Updated: Jun 7, 2019
Thanks for checking out the One Simple Thing blog. For this week we’ll go over an easy tool that a lot of audio devices are equipped with but we may not all be taking advantage of.
What is a high pass filter? A high pass (or low cut) filter does what the title implies; it lets the high frequencies pass through while cutting out the low frequencies. Some devices use a fixed frequency (usually around 80hz) while others give you a frequency range to choose from (usually around 200hz and lower). They are not solid wall filters, and will cut off from the given frequency at anywhere from 3db to 18db or so per octave. Again, some devices will give you a choice and some will have a fixed slope.
Why is it good to use? Most of the sound we are producing doesn’t go down into the 60hz range, and even if it does, the microphone, processor, and/or speaker we’re using does not. And even if those things do produce extremely low frequencies, are they sources that we want to go that low? Using a high pass can give more clarity to speech, vocals, and instruments while removing noise to make sources that do use those frequencies (i.e. kick drum, keyboards) come through clearer. Remember, your sound sources are competing for the frequencies your speaker can reproduce, so removing competing frequencies where you can is an easy help.
It’s good to know your high pass filter as well because maybe it has been engaged on your device and you didn’t know it. Kick drum or synths not sounding as boomy as they should, or different than they have in the past? Check to see if a high pass is engaged. That may be your solution.
So, when are good scenarios to use a high pass? My default is to have them on and turn them off for certain sources. I know that for kick drum and prerecorded sources I know I won’t want the high pass engaged, but beyond that on is the default. For bass guitars, synths, and a few other instruments, I will engage on a case by case basis to see what works best with the equipment and situation. For things like vocals and guitars, I know that I will want the high pass on.
The high pass can also be used for install situations. Most processors will have a high pass available per channel or on the master output. Per channel is great, but it will work on the master out as well, especially if you’re working with ceiling and/or pendant speakers (I know ceiling subs exist, but I’ve yet to hear a good one. Feel free to prove me wrong at InfoComm).
Use the high pass to help give you a quick and easy removal of unwanted frequencies. This will help give you a clearer mix with just a little effort. Did I miss a use? Let me know!