Wavetable synthesis isn’t a new concept: In the ’70s, synthesizers such as Wolfgang Palm’s PPG used digitally stored waveforms as lookup tables. With the capability of sweeping through the tables to produce animated sounds, you could create timbres that went beyond what most analog synthesizers of the time were capable of.
There have been numerous wavetable synthesizers in the software domain, most notably Steinberg’s version of the PPG, Arturia Prophet V, Native Instruments Massive, and MOTU MX4. Xfer Records’ entry into wavetable synthesis is Serum, which manages to combine great depth in programmability while maintaining an intuitive user interface. Serum is available as a download that includes AU, AAX, and VST plug-ins, and I tested it on my 2.93GHz, 8-core Mac Pro using OS X 10.9.5 with 14 GB of RAM.
Serum has four main windows: Osc, FX, Matrix, and Global. Osc tops off with sections for each of Serum’s four oscillators (two main oscillators, plus Sub and Noise). The Sub Oscillator serves up basic analog-style periodic waveforms, which you can transpose up or down by four octaves, so you are not restricted to sub-oscillator functions. You can send the oscillator directly to the output (bypassing filter and effects settings), set pan and level positions, or use it as a modulator for AM, FM, ring modulation, or sync functions.
Fig. 1. The Osc window displays Serum’s two oscillators as well as envelopes, LFOs, and associated parameters. You can drag and drop envelopes and LFOs onto control knobs to modulate their parameters. In addition to sharing the same modulation capabilities as the Sub section, the Noise oscillator has a one-shot mode that is useful for adding attack-transient effects. Used as a transient, you generally wouldn’t want the pitch to change according to the notes played, but you can enable pitch tracking with a click on a button. Additionally, you can set the start time of the noise playback or randomize it.
The Osc window displays the wavetables inhabiting the two main oscillators and harbors what are arguably Serum’s most compelling features (see Figure 1). Although Serum provides a huge menu of wavetables, you can place your own WAV or AIF files into the user Tables folders and load them into oscillators, at which point they will be put into tables and divided into frames: I whiled away hours plundering my sample libraries to take advantage of this feature.
Fig. 2. Among other capabilities, Serum’s Wavetable Editor lets you create wavetables frame-by-frame or by resynthesizing samples. You select a frame to edit from the graphic at the bottom of the editor. The waveform View windows toggle between an animated view of all frames or a single-cycle view. But that is just the tip of the iceberg because Serum includes a remarkably feature-rich Wavetable Editor (see Figure 2), where, among other things, you can select a pencil tool to redraw the waveform, choosing from a palette of shapes including sine, up and down curves, and noise, among others. You can also resynthesize tables as Fast-Fourier Transforms, editing the harmonics for each frame.
Serum lets you build complex wavetables from scratch. If you’re mathematically inclined, you can type in formulas for the synth’s Formula Parser to create a custom table or start from a preset menu of formulas.
Using the above-mentioned features, you can build a wavetable frame-by-frame. Wavetable sounds can transition abruptly from one frame to the next, or you can use Serum’s generous set of tools for smoothing transitions, including crossfades and morph algorithms, phase inversion, and removal of the fundamental.
YOU’VE GOT TO MOVE
Once you have chosen or built your oscillator wavetables, the Osc page provides plenty of ways to add depth and motion. For starters, Unison will add multiple voices of the same oscillator. Use the Detune dial to create a range of sonorities from subtle thickening to atonal clouds of sound. You can fine-tune the amount of detuning using the Blend dial, which adjusts the amplitude of the unison voices against the original voice. The Phase control determines at which point the table will start to play, and you can dial in a degree of randomness to the sample’s start time.
Easily the centerpiece of Serum’s features (or any other any wavetable-based synth, for that matter) is the capability to sweep the oscillator wavetables, and Serum provides numerous ways to do that, from cyclic repetition to random access. In the Warp section, you can regulate the strength of the warpage and select oscillator-sync variations, waveform quantization, as well as amplitude, ring and FM modulation from the various oscillator sources.
Serum has two filters. One is available on the Osc page and governs either or both oscillators. The other filter type affects the output stage of the patch. Serum provides a rich choice of filters, including the usual 1- to 4-pole highpass, lowpass bandpass, peak, and notch types as well as comb filters, flanger-style effects, emulations of classic synth characteristics, formant filters, and so on. In addition to cutoff, resonance, pan, and drive controls, various parameters are attached to different filter types. For example, the more complex multimode filters have a Morph dial while Formant filters have a knob to sweep the formants.
MODULATION AND FX
Right- or control-clicking on any dial opens a menu of modulation choices ranging from Mod wheel and Aftertouch to any of Serum’s envelope generators, LFOs (including Chaos LFOs), and the Noise oscillator. You can drag and drop LFOs and envelopes to destinations, and an indicator appears in their windows showing that they are assigned (with the destination showing up as you mouse over it).
The three envelope generators are AHDSR and, as with most soft synths worth their salt, you can grab any envelope stage and move it on the graphic display or type in precise values. Likewise, you can grab LFO handles and reshape the waveform. A folder provides an assortment of intriguing custom waveforms as well as basic shapes, all of which you can tweak and save into a user folder.
The Matrix page reveals more options for modulation assignments and lets you fine-tune those you have made on the Osc page. For example, you can add curves to the modulation as well as create bidirectional motion and assign auxiliary modulators.
Serum’s solid and flexible FX page includes reverb, delay, flanging, and other modulation effects.
I HEAR YOU
It’s pointless to try to describe Serum’s sound with any accuracy; the instrument’s sonic landscape is truly vast. Suffice it to say that the presets are by turns gritty and distorted or silky and evolving— and sometimes these characteristics can inhabit the same patch.
Everything is laid out in a remarkably logical order. I rarely used the PDF manual to find what I needed. It’s easy to smooth raunchy patches and just as easy to rough up smooth tones. The instrument’s resources are fantastic, and there’s plenty of room for bringing in your own samples and warping the daylights out of them.
With that much power comes a hefty CPU load. To play some of the complex patches, I had to choose a lower oversampling option in the Global menu (though I hardly noticed a difference in sound quality).
Overall, Serum brings together sound-shaping resources from a number of synthesis techniques, including sampling, subtractive, additive, and resynthesis, in a remarkably synergistic instrument. I recommend this synth to anyone anxious to explore exciting sonic territory.
STRENGTHS Powerful wavetable synthesis. Extensive modulation and toneshaping features.
LIMITATIONS Can be CPU-intensive. No standalone version.
Marty Cutler is fond of cats, regional Chinese cooking, five-string banjos, and synthesis, although generally not all at the same time.