Sound Design: Adding It Up—Understanding and Exploring Additive Synthesis

Understanding and exploring additive synthesis
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Understanding and exploring additive synthesis
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Last month, I used Ableton Operator to demystify the intricacies of FM synthesis. This month, I’ll use it again to shine a light on additive synthesis, which can appear just as complex. But it is easy to understand once you grasp the core principles. Additive waveform generation is a very powerful tool, especially for creating vintage digital textures; instruments ranging from the New England Digital Synclavier to the Kawai K5 (from 1987) relied on it as a source for their unique, crystalline sounds.

The coolest thing about experimenting with additive synthesis is that you quickly develop a deeper understanding about sound itself. And because these techniques are equally applicable to other additive synths (for example, Xfer Records Serum), once you get the hang of a few essentials, you can start using that knowledge in different contexts.

Basic Shapes. One of the first things to understand about additive synthesis is that it gives you direct access to discrete harmonics. For example, common analog waveforms, such as sawtooth and square, can be easily created: A sawtooth consists of all integer harmonics descending in volume as they get further away from the fundamental, whereas a square features only the odd harmonics descending in a similar manner. But that’s just the tip of the iceberg.

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Emulating Organs. Many electronic-music historians refer to the Hammond organ as the first mass-produced instrument that offered additive synthesis, since the drawbars correspond to the lowest harmonics in the series. Accordingly, by sticking with the first eight harmonics of your software additive synth, you can create organ-like textures. As I mentioned in my August column on sine waves, the best starting point is to have a strong first and third harmonic. From there, it’s a matter of tinkering with the other six harmonics to simulate different drawbar settings.

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Vocalization. Most additive softsynths allow you to sculpt the harmonic spectrum quickly with simple mouse gestures. A decade ago, with an understanding of formants in place, I discovered that by carving out swaths of harmonics while emphasizing others (in a peaks-and-valleys manner) vowel sounds can be generated. In the first Operator screenshot, the harmonics create an “Ahh-Ohh” timbre. The second example sounds more like “Eeee.” Use those as starting points for your own experiments.

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Bells. Another insight that can be gleaned by working with additive synthesis tools is that bell and chime textures consist of only a few, widely spaced single harmonics. The guideline here is to keep things sparse and if you want a bit more chime-like dissonance, slightly raise the value of a few adjacent harmonics.

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Hybrid Textures. Many ’80s-era digital synths included waveforms that were hybrids of vocal and bell sounds. To re-create these, start with a vocal spectrum then add a few single harmonics using the bell approach. The results will be reminiscent of some of the PPG Wave 2 and Korg DW-8000 waveform options.

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