Pair a boost and a cut, part II: low frequencies

In yesterday’s post, we talked about how to make a relatively dramatic high-frequency bell-shaped boost, and then to pair it with a high-frequency cut in the form of a lowpass filter, in order to achieve a gentle, musical high-frequency boost.

And I thought that, for today, it would be good just briefly to talk about the idea that this is absolutely something that you can do on the bottom end also!

Let’s talk about kick drums again. A common problem with kick drums is that they need a little extra oomph added to the bottom to ground the mix in an appropriately anchoring way — but, when you add that boost, it also adds some subsonic garbage below where you want the impact felt, which muddies things up and makes your master bus compressor overreact.

The solution? You guessed it — pair the bell-shaped LF boost with a corresponding cut to the frequencies below it!

On that same punk song I was talking about yesterday, I did this very thing with the kick drum.

I needed it to speak a bit more around 100Hz, and after some quick experimentation, I found that there was something good happening when I boosted at 102Hz (the purple dot in the pic below). This was a bell-shaped boost of 1.3dB with a Q of 2 — neither very wide nor very tall. Just a little extra missing solidity and definition.

But then the bottom end of the kick drum sounded muddy — oh no! So what did I do to clean it up? I added a low shelving EQ, -1dB at 107Hz (the red dot in the pic below).

And that’s all it took! Just a little contouring.

You might be wondering: why didn’t I use a highpass filter, in the same way that I used a lowpass filter in yesterday’s example? And the reason is that highpass and lowpass filters introduce a fair amount of phase shift around the area where the filter is happening. (This is an oversimplification, but generally accurate for the purposes of this little discussion.)

In the high end, this phase shift can have a lovely “smearing” effect that makes the boost feel gentler and better integrated with the rest of the music. But on the low end, phase shift can have the effect of making a kick drum feel less punchy, less tangible.

So when I’m doing this “boost + cut” trick on the low end, I often opt for a low shelving EQ instead of a HPF — because it introduces less phase shift, resulting in a more solid-feeling definition to the sound.

A house is only as strong as its foundation — jamie