Have you ever sampled a great sounding kick drum from an old record or drum machine but realized there wasn't enough bass? If you're like me, you've spent countless hours trying to layer a modern sample under it, only to get all types of weird phasing, less headroom, and other problems that end up being worse than a lack of bass. You then reach for your favorite synth, and have another go at layering - flipping phase, nudging by samples, and generally just getting confused about what's "right" and what isn't.
Don't get me wrong, if you are really skilled, you can make either of these applications work. But it can be difficult and time consuming, especially when you really just want to continue making music.
So what's the solution to quick, fat, harmonic sub bass? A resonant high pass filter. Yep, you can add monstrous bass by removing bass. It sounds like it makes no sense, but hear me out.
When you're finding the sweet spot of the cutoff of your filter, you're tuning the cutoff frequency to the fundamental frequency of your kick.
Once you find that cutoff point, the resonance works to boost that frequency (and yes it totally adds distortion, which changes depending on how hot you're driving the input). The amount of resonance determines the amount of boost. The resonance can basically create an oscillator, or tone, which is why it sounds "stronger" than a traditional EQ, which would just boost frequencies that are not there to begin with.
Anytime you boost the fundamental frequency of a sound (the same way you would with an EQ), you're creating a "fatter" sound. Think about why a pure sine wave (which only contains the fundamental frequency) is so fat - it has not other frequencies eating up headroom, meaning it can be turned up loud without peaking the meters.
While this boost is happening, the high pass filter is cutting everything below that fundamental frequency, so you don't have to worry about those ultra low frequencies that people can't hear. You get more headroom this way and can turn that kick up louder !
If you're like me, you mix on smaller monitors. Unfortunately these don't project a lot of bass. If you're in a small room, a subwoofer is often going to cause more problems than solutions. When you use headphones you can make sure you're tuning the cutoff to the right frequency - this is hard to hear accurately on most speakers.
If you want to bang it out and really feel the bass, buy a Subpac ! The most helpful (and unpretentious) purchase I've made in the past two years. And no, I'm not an affiliate (maybe I should be?).
You may be wondering how to use this effect on something like a bassline, which often changes notes / frequency. Well, you may have already used this technique if you own a synth with "keyboard follow" parameter of its filter. Here, the cutoff frequency is tuned to each keyboard note you play. So engage a resonant hi pass filter, adjust the resonance and see what happens!
I'm not sure exactly where or when this application of HP filtering originated, but I first started using this technique DJing with Allen & Heath Xone mixers - I'd use the high pass filter while mixing, and instead of turning it off after, I'd just bring the cutoff all the way down and the whole DJ set would have enormous bass.
When done in an MPC, you can definitely hear how old skool hip hop and house producers used to sample disco / funk and turn those drums into hip hop drum samples. The MPC filters, especially the Z8 engine, are insane for this. But it'll work with an Octatrack or any sampler with a resonant high pass filter.
Remember to keep this a secret so you can be cool and have fatter kickdrums than everybody you know.