The solo button is a useful feature found on most any console; analog, digital and virtual. What the solo button basically does is it lets you listen to just the soloed track. There are a handful of variations of how the solo may work, but at it’s simplest, it soft mutes all the rest of the tracks and only allows the selected track to be heard.
What was just described above is called solo-in-place. “It soft mutes all the rest of the tracks and only allows the selected track to be heard.” With solo-in-place the same output is used for solo as for playing the rest of the tracks. This is what most DAWs default to with their solo function. Many have an “S” like seen here, many are yellow and some even have icons (like little headphones in Garage Band).
PFL and AFL
Pre-Fader Listen and After-Fader Listen (PFL and AFL) work a little differently than solo-in-place and is more commonly found on analog and digital consoles and in advanced DAW features. Both of these give you the opportunity to listen to your soloed information through a different output. For example you can solo a track during a live performance having just that track sent to the headphones while not altering the main mix going to the audience. The difference between PFL and AFL is where the signal is sent from, pre-fader or after-fader. This could be useful if you want to hear a signal before it is attenuated (turned down) by the fader for instance.
Many DAWs have a solo safe feature. This is useful to do to auxiliary returns for reverb and delay. Solo safe will keep the track from being soft muted when another track is soloed. Let’s say you are soloing a vocal track. The vocal is being sent to a reverb through an auxiliary send and return. If you solo just the vocal track, you won’t hear the reverb. But if you are soloing it to hear how it sounds with the reverb. Now you have to also solo the reverb return track. If the return is solo safed then the reverb for the vocal track will still be audible when just the vocal track is soloed.
The solo button is an excellent tool that can help you momentarily focus on specific elements of a mix. Make sure to avoid the common pitfall of soloing everything. This can cause a headache as your track count increases and you want to audition a single track. Enjoy the solo button. Use your new found information to let it work for you.