KORG iMono/Poly vs ButterSynth
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
KORG iMono/Poly
Experience a classic analog synthesizer reborn on iOS. This app faithfully reproduces the iconic 4VCO sound engine, offering deep sound design capabilities with virtual patches and multi-effects. Seamlessly integrate it into your music production workflow.
- Faithful reproduction of classic 4VCO analog synthesizer
- Deep sound design with extensive modulation
- Eight virtual patches for expanded sound potential
- Two multi-effect units
- Quick access to all synth parameters
- Integration with KORG Gadget
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Reviving a classic KORG analog synthesizer. The iconic 4VCO synthesizer, reborn on iOS. The Mono/Poly analog synthesizer appeared in 1981 at the same time as the acclaimed Polysix. Not only was it a fat-sounding four-VCO monophonic synthesizer, it featured a revolutionary design that allowed it to also be used as a four-voice polyphonic synthesizer, which helped cement its legendary status. The long-awaited “KORG iMono/Poly” iPad/iPhone app completely reproduces all features of the original Mono/Poly. Four VCOs and a rich array of modulation allow a wide range of detailed sound design. New functionality such as two multi-effects units and eight virtual patches are also provided. In addition, the seamless integration that you expect from KORG’s iOS apps will fit perfectly into your music making process. The Mono/Poly has been reborn for today’s world, bringing you a unique and legendary sound. * Due to differences in CPU speed of iPads / iPhones, iPad 3rd gen/2/iPad mini/iPhone 4s are not supported, only iPad Air/iPhone 5s or later is recommended. [ Features ] • Deep 4VCO sound. A complete reproduction of the classic Mono/Poly The Mono/Poly synthesizer featured four VCOs, a dedicated envelope generator for the VCF, and also sync and cross-modulation, earning it a reputation for its detailed sound-shaping potential and its distinctive character. • Powerful virtual patches, and the latest presets to catch the scene Eight virtual patches provide the ultimate expansion of the Mono/Poly’s distinctive sound-design potential. Two multi-effect units are also provided, allowing you to create complex and broad-ranging sounds with complete freedom. • Quick access to all panels Although iMono/Poly provides a vast number of parameters, it’s designed with a screen structure that provides quick and seamless access to all of them. With a single tap, you can rotate between the main synth & key assign screen and the virtual patch & effect screen. There’s no need to open individual screens for specific functions, or to move back and forth between them. • Produce music in conjunction with KORG Gadget iMono/Poly can be used in conjunction with “KORG Gadget,” the music production DAW app that has won numerous prizes within Japan and around the world. When you install both apps, iMono/Poly appears as the “Montpellier” gadget within KORG Gadget. More info at korg.com
ButterSynth
This powerful synthesizer app offers a hybrid approach, combining wavetable, FM, and sample-based synthesis. Create unique sounds with a vast sonic range, advanced modulation, and a built-in effects rack. It caters to both experienced sound designers and beginners with extensive presets.
- Hybrid 6-oscillator synthesis (wavetable, FM, sample)
- Built-in wavetable editor
- FM engine with 4 operators
- Sample and Granulator engines
- 32-slot modulation matrix
- Internal FX rack with 16 modules
- Extensive preset library
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ButterSynth is a hybrid 6-oscillator wavetable/FM/sample-based AUV3 and standalone synthesizer with a vast sonic range, from gentle pads to screaming leads and basslines. Mix any combination of wavetable, FM, sample and other synthesis engines for one truly massive sound. For the more advanced users, you'll love using ButterSynth's thoughtfully designed interface, incredibly powerful modulation matrix, fully-featured internal FX rack, factory waveform and sample libraries, and almost limitless scope for fun, experimentation and sound design. For less experienced synth programmers, ButterSynth includes a library of hundreds of ready-to-use presets, sparking your creativity to start making music right away. Headline features include - Mix and match any combination of 6 synthesis engines to either emulate your favourite synths of yester-year or build a synth ready for the future. - Dual-wavetable engines also feature 9 phase modes, wave folding, and deep unison controls modelled on vintage hardware synths. - Built-in wavetable editor gives you the ability to tweak, morph, and hand-draw your own custom wavetables, with each wavetable supporting up to 256 frames. - FM engine offers 4 operators with a selection of 12 modulation paths. Each operator can be loaded with any waveform from the factory or user library, and can also self-modulate via the feedback dial. - Sample and Granulator engines both let you load samples (either imported or from the factory library) and control precisely how they are chopped, triggered and layered. Both also feature the same powerful unison modes available in the WT engine. - Highly configurable 32-slot modulation matrix featuring precise mix/max ranges, self-modulation (via the amount target), plus configurable response curves and layer modes. Simply long-tap any parameter to set it as a Mod destination! - Full suite of versatile control sources which includes: 4x MSEG-style looping curve envelopes, 4x LFOs, 4x step sequencers, X/Y pad with motion recording, 8x Macro dials and a powerful arpeggiator inspired by Kirnu Interactive’s Cream. - The EFX rack lets you build your own insert effects chain using any combination of the 16 built-in FX modules. Modules available at launch include delay, reverb, distortion, chorus, OTT compression etc. Note - FX parameters can also be targeted by the mod matrix, unlocking the possibility to program ‘per voice’ modulated effects. - All presets, wavetables, samples and other settings are stored in the Files app, making bulk import/export, backup and community sharing quick and easy. - All of this is housed in an irresistibly designed 4-tab UI that makes synth programming quick and fun.
Screenshots
Verdict
The clearest difference is price: ButterSynth at $19.99 against KORG iMono/Poly's $29.99. ButterSynth also leads on in-app purchases (none vs 1). KORG iMono/Poly's advantage is rating (4.3 vs 4.0) and iOS requirement (9.3 vs 14.0). On review sentiment, ratings volume, update cadence and ads there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
KORG iMono/Poly costs $29.99 and ButterSynth $19.99 up front. KORG iMono/Poly sells 1 one-off in-app purchase. ButterSynth asks for nothing beyond the download.
KORG iMono/Poly holds the better App Store score, 4.3 against 4.0. Both are backed by a comparable volume of ratings — 85 and 63 respectively. Written reviews point the same way: 62% of KORG iMono/Poly's written reviews are positive against 59% of ButterSynth's.
Both ship on a similar rhythm, roughly every 2 months. The most recent releases landed on November 4, 2026 and November 3, 2026 respectively.
| Parameter | KORG iMono/Poly | ButterSynth |
|---|---|---|
| Price | $29.99 | $19.99 — better |
| Rating | 4.3 (85 ratings) — better | 4.0 (63 ratings) |
| Positive reviews | 62.4% of reviews — better | 59.2% of reviews |
| Number of ratings | 85 — better | 63 |
| Update frequency | Every 2 months | Every 2 months |
| Ads | No | No |
| In-app purchases | Yes | No — better |
| Monetization | Free with in-app purchases — better | Paid |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Requires iOS | 9.3 — better | 14.0 |
| Further details — not scored | ||
| Size | 203 MB | 468 MB |
| Age rating | 4+ | 4+ |
| Developer | KORG INC. | Arto Vaarala |
Customer experience
KORG iMono/Poly
ButterSynth
User reviews
KORG iMono/Poly
From 85 App Store ratingsWhat we love
- 🎶 Great sounding synth
- ✨ Fantastic sound quality
- 🎵 Amazing features and sounds
- 💻 Excellent for Gadget integration
- 💡 Versatile for sound design
Room to improve
- 🔌 No AUv3 support
- 🚫 Useless without AUv3
- 💸 Waste of money without AUv3
- 📉 Low output volume
- 🤏 Small controls, difficult manipulation
ButterSynth
From 63 App Store ratingsWhat we love
- ✨ Deep sound design capabilities
- 🎛️ Versatile modulation matrix
- 🔊 Great sound quality
- 💡 Innovative wavetable generator
- 🌟 Serum-like experience
Room to improve
- 📱 Fiddly on small screens
- 🐛 Crashes frequently
- 🐛 Disappears in Cubasis
- 🐛 Spikes CPU usage
- 🐛 Crashes on patch change
Bugs and requests
KORG iMono/Poly
Reported bugs
15 issues- Cannot restore expansion pack
- Cannot find store tab
- Scale selection broken
- User scale does nothing
- MIDI unstable
Show 10 moreShow fewer
- Audio pops
- Monopoly skin removed
- Does not work with nanokey studio Bluetooth
- IAA Panel not displaying host link, transport, record buttons
- MIDI IAA selection not appearing in Cubasis
- On-screen keyboard plays fixed velocity notes
- Arpeggiator doesn't work as expected in Gadget
- User programmed sounds not visible in Gadget
- Patches sound different in Gadget
- App does not take advantage of larger iPhone XS Max screen size
Requested features
42 requests- AUv3 support
- Adaptive Cubasis 3 AUv3
- More iMPC integration
- Transfer patches to desktop VST
- Store preset files on device/flash drive
Show 37 moreShow fewer
- Keyboard portamento to filter cutoff
- Double tap knob to zero/fine adjust
- Save mod wheel position in preset
- Scroll and lock keyboard to key
- Octave switches on left with large keyboard
- Key transpose for arpeggiator
- Undo/redo feature
- Portamento on/off button
- Arpeggio rate as mod destination
- Full-sized keyboard button
- Turn into AUv3
- Bring back Monopoly skin
- Add high-pass filter (HPF)
- MIDI sync in
- Export/share sounds
- Assign right Kaoss pad like left
- AUv3 version
- Latch button for ARP patches
- Random feature
- Double tap to return dials to 0
- Right XY pad assignable
- More extensive external MIDI controller support
- MPE support
- More expansion packs
- Access user patches within Gadget's Montpellier
- Mod destination for VCO Mod Type
- MIDI learn for all controls
- Link on standalone
- Improve effects quality
- Add Korg Prophecy
- Add Trinity, Triton
- Improve IAA panel functionality
- MIDI IAA selection from host
- Fixed velocity on-screen keyboard improvement
- Tempo synchronization with other apps (IAA, MIDI clock, Ableton Link)
- Improve UI for larger screens
- Immaculate skin option
ButterSynth
Reported bugs
39 issues- App crashing with AUM
- Disappears in Cubasis randomly
- Crashes all the time inside Logic
- Changing a patch spikes CPU to 99%
- Crashes on every patch change
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- No audio when rendering or freezing track
- Keyboard doesn't load on iPhone
- iOS18 broke ButterSynth (audio recording issues)
- Failed to load as Auv3
- Crashes as soon as a preset is selected
- Some patches hanging/sounding without input
- CPU spikes to 100% on preset switching
- Audio crackles on preset switching
- Sample module has consistent buzz
- LFOs are extremely simple (no phase offset)
- Square wave LFO is not square (has slew)
- Step sequencer always has glide/slew
- Cannot save custom presets
- No undo function in wave table editor
- AUv3 plugin resets when ButterSynth crashes
- Does not show up as auv3 in Cubasis, AUM, or Audio Evolution
- Crashes regularly even on newest iPad
- Preset changes every time play is pressed
- Not resizing appropriately on smaller screens
- Crashes with unison function in AUM
- White noise on crash with unison
- Sound continues after song stops in GarageBand
- Preset changes on stop, rewind, or play in GarageBand
- Keeps crashing in GarageBand (AUv3)
- Patches in standalone sound different as AUv3
- Crashes when hitting play with arpeggiator/sequencer on iPhone
- No keyboard appears in iPhone standalone mode
- Audio Unit Extension quit error on export
- Lots of crashes in standalone and hosted in AUM
- MIDI not working
- Automation still doesn’t work in Logic Pro
- Random LFO is great for recording sequences
- Preset browser closes each time a new preset is selected
- Works as AUv3 after starting in standalone mode
Requested features
20 requests- MPE popup possible on top of the auv3
- Button to hide built-in keyboard
- Buffer size option
- Additional MIDI mappings (e.g., arpeggiator toggle)
- Sustain pedal support
Show 15 moreShow fewer
- Longer LFO speed for evolving soundscapes
- Alternative skins/color themes
- Pinable preset browser
- Virtual keyboard to remain active while browser is pinned
- Make app take up whole screen (no black borders)
- Master detune
- Parameter lock
- More presets
- Fix square wave LFO to be truly square
- Fix step sequencer glide/slew for discrete steps
- Undo function in wave table editor
- Filter key follow button
- Adjust envelope curves (especially release)
- Easier way to adjust modulation matrix amount
- Phase distortion inclusion
In-app purchases
KORG iMono/Poly
- Expansion Factory Pack$4.99
ButterSynth
No in-app purchases








