Kirnu Interactive has launched ButterSynth – an iOS synth that could revolutionise what it means to make sounds on your iPad.

Kirnu Interactive is a small developer based in Finland with only one instrument released previous to ButterSynth. That being said, ButterSynth is one of the most feature-rich iOS music apps I’ve seen, and there’s something for every synth enthusiast, sound designer, and electronic musician.

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ButterSynth for iPad

ButterSynth is a hybrid synthesizer that flexes wavetable, FM, granular, and sample-based synthesis with a total of 6 oscillators. Further, this hybrid synthesizer is a standalone synthesizer for iPad, and the developer promises it’s capable of a “vast sonic range, from gentle pads to screaming leads and basslines”.

In practice, you can mix the wavetable, FM, sample and granular engines and layer them together to create huge sounds. You can access each of these engines on the left-hand side of the interface with labelled buttons, as well as activate white & pink noise generators.

Its dual-wavetable engines feature 9 phase modes, wave folding, and unison controls akin to popular synths like Vital & Serum, in addition to a wavetable editor so you can hand-draw any adjustment to a wavetable as you see fit (supporting up to 256 frames), and you can make your own wavetables too!

Meanwhile, ButterSynth’s FM engine gives you 4 operators with a selection of 12 modulation paths. You can load each operator with any waveform from the default library or import your own, and the inclusion of a feedback parameter means the operators can modulate themselves too.

Both the sample and granulator engines allow you to import your own samples or use those from the default library too. Then, these engines give you controls to chop, trigger and layer those samples, and these engines also offer the same unison as the wavetable engine.

After you’ve created your layers, you can configure the 32-slot modulation matrix and modulate each layer as you see fit. You can assign modulation to any parameter by long-tapping it, and the developer notes that the matrix “[features] precise mix/max ranges, self-modulation (via the amount target), plus configurable response curves and layer modes”.

Furthermore, modulation sources include 4x MSEG-style looping curve envelopes, 4x LFOs, 4x step sequencers, an X/Y pad with motion recording, filters, and 8x Macro dials. There’s also an arpeggiator to inspire your performance if that wasn’t enough!

The icing on this rather large, buttery cake is the onboard FX rack. Here, you can insert and create effect chains with ButterSynth’s 16 built-in FX modules. The developer notes that, at launch, modules include delay, reverb, distortion, chorus, OTT compression, and more. You can modulate the parameters of these effects and program ‘per voice’ modulation effects too!

Finally, ButterSynth comes packed with hundreds of ready-to-use presets, wavetables, and samples which are stored in the Files app on your iPad. This is so that bulk import/export, backup and community sharing is as seamless as possible.

One iOS synthesizer that is beloved by so many is BASSalicious 2 which is a wavetable synthesizer with four oscillators. I would argue that BASSalicious’s interface is more delicious than ButterSynth’s, but BASS doesn’t offer quite as much functionality as Butter. So, is Butter the next fan-favourite iOS app?


Kirnu’s ButterSynth is available as a standalone synthesizer in AUV3 format for iPad from April 28th.

The developer also has a paid synth for Windows & Mac, Cream.