LinPlug Spectral additive soft synth reviewed

February 12, 2014

The day of additive synthesis has arrived. Additive is a powerful technology, capable (in theory) of producing absolutely any sound. But while additive synths have been popping up for years, they have long been hampered by two factors. First, until recently computer chips weren’t fast enough to handle the massive computational demands in real time—not without compromises. Second, with potentially hundreds of sine-wave partials to control, the user interface for additive synthesis can be a bit of a mind-twister.

Both problems are now history. LinPlug Spectral does additive, and both the sound and the editing controls are excellent. Spectral demands a fast computer, but if your machine is up to the task, its power will knock you out.


PROS: Deep, rich resources for sound design. Beautifully animated presets. Solid arpeggiator. Band-limited tone generator is free of aliasing. Elegant user interface.

CONS: Needs a fast CPU. A few more matrix modulation routings would be nice.

Bottom Line: A dream come true for sound designers, and a potent resource for any well-equipped studio.

$149 street |



A Spectral sound uses up to four oscillators, each with its own filter. Cross-modulating one oscillator or filter with another is also allowed, and a clever band-limiting algorithm prevents the AM and FM from producing aliasing artifacts. Each oscillator can be spread into a six-voice unison with detuning, and each oscillator/filter sub-voice runs in stereo, so various components of a complex sound can be panned to different locations.

Eight of the 12 envelopes are assigned to amplitude and filter cutoff for these four sub-voices, but there are 15 envelopes total, all of them available as modulation sources in a matrix mod section with 15 slots. There are also five LFOs.

With so many sources to choose from, having 15 slots in the mod matrix doesn’t seem like enough. Fortunately, you don’t need to use the mod matrix for routing the filter and amp envelopes to their respective sub-voices, nor for audio-rate modulation of an oscillator or filter.

The envelopes are AHDSFR—the H stands for a hold stage and the F stands for a fall rate in the sustain stage. Attack, decay, fall, and release curves can be adjusted smoothly from logarithmic through linear to exponential. The LFOs can be cranked well up into the audio range.

Rounding out the picture are a very capable 32-step arpeggiator and six slots for effects. The output of each sub-voice can be routed to the inputs of up to two different effects, with a balance control, and the effects topology can be configured in various parallel or series shapes, so you can easily do complex signal routings.

The effects selections include most of the usual suspects, including a bit-crusher. The list doesn’t include overdrive/distortion, but the filter effect (separate from the sub-voice filters) has a girth-inducing overdrive knob.

Spectral is a bit of a resource hog. The CPU usage meter in my DAW told me a four-note chord was using more than 50 percent of my Intel 2.67GHz Core i5 CPU. Windows Task Manager revealed a less disturbing picture, however: A single instance of Spectral seems to use only one of the cores in my quad-core CPU. When I loaded a second instance of Spectral and laid down a second track, it was assigned (presumably by the DAW) to a different core. As a result, two tracks didn’t bump the DAW’s CPU meter any higher than one track.

The Additive Engine

The core of the Spectral concept is a graphic editor for each oscillator and filter. In the image at left, each green bar shows the amplitude of an additive overtone. Octave divisions of the spectrum are shown in slightly contrasting dark and light bands. Preset spectra can be loaded and then blended with the user-edited spectrum. You can specify the loudness of each overtone by dragging with the mouse. To save CPU cycles, Spectral isn’t actually mixing the partials with one another in real time. Each time you edit a waveform in the spectrum editor, the synth recalculates it. The calculation takes a fraction of a second, after which the new wave is displayed in the upper window as a typical squiggly contour.

In fact, each oscillator has two waveforms, each with additive editing. The two can be blended with a mix knob. There’s also a symmetry knob, which biases the waveform to the left or right, adding overtones. Both mix and symmetry can be modulated from an LFO or envelope, so you can get some very animated tones from one oscillator with no filter.

A filter’s response curve can be edited in exactly the same way, one partial at a time. Extremely complex comb filtering is easy to set up, as is a lowpass or highpass filter with any roll-off slope. The resonance knob exaggerates the distance between the peaks and dips in a filter’s response curve.

The edit window for partials has several macros for setting up useful contours. You can add even or odd harmonics, for example, select a range of harmonics and drag them up or down together, or transpose the entire spectrum up or down in octaves. A set of templates is included, so if you want something like a square wave or a dark sawtooth, you can load it from disk.

Sound Library

Spectral’s factory preset library boasts more than 20 categories. The “Bass” and “Pads & Chords” sections each have more than 100 patches; others have only four or five. Most are programmed to respond to the mod wheel in expressive ways. You won’t find much in the way of realistic keyboard emulations, however. Spectral is about fresh sounds, not classics.


Spectral’s arpeggiator is packed with options. Each of the 32 steps can have its own gate time, velocity, transpose, and glide on/off setting. When some steps are transposed, a single finger on the keyboard can play a pattern such as a bass line, complete with ties and rests. When you’re holding a chord on the keyboard, you can assign each step to play a given note from within the chord.

The global controls include several up/down choices, swing amount, rhythm step size, gate time, the number of steps in the pattern, a knob for blending the played velocity of individual keys with the programmed velocity for steps, and so on. You can set the arpeggiator to “mod only” mode, which will route its velocity settings to the modulation matrix without using its note data, thus turning it into a flexible trance gate generator. (There’s also a stereo trance gate in the effects section.)

Other Features

Overall, the user interface earns high marks. Each section of the panel has its own tools button, which opens a simple menu containing copy/paste and initialize commands. Arpeggiator presets can be loaded or saved from this menu, and the spectrum editor has several extra commands, such as generating a random set of overtones. Single modules (oscillators, filters, effects) can be turned on or off with a single right-click, which aids in sound design.

A few important parameters are tucked away on a separate Options window. Here you can switch pitch-bend response on or off for individual oscillators or filters, load microtonal scales (yay!), adjust the velocity response curve, remap incoming modulation wheel and aftertouch messages to a different MIDI message type, and a few other things.


Within a couple of hours after I started using it, Spectral leaped up into my short list of stellar VST synths. (That list is getting a bit crowded by now, but never mind that.) LinPlug didn’t cut any corners with this instrument—it’s a brilliant achievement. It sounds terrific and offers rich rewards to sound designers.

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