Trigger Warning: Kick Drum Layering with Eurorack Modular

There have been countless words written about kick drum synthesis and layering kicks within Ableton and Logic (in these pages and elsewhere), so I thought I’d try and bring something new to the table.

The advantages of layering your kicks (and other drums for that matter) are well documented, but in short it allows us greater control of the duration, pitch and low-end content of our bass drums.

In the MIDI world, drum synthesisers like Nicky Romero’s Kick Synth and BazzISM vst provide a great deal of sonic accuracy, but what if we’re using audio as our source? Audio to MIDI conversion algorithms have made good progress in recent updates to Logic and Live but it’s a bit fiddly and tends to require some degree of tweaking.

Bass Kick Instinct

In a mixing class I was teaching yesterday, dealing with some drum stems from a neo-soul recording, the topic of using an oscillator to deepen your kick cropped up. Logic’s own Sub Bass plug-in and Waves Renaissance Bass are two options on the market, but for a greater deal of control I introduced them to the Test Oscillator.

This is a free-running oscillator capable of producing sine and pulse waves as well as various types of noise at whichever frequency you specify. We added this on a new software instrument track, tuned it to an octave below our kick’s fundamental and used the original kick to open a gate using sidechain analysis. Pretty simple stuff.

This is fine but there are essentially two pitfalls we can run into. The first is that the oscillator is free-running, meaning its phase is all over the shop. This can not only lead to annoying clicks and pops but it can also lead to inconsistency in the perceived volume of our sub kick. Below is a sine wave at 40 Hz opened by a sidechained gate: we can clearly see from the three instances that none of them share the same starting phase.

The second issue we run into is the test oscillator is a static pitch, and all good kick drums have an audible drop, or sweep. This what creates the snappy transient at the beginning and deeper tones at the end. Giving it some thought I figured I could use my Eurorack setup to get close to a useable kick oscillator and integrate it with my DAW of choice.

Trans Eurorack Express

I’m going to demonstrate how to use my Eurorack modular to not only trigger a sine wave from my DAW from an audio source but also add separate amplitude and pitch envelopes and restart the oscillators phase when the gate is high.

Let’s start off in Ableton Live. I’ve pulled in a mono kick and snare and stereo overheads track. We’re working at 128 bpm. I’ve done virtually no processing to these tracks, except gate the kick and snare to ensure their signal is cleaner before triggering any external gear:

Here’s the kick in solo. It sounds okay, and with some EQ and compression we could get it sounding a little fuller, however it doesn’t really contain all of the necessary frequencies for a modern RnB recording:

I’m going to mute the snare and overheads so we can concentrate on our kick drum. The principle of this sound is as such: we’re going to send a duplicate of our kick out of the computer into a module that will create a trigger based on the incoming signal.

We can feed that into an envelope for our amplitude and pitch modulation which will modulate a VCA and oscillator, respectively. This can then be fed back into Live and summed with the original kick.

Oscillate Wildly

Let’s determine what our original kick is doing before beefing it up. I’ve loaded up the excellent Voxengo SPAN on to the track. We can see our kick is sitting at around 55 Hz (a low A if anyone’s interested).

Top tip: have a peek in the Edit page to adjust the Block Size and Avg Time for a more resolute image.

Let’s get a signal into our DAW. I’ve created a blank audio track (cmd + t), taking a sine wave from a Doepfer A-110 Standard VCO into a Doepfer A-131 Exponential VCA into Live on input 1 on my sound card. I’m using a Focusrite Saffire PRO 14 for this, as it has multiple outputs (which we’ll need later).

Set the newly-created channel to input 1 and the monitor to ‘In’. On the VCA turn the gain up, as we have no CV coming in at the moment.

I’ve added a new instance of SPAN on to our sub and tuned my oscillator to around 55 Hz. The Doepfer A-110 doesn’t have the widest range for the Tune pot so I’m using a DC offset from my Make Noise MATHS channel 2 to get it exactly where it needs to be – be careful though, it’s sensitive!

As you can see it’s not a perfect sine wave: we have all sorts of other harmonics there, likely caused from running a hot Eurorack signal into a line level input on my sound card, but it’s not the end of the world. Let’s move on to the trigger.

Trigger Warning

Start off by creating a send/return track (alt + cmd + t) and name it ‘Trigger’ or whatever you want. Send the kick to it at full volume, or however loud you can get it without clipping. Route your send out of the next available output, which in my case is output 3.

I’m taking this copy of our kick into a Doepfer A-119 External Input/Envelope Follower using the Asym. In input, which is line level. The other input, Symm In. is for instrument level signals (guitar or similar), audio straight out of the soundcard would be too hot for this and we’d experience a great deal of clipping. From the A-119 I’m taking the Gate Out to a Doepfer A-180 Multiple, so we can duplicate the signal.

I’ve taken the first copy of the signal to a Frequency Central System X Envelope, which I think is one of the best sounding envelopes for short, snappy sounds like drums, with a short decay and release with no attack or sustain.

The Norm output is routed to open my VCA. Be careful to fiddle with the CV, input and output amounts on the VCA to get a nice clean signal that’s not clipping. Voila! We now have a triggered sine wave. Adjust the decay and release to match your original kick. Here’s the sine kick in isolation:

…and here it is balanced with the original kick:

It’s sounding okay but a bit rudimentary, and not drastically different from what we could already achieve with Logic’s test oscillator, so let’s move on.

Phased and Confused

Phase is the starting point of a waveform, normally described in degrees. 0º is the point at which we think of a sine wave starting at, going from 0 to a positive amplitude, where it peaks at 90º, then passing 0 again would be 180º. The lowest trough is 270º and then the cycle is completed.

As with the Logic Test Oscillator, we have an issue with our phase: our A-110 is free running and we need to sync the phase when the gate is high. We can do this by taking a duplicate of our gate trigger from the multiple and plugging it into the Sync input on the oscillator.

Here you can compare two versions I made of a loop, the first with no phase sync and the second synced to the gate on signal – every time a gate on is received, our oscillator’s phase is reset to 0º.

Pitcher This

The next logical step would be to modulate our pitch as it’s static, and that’s not really what kicks sound like. To simulate the beater striking the skin we can use a pitch envelope. I’ve taken another output from the multiple and plugged it into the trigger input on MATHS channel 1.

MATHS is a fantastic module with a plethora of material written about what you can do with already. Channels 1 and 4 are what are called function generators, which can be used as envelopes or LFOs. What’s nice about these is the ability to change the curvature from logarithmic (slow fade) to linear (straight fade) to exponential (fast fade), giving us far greater control over our envelope.

The output of channel 1 is plugged into the CV2 input of the A-110, which is attenuating the pitch modulation. Using a Rise (attack) time of nothing, adjust the Fall (decay/release), ‘Vari-Response’ (curvature, form logarithmic to exponential) and channel 1 attenuvertor on the MATHS to taste.

Increasing the CV2 amount on the A-110 will give us a thud/thwack at lower values and something closer to a zap at maximum values (this essentially does the same thing as the attenuvertor). Below is a sketch of the final patch.

Here’s how the kick sounds solo’d:

…and here’s how the pitch envelopes sub kick sounds with our acoustic:

…and finally in the context of the loop, with some light compression added:

For comparison, here’s the original loop:

Taking it Further

Once you’re receiving a trigger from your DAW and are able to record the results back in you’re laughing. There are many dedicated drum modules that could function in place of the A-110, and even many oscillators dedicated to low-end replication, such as the Make Noise STO.

I’ve taken the example further by swapping out my oscillator for the multi-functional Expert Sleepers Disting using the VCO with waveshaping (mode 4-d). MATHS is now controlling the frequency modulation, and we have an FM sine similar to the Musical Mob Pulse X kick drum – just add some overdrive and you’re there!

Here I’ve used the Music Thing Modular’s Turing Machine as a strange 8-bit wavetable synth, using a Doepfer A-145 LFO running at audio rate to clock the Turing Machine. Sounds like a hollow Game Boy-type sound:

In fact, combining envelopes with anything that has a CV-able input and can be tuned low enough will get you a half decent-sounding kick. You can experiment with clock multipliers and dividers to get stranger overtones.