed to the solo bus and you hear it all by itself. We use solo for auditioning an input, checking for signal, and possibly setting EQ. We’ll get to this later.
On many consoles, you can also solo groups, VCAs and the master. So what’s the difference between AFL and PFL?
It’s All About the Pick-off Point
Pre-Fade Listen is just what it sounds like; the signal is picked off from the channel strip before the fader. Most of the time, it’s also pre-EQ, pre-dynamics and pre-Mute. You’ll have to read your manual to find out where the pick point is. Sometimes it’s after the HPF and LPF, but not always. Some digital consoles allow you to choose the PFL point, which is cool. Because PFL is pre-processing, it’s a great way to check the quality of the incoming signal before you do anything to it.
After-Fade Listen is a pick-off point after the fader. Typically, it’s also after EQ, dynamics and mute. So that means anything you’ve done to the signal with any of those processing blocks will be reflected in the solo output. In AFL mode, you will hear the effects of EQ, dynamics and filters. If the fader is off on a channel that you AFL, you won’t hear anything. It’s after the fader, remmember.
When To Use Them?
PFL is most useful for checking signal. When I line check a stage, I set the console to PFL and use the headphones to verify each input. Most of the time, the faders are all down (or turned off with VCAs), so nothing comes through the house. But I can hear it clearly with PFL. It’s also useful for verifying signal of a muted mic during a service. It’s not a bad idea to PFL your pastor’s mic a few minutes before he goes up to be sure you have signal. This has saved me many times.
AFL is useful for seeing if what you’re doing is helping or hurting the sound. If you’re trying to zero in on an offending frequency on an instrument, a quick AFL while you check the EQ can save you a lot of time. Many of my FOH friends and I generally prefer to EQ channels in the context of the mix—because it is a mix after all—but sometimes some isolation is helpful to solve a particular problem.
AFL is also useful to hear the blend of a group of instruments or vocals. I use it often on the BGV VCA to hear how my vocals are blending. Because the AFL happens after faders, I hear the blend based on the fader position. A quick AFL of the VCA can make short work of getting your vocals or drum mic’s blended.
Bonus: Solo In Place
This is known by a few other names, but what it does is the same. When SIP is pressed, instead of routing the PFL’d or AFL’d signal to the headphones or solo outputs, it routes it to the main L&R buss. That means everything but the solo’d channel is shut off and all you hear is that solo signal.
This can be useful or incredibly dangerous, depending on the situation. When you’re running a rehearsal, SIP can be helpful to identify a channel that might be lighting up a room resonance or something similar. But during a service, it can be devastating. It’s so dangerous that Digico requires you to press the SIP button for full two seconds just to engage it, and then it blinks red the entire time.
Don’t try out SIP during a service—ever! I rarely use SIP as I much prefer to EQ and alter dynamics within the context of the mix. But that’s what it does. Proceed with caution.