Clean up your mixes with high-pass filters

Even if you don’t know much of anything about EQ, compressors, bussing, or whatever, one of the best and easiest things you can do to clean up your mixes is with a high-pass filter.

Different from other EQ controls, high-pass filters (also known as a low-cut) do not boost signal level. All they do is severely attenuate sounds below a certain frequency point (thereby allowing the higher frequencies to pass through). The screenshot below shows the left side of the EQ window with a high-pass activated. The controls on the far left, labeled “HPF,” allow you to select the frequency point at which attenuation kicks in (called the cutoff frequency, and is actually 3dB below unity) as well as how steeply the attenuation occurs. Slope is measured in dB/oct, so a higher number indicates a more rapid attenuation as you go down the frequency spectrum.

So how does this magically help your mixes? Except for low frequency-heavy sources such as bass guitar, kick drum, etc, there’s nothing useful or musical down there. But there is noise—low-end rumble from stage leakage (drums, guitar amps, footsteps, other musicians), HVAC, etc. All of this garbage, even if low-level, gets added to your mix, meaning your PA speakers have to reproduce that along with the good stuff. They can do a cleaner job without it, so get rid of it everywhere. Put a high-pass filter on all your channels except bass, kick, maybe piano (I’ll come back to this in just a bit…).

If you are a newbie (it’s okay, just admit it and get to work) just turn them on and set to 80Hz. But when you have some time to experiment, run some tracks through the console and, one at a time, adjust the frequency select on the filter. Slowly turn it higher until you begin to hear the low end of the sound start to go away. You don’t want to lose the body of the sound, so dial it back a tad and you’re set. Sometimes we dial it higher for vocals in order to reduce plosives, though it won’t work entirely because those sounds aren’t just low frequencies.

Getting back to the low frequency instruments, you can put filters on bass guitar, kick, and piano. Dial the frequency select up just enough to eliminate very low-end rumble and boominess. Depending on your PA system and room acoustics, these low frequencies (say below 50ish) might get too boomy. So just roll those off, which still leaves the main body and fullness of the instruments.

This trick also works great for studio mixing, so use them the same way, though maybe not set quite as high. As always, use your ears.