To add low-end punch to drums in a mix, we often use equalizers to boost bass frequencies. But for the kick drum in particular, there’s another tool we can use to jack up the bottom: the subharmonic generator. Not just more precise, a subharmonic generator can sometimes also sound more transparent and musical than EQ.
In this article, I’ll show you how to use a subharmonic generator, the excellent (and free!) Metric Halo Thump Percussive Subharmonic Synth plug-in, to make your kick drum track sound more powerful—while also reinforcing your song’s harmonic structure.
Fig. 1. Metric Halo Thump can generate multiple subharmonics that sound fantastic on drum tracks. Here, Thump’s two oscillators are tuned to E notes an octave apart. Thump can be instantiated either on an insert for the kick drum track or, for even greater tonal control, on an aux fed by the kick. The plug-in can tune the subharmonics it generates to multiple frequencies of your choosing (see Fig. 1). What we want to do is use the plug-in to tune the kick to the key of your song. For example, if your song is in the key of E major or E minor, make the plug-in generate a low E (the tonic note for the key). Every time the kick drum strikes, the low E that’s generated will reinforce your song’s foundation. And because a discrete frequency is generated, you’ll leave plenty of space in the bass-frequency band for the electric bass to voice clearly in the mix.
The octave in which you choose the subharmonic to be generated is very important. Keeping in mind that our goal is to reinforce the kick drum’s bottom end, the subharmonic should generally fall in the range between C0 (32.70 Hz) and E1 (82.41 Hz). (Go to phy.mtu.edu/~suits/notefreqs.html for an excellent table identifying the frequencies that correspond to musical notes.) That said, there are no hard and fast rules.
Keep these considerations in mind: The lower the subharmonic’s frequency, the less audible it will be on some consumer playback systems, and it will eat up more of your mix’s headroom (all other things, such as volume, being equal). On the other hand, the higher the frequency the more likely it will be recognized as a discrete note and clash with the bass guitar (or sound just plain stupid!).
MIGHT AS WELL THUMP
Fig. 2. Thump's block diagram shows the signal paths for its two oscillators. Thump provides two independent subharmonic generators (Oscillators 1 and 2; see Fig. 2), each of which can attack (voice initially) and sustain at different frequencies as determined by their respective Atk Freq (Attack Frequency) and Sust Freq (Sustain Frequency) controls. For example, Thump’s attack frequency can be set higher than its sustain frequency to make a tom track resonate initially at one frequency and then pitch-bend downward.
Since we want the kick drum to voice only at our song’s tonic pitch, we’re going to keep the Atk Freq and Sust Freq controls for each oscillator set to the same frequency. There’s no rule saying you need to use both oscillators. But if your song’s key is between C and E natural, you can set respective frequencies for the two oscillators that are an octave apart within the optimal 32.70-82.41Hz range I mentioned above.
For example, if your song is in the key of E, you can set Oscillator 1’s attack and sustain frequencies to 41.20 Hz and Oscillator 2’s attack and sustain frequencies to 82.41 Hz (E notes an octave apart). Thump’s stepped frequency selections don’t necessarily correspond exactly to musical notes. To select the precise frequency you want, click on a frequency readout and type in the number of Hz you want to generate.
When generating two subharmonics on a kick drum track, I generally like to use Thump’s Mix sliders to attenuate the higher of the two frequencies around 10 dB with respect to the lower (depending on the dry track’s spectral balance). Doing so keeps the kick from sounding top-heavy.
To avoid causing distortion when closely spaced bass frequencies in wet and dry signals combine, set Thump’s Env Atk (Envelope Attack) control to roughly 2 ms; this will make the subharmonics voice a split second later than the dry signal. Raising the Env Sust (Envelope Sustain) control makes the subharmonics sustain longer in between kick-drum hits; if the bass guitar and processed kick clash, lower the Env Sust control. You can ignore Thump’s Pitch Atk and Pitch Sust (Pitch Attack and Pitch Sustain) controls for this application, as they will have no effect when the Atk Freq and Sust Freq controls are set to the same value.
If you placed Thump on your track’s insert, use the plug-in’s Wet/Dry Mix control to dial in the best blend of original signal and added subharmonics. Placing Thump on an aux—with Wet/Dry Mix set to 100 percent wet—will give you even better control, as you won’t have to attenuate the kick’s beater slap just to get more subharmonic level. Consider that last tip as my, ahem, punch line for this story!
Michael Cooper is a recording, mix, mastering, and postproduction engineer, and a contributing editor for Mix magazine. You can reach Michael at mailto:email@example.com and hear some of his mixes at soundcloud.com/michael-cooper-recording.