Review: KV331 SynthMaster One

Affordable big room synth with massive features
Image placeholder title

While its big brother, SynthMaster, is quite popular with the European trance and big-room market, in the US, KV331’s products fly under the radar. That’s a shame, because their most recent entry, SynthMaster One, offers a wide range of features with an interface that keeps everything upfront and available for tweaking at all times. What’s more, SynthMaster One includes the ability to import waveforms, wavetables, and even MIDI files, and it offers some surprisingly advanced programming options that pros will appreciate.

Structurally speaking, SynthMaster One is incredibly deep. Each of its two oscillators includes a dedicated sub-oscillator that goes far beyond the usual fare. The dual multimode filters offer simulations of classic analog gear and include genuinely versatile routing options, especially for a synth at this price point. The modulation tools cover the basics nicely, with a few thoughtful touches that add to their range. Naturally, the end of the signal chain includes an assortment of now-standard effects for adding polish to the output.

SynthMaster One’s huge routing interface puts its signal path front and center, literally.

Image placeholder title

Most of the SynthMaster One’s components include initialize, copy, and paste, which speeds up the design process greatly. Although a thorough PDF manual is also included, it’s embedded in the synth and is only available via right-clicking. This can be a source of confusion if you look for it on the website or in the installer package, making it challenging to view it on a secondary tablet as you work (on a Mac, the PDF opens in Preview, so with a few steps, you can save it and move it to your iPad). On the plus side, the factory bank of presets is positively enormous and accessed by a nicely designed browser, so you may never even need the manual.


SynthMaster One’s oscillator amenities are practically a synth unto themselves. All of the usual tuning options, including up to 16-voice superwave effects, are present, but the waveform selections are frankly, astounding. In addition to the classic waveshapes, there are sampled cycles from vintage gear such as the Roland SH-101, Korg MS-20, Alesis Andromeda, and quite a few others. While a single cycle isn’t going to create an exact replica of those oscillators, the inclusion of tuning drift and keyscaling (in the Settings area) go a long way toward adding a retro vibe to these waves.

There is also a huge assortment of wavetables that includes just about everything from metallic growls to animated pulse width from some of the classic synths listed above. And for those who like to roll up their sleeves and get dirty with details, SynthMaster One allows you to import external wave data, ranging from single cycle-wave loops to multisampled keymaps. If you’re an Xfer Serum user, you can use it to create original wave-tables, then import them into SynthMaster One for use with its synthesis engine.

That said, these processes aren’t exactly straightforward, as you have to dive into the synth’s folder structure and add the files manually for each imported sample or wavetable. For example, if you’re bringing in a keymapped set of multisamples, you’ll need to re-label each according to its root note (e.g. “Square.A1.wav”). As for wave-tables, each single cycle must be 2048 samples for it to work properly. While these tasks are anything but drag-and-drop, their inclusion extends the value of the synth a great deal for patient designers.

Fig. 1. The dual suboscillators include extensive modulation options, including AM, FM, Ring Mod, and Phase Modulation.

Image placeholder title

Once you’ve selected your waveform source, you can further process it via an Algorithm tool that includes simple filtering, sync effects, pulse-width parameters and bit-crushing.

The sub-oscillators are also a knockout because they are not the usual lower-octave sine or square wave, as in most other synths. For starters, the sub-oscillators offer many of the same single-cycle waveforms as their primaries, with the inclusion of several noise samples, as well.

Additionally, the tuning range covers approximately five octaves in either direction, so it’s possible to apply them as a second oscillator for many applications. The big surprise here is their ability to function as modulating oscillators for the primary oscillator, with options for FM, AM, ring mod and phase modulation (see Figure 1).


The dual filters can be configured in three ways—Series, Parallel and Split—with Split allowing you to use an oscillator, sub-oscillator, and filter as a single signal path, which is great for layering tricks.

The filter types are all based on the standard multimode options—lowpass, highpass, bandpass and notch (called Band-stop here). While there are no morphing parameters or hybrids, there is a wide variety of models available, including ladder, diode ladder and Bite. Input gain and drive parameters are included and subjectively, these imparted a certain hardness to the output, giving the character more aggression than warmth in the majority of my overdrive tests.

There are also Acid and Boost switches that function as you might expect, with Acid doing aquite capable job of imparting a touch of that 303 vibe, especially with the diode ladder. These features definitely give SynthMaster One more of a big-room feel and a distinctive sound.


The Modulation tools include three LFOs and four envelopes, as well as the essential MIDI continuous controllers, such as mod wheel, velocity, Aftertouch, and several others. In addition, there are a few exotic key-triggered resources that can alternate between two values or apply a random value for each note event, which is very handy for pseudo step-sequenced effects. The main LFOs and envelopes include front-panel routing controls for common destinations such as amp and filter, but there are also two modulation matrices for up to 24 additional patch points.

Fig. 2. The attack, decay, and release segments for all four envelopes include individual curve controls.

Image placeholder title

The four envelopes are standard ADSR affairs with individually adjustable slopes for the attack, decay, and release segments (see Figure 2). Two are hardwired to amp, while the other two can be freely assigned. Front-panel access to velocity depth and one-shot mode are added niceties. SynthMaster One’s two main LFOs are fairly sophisticated, with waveform types that include all of the single cycles from the primary oscillators. Dedicated knobs for attack, phase, sample-and-hold, and adding noise are available on both, and of course, there is an array of tempo-syncing amenities, as well. A third LFO that is dedicated to vibrato, offers the user individual depth for each oscillator along with attack and rate, and it is also available on the keyboard panel.


Rounding out the synth’s arsenal is a set of standard effects and arpeggiation tools. The arpeggio-ator has ten modes, including a user-programmable 16-step sequencer. A generous range of note values, including swing, is available for generating syncopated results. As a bonus, you can import .MID files directly into the arpeggiator with drag-and-drop functionality.

Fig. 3. Synthmaster One’s effects include graphic elements, like this representation of the chorus’s resonant peaks, introduced by adjusting its feedback amount.

Image placeholder title

The effects cover all of the basics, with distortion, EQ, compression, chorus/flange, delay, and reverb available (see Figure 3). Although this section’s design looks a lot like the same tools in Sylenth, the processes in this chain can actually be reordered. The distortion includes five adjustable points, each of which has its own Bezier curve, giving it an extended range for saturation tricks. Additionally, the stereo delay offers its own two-band EQ for highpass and muted analog tonalities.


The developers on the SynthMaster One team really took their notes on the current software market by including compatibility with Serum wavetables, adding a Sylenth-like single-page user interface, and giving the user the ability to add drifting analog qualities to the oscillator behavior. With all that said, its sub-oscillator is one of the most original tools I’ve encountered on a softsynth and here’s hoping other developers take note of this innovation, because it’s absolutely fantastic.

As for the big picture, SynthMaster One’s sound is shockingly flexible, and though the filters are a trifle on the hard side, the $79 price tag makes it an impulse buy regardless of your skill level. This is definitely a cool softsynth to have in your collection.

Subtractive/wavetable architecture with extensive filter routing options. Sub-oscillator modes include FM, AM, PM, and ring mod functionality. Huge library of well-organized factory presets.

Importing user waveform data is a complicated process.


Producer Francis Prève has been designing synthesizer presets professionally since 2000. Check out his soundware company at