Sound Design: Harmonic Sequencing

Keeping it fine-tuned with microtonal wavetables in Xfer's Serum synth
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An ever-increasing number of mainstream synths are supporting microtonal tuning these days. On the hardware side, Korg’s Monologue includes a set of the most common tunings, as well as user-created scales. On the software side, synths ranging from Alchemy to Zebra provide access to custom scales.

While getting the hang of composing with microtonal tunings can be daunting, there’s a simple way to experiment with one of the more common flavors: Harmonic sequencing. Although the standard 12-tone equal temperament scale is essentially based on the harmonic series with caveats for each key, working directly on harmonic sequences offers a tonal purity that’s immediately enticing for some artists.

Fig. 1

Fig. 1

Fig. 2

Fig. 2

Xfer Serum’s additive wavetable creation tools allow a direct approach to designing harmonic sequences, and its Harmonic Series factory wavetable scans through each harmonic independently, based on the Wavetable Position parameter (Fig. 1). Accordingly, modulating it with an LFO will instantly deliver arpeggio functions. For example, a rising sawtooth using a low modulation depth will behave like a traditional upward pattern (Fig. 2).

Going a bit further, you can construct harmonic sequences in Serum by arranging simple wavetables that rely on an isolated harmonic for each index. Because the pitch of each harmonic in the series rises linearly, it’s best to stick with the first eight to sixteen harmonics, as those above it are often too high for musical applications (though they’re useful for “glittery” effects).

Fig. 3

Fig. 3

STEP 1

Initialize a wavetable, and then select a single harmonic and raise its volume to maximum (Fig. 3).

Fig. 4

Fig. 4

STEP 2

Click on the plus sign in the next index and isolate a different harmonic, raising its volume to maximum (Fig. 4).

Fig. 5

Fig. 5

STEP 3

Repeat the process until you have a short array of harmonics around 4 and 16 steps in length (Fig. 5). Working with smaller sets of harmonics gives you more control over your sequences when applying LFO modulation.

Fig. 6

Fig. 6

STEP 4

Once you’ve selected your harmonic set, do not apply any of the table morphing options (crossfade, spectral), as keeping each harmonic as a discrete step is crucial for this technique. When you’re done with your table, the results should look like Figure 6.

STEP 5

At this point, you’re ready to apply an LFO to the Wavetable Position parameter by dragging it onto its knob.

Fig. 7

Fig. 7

STEP 6

Whether you’ve created your table by configuring successive harmonics or composed a pattern in advance by ordering your harmonics according to your desired sequence, the LFO amenities in Serum are the key to constructing the pattern. Experiment with the factory collection of LFO shapes — or devise an original stepped pattern by holding the Shift key while dragging your steps into place. Here, the grid size will determine the note value for each step, in conjunction with the overall LFO rate (Fig. 7).

As you explore these concepts, you may find that the results are reminiscent of early Kraftwerk tracks. Personally, I was startled by this discovery, but then again, Kraftwerk were always light-years ahead of their time.