Elastic OSC review: iOS polysynth takes the Mutable Instruments algorithms on a wild trip

Elastic OSC is the latest Synthesizer app from developer Oliver Greschke that takes the Mutable Instruments algorithms on a wild, modulating trip.

This review begins in 2018 with the release of the Mutable Instruments Plaits macro oscillator, which quickly became one of the most popular Eurorack modules. Then, a move that spoke volumes: The DSP code went open source under the MIT license, allowing third-party developers to use it for other projects.

Among the most famous adopters is Arturia, which implemented some oscillators into the MicroFreak without prior agreement and later with. The module’s discontinuation and the end of Mutable led to a flood of Synthesizer projects using Plaits DSP code. 

Elastic OSC project by Oliver Greschke (developer of Elastic Drums, MoMinstruments) is the most recent project to utilize these legendary algorithms.  After Elastic Drums, FX, and Melody, this is the fourth Elastic app by the German developer.

Elastic OSC

It’s a polyphonic Synthesizer for iOS with a classic subtractive signal flow, consisting of an oscillator block, filter, envelope, and a multi-effects section. Of course, you usually can’t convince synthesis fans with a 1-oscillator synth in 2025 unless it’s a Roland SH-101, TB-303, or Juno emulation.

It is different here for two reasons: first, the oscillator has umpteen morphable facets, and second, it is embedded deeper into the instrument than any other 1-oscillator on the market.

The oscillator core borrows the DSP sound engine from the open-source Mutable Instruments Plaits. It must be noted that Oliver explicitly disclosed the MIT license and Emilie’s copyright in the app’s about section. This is positive, and everyone who uses the codes should do this.

Elastic OSC offers all 24 algorithms of the popular macro oscillator. These include those released with the original hardware from 2018 and those added via updates. They range from virtual analog synthesis, 2-OP & DX-7-style FM, wavetable, granular, modal resonator, drum synths, and more.

The unusual wave terrain synthesis and the mighty DX-7 engines from the last massive update to the Plaits module are also playable. However, you can’t load custom terrain files or 6-OP DX patches like you can with the module’s firmware. I don’t know if Oliver could implement this in the app in the future, but it would be a great add-on.

Playful Mutable Instruments Oscillator Timbres

Like in the module, each synth engine has four main parameters to tweak: frequency, timbre, harmonics, and morph. These parameters are mapped to the X/Y pad or the left/right slider in two groups. You can customize these mappings at any time. 

The controls are in a size and dimension where the touch harmonizes perfectly with them. Praise must go to the UI designer (Gösta Wellmer) who managed to transfer the classic knob configuration to the touch enviroment and solve it just as elegantly as it was in the module.

This oscillator’s vast sound spectrum should be familiar to many after the numerous Plaits code ports (Behringer Grind, MicroFreak, MiniFreak, etc.). It ranges from classic and organic to noisy and experimental.

Remember that the Mutable Instruments Plaits module is a colorful macro oscillator and a complete synth voice. The latter is made possible by its built-in modulation source and low-pass gate, which the developer also incorporated into the Elastic OSC app.

The corresponding parameters are under the X/Y pad: lowpass gate with decay control and modulable timbre, FM, morph, and harmonics (LPG color) parameters. They give the sounds more depth and roundness. As a bonus, the oscillator engine has various selectable output modes. 

Output A is standard, while Output B offers an engine variation. For example, the string model (12) algorithm gives you a raw exciter signal in the B mode. Alternatively, you can mix both together (A+B) or use a L/R panned mixed signal (A/B). 

Master Effects 

A classic ADSR amp envelope, also available here as a shaping tool, ultimately decides whether the sound will be bass, lead, pad, or other. 

Look at the right side; you will find the multi-FX section comprising six creative effects: five-mode distortion, high/lowpass filter, chorus/flanger, delay, and reverb. They are in five different tabs, each with its own X/Y with mapped parameters for real-time control fun.

The effects sound high-quality. They aren’t as good as Eventide or Strymon, but they can compete with classic bread-and-butter effects. One or two more filter types or even some wilder effect types would be desirable. 

You prefer less or more effected sound? No problem. The amount of each effect can be individually adjusted in the dedicated effect mixer. Plus, there is proper gain control and a limiter if you want to explore the app’s dark, noisy experimental side. 

But don’t be fooled. The effects are far more than just a polishing tool. The next part of this review will discuss this.

Elastic Engine

Play sounds with the built-in keyboard or with any other external MIDI keyboard—note by note, chord by chord, or with the flexible arpeggiator. There are various arp modes, rates, and octave ranges to choose from, and for more advanced patterns, there is a skip note functionality. A sequencer is missing.

Two words: Elastic and OSC. We all know how elastic the Plaits macro oscillators have been for a long time. Oliver Greschke of MoMInstruments has taken this elasticity to a new level by implementing his unique elastic engine from his other apps (Elastic Drums…) into the synth’s core. 

In simple terms, the engine allows you to record almost all parameters in real time in a sequence with a length of 1, 2, or 4 beats. Unlike other apps or hardware synths, the parameter automations aren’t connected to a note sequencer.

In this Synthesizer app, they run freely and can be added at any time. Of course, you can play the synth traditionally and tweak parameters on the fly. The second option is way more fun and unique: you play the notes/chords while the automation runs simultaneously.

Press record and play to capture the parameter automations. This works parameter by parameter or all at once. As long as the sequencer is armed, you can save new animations. Deleting them is just as easy. 

Once captured and activated with the record and play buttons, this turns a simple synth sound into a highly complex soundscape. Depending on how slowly or quickly you program the parameters, you can introduce subtle fluctuations into a sound, beautiful on pads, or create radical, noisy transitions and tornadoes.

More Elasticity? 

Both oscillator and FX parameters can be automated to the same extent. When used with the elastic engine, this turns the effects into impressive sound shaping tools that are more than just finishers/polishers.

So far, modulation is only possible when the internal 4-bar sequencer runs. I’d like to see a one-trigger mode in a future update, where you can trigger automation sequences with a key press.

The modulation lasts depending on how long the note is pressed. Capturing several automation slots and then recalling them in a round robin fashion would also be a neat, inspiring feature.

The elastic engine of Elastic OSC is a lot of fun and brings new life to the famous Mutable algorithms. But you can still build on and continue this idea, which I hope will happen. I had the opportunity to beta test the app for a while and still enjoyed it. It inspires me every time I open it.

AUv3 support is also available for big, more intensive iOS recording sessions. For this, I use the ingenious AUM mixing/audio unit host app, which allows me to play multiple EOSC instances and immerse myself in a massive parameter modulation flow.

Sound Demo

I recorded a few nightly jams as sound impressions. The demo contains more subtle but also wilder, noisier patches.

Elastic Drums Review Conclusion

Oliver Greschke and his contributors developed a fun, lovely Synthesizer app. Many will surely say: “Oh wow, another synth with the MI algorithms”. Well, that’s true, and I agree with you.

The key to its special appeal and entertaining nature lies in incorporating algorithms within the Elastic engine. This wild approach enables users to explore the oscillators dynamically and engagingly. I have never seen the Plaits oscillator used that way outside the modular sphere. It’s definitely more than just another MI Plaits-powered polysynth.

A nearly perfect app. I’m missing two things: First, I’d like a one-trigger mode for automation, making it even more fun. Second, an AU version for Mac. The latter will be available soon. MoMinstruments is developing a Mac/Windows version with VST and AU support that will be available shortly.

Elastic OSC is available now on the Apple App Store for $12.99 (US) / €14.99 (EU) / £12.99 (UK). It runs as a standalone universal app and an AUv3 plugin on iPads and iPhones.

More information here: MoMinstruments/ Apple App Store 

iOS Review