# FM4

> Four-operator FM synthesizer for iPad with classic 80s sound. (iPhone/iPad app by Primal Audio I/S.)

- Source: https://appshunter.io/ios/app/fm4/id910545680 (this page in markdown: same URL + `.md`)
- Developer: [Primal Audio I/S](https://appshunter.io/developer/952653514)
- Category: Music, Entertainment
- Price: $6.99
- Rating: 4.63/5 from 19 App Store ratings · 45 written reviews indexed
- Age rating: 4+
- Requires: iOS 8.1 · 62 MB
- Languages: English
- Released: 2014-12-11
- Data updated: 2026-07-29
- Monetization: paid
- User reviews in markdown: https://appshunter.io/ios/app/fm4/id910545680/reviews.md

## What is FM4?

FM4 is a four operator FM synthesizer for iPad. 

  - Reached rank #1 in the app store top paid music category in 32 countries, including United States, Canada, UK, Germany, France, Brazil, Italy, Russia, Australia, and India.

Features:

  - Four operators configurable in eight different routings
  - Three sound engines modelled on 1980s hardware units
  - Eight waveforms derived from classic FM synths
  - 2x, 3x, and 4x polyphonic unison
  - Tempo-syncable arpeggiator with up, down, up-down, and random patterns
  - Microtuning with eight different temperaments
  - Inter-App Audio
  - Supports Audiobus 2
  - MIDI over bluetooth
  - Up to 24 voices of polyphony
  - Presets can be imported/exported through iTunes

Modelled on the popular DX series from the 1980s FM4 provides the same gritty sound, with a modern interface, and without being bound by the limitations of the original units.

Every aspect of the hardware — from envelope curves to sine-table sizes and quantisation errors to digital-to-analogue converters — has been meticulously analysed, in order to recreate the raw and dirty sound of the original units.

The interface has been carefully thought-out and is simple and intuitive, yet powerful — with every parameter being available on a single page. No menus, tabs, or jumping from page to page.

FM4 is capable of producing a multitude of sounds, ranging from punchy basses, crystal-clear bells, and lush pads, to organic textures, striking drums, and piercing leads.

All product names used are trademarks of their respective owners, and reference to these here in no way constitutes an association or affiliation with Primal Audio. All trademarks are solely used to identify the products whose sound was studied during the development of FM4.

## Key features

- Four operators with eight routings
- Three sound engines based on 80s hardware
- Eight classic FM synth waveforms
- Polyphonic unison modes
- Tempo-syncable arpeggiator
- Microtuning with eight temperaments
- Inter-App Audio and Audiobus 2 support

## Recent user reviews (10 of 45)

All indexed reviews: https://appshunter.io/ios/app/fm4/id910545680/reviews.md

### 5/5 — How did I forget …

*2023-01-24, version 1.2.2*

… I had this. Sounds great …

### 4/5 — Will we ever see an update?

*2021-05-03, version 1.2.2*

Tired of being scared every time I update iOS that this synth will finally have to be archived in my frozen (from iOS 13) iPad. Synth is worth getting an iPad for alone so please, do it for us, I’m sure there’s enough of us out there…Either way, thank you for the years of service!

### 5/5 — Sounds amazing.

*2020-10-14, version 1.2.2*

This synth sounds very good. The sounds are not digital in their character. The user interface is well thought out and straightforward. I wish the keyboard width could be changed. I also hope this app will be updated.

### 4/5 — Splendid little 4op FM synth with a great sound

*2019-06-29, version 1.2.2*

Very simple to use and has that rare quality where all the sounds made seem to work well in the mix. Please, please (pretty please) update for AUV3

### 4/5 — It’s okay...

*2018-12-15, version 1.2.2*

Seems like an okay app, but, not remembering the last preset is annoying and no update in 3 years is a worry.

### 4/5 — Awesome 4 OP FM

*2018-03-17, version 1.2.2*

Super easy to use and sounds really GOOD. One of my favs. I’d give it a 4.5 if I could.

Wish list would be:
1.) randomize button (yes, every synth needs one)
2.) MIDI CC control
3.) import TX/DX patches (because I have 1000’s)

My poor old TX81z is sitting in the corner getting dusty since I got FM4.

### 5/5 — You can’t get a TX81Z for $7

*2018-03-03, version 1.2.2*

So get this program, instead.

First the bad:  the envelopes are different, as there is only a single “decay” setting (standard ADSR, vs 2-rate decay with a mid-point level); it’s monotimbral.

Now the good:  The on-screen controls make it feel like a DX synth in an analog synth body, and allows for some great sounds with editing.

The FM synthesis on this is very similar to the TX81Z or DX11, which is an enhanced version (adds non-sine waves) of the 4 operator DX-100/27/21 family.  This thing sounds much better than my old DX-100, but you can switch it into “mode 3” if you miss the noise :-)

Lately I’ve been using this with my Casio CTK (or sometimes Roland Juno DS) to fake a poor man’s Montage:  plug the USB Midi into my iPad Mini, aux cord the iPad audio back into the keyboard, use it to add an FM layer with velocity to a rompler patch.  Sounds pretty darned cool.

It’s a great tool.  It would be nice for them to make a separate upgraded version that works as an AU, so you could embed different patches on different MIDI channels within an iOS DAW.  Someday...

### 4/5 — Great synth, 2 bad it’s not being updated

*2018-02-27, version 1.2.2*

This is a great fm synth, especially if you’re just getting into fm synthesis, unfortunately it appears to be abandoned. The only thing it needs is to be an audio unit, which probably won’t happen. The landscape has changed with Auv3 support and I really use non audio unit less and less so this probably won’t remain on my iPad much longer but it was nice while it lasted

### 5/5 — Fm4 amazing

*2017-08-13, version 1.2.2*

This app is brilliant need i say anymore !!
The sounds its produces and easy the use. Sound design your own patches and samples.

### 5/5 — Fantastic

*2017-07-26, version 1.2.2*

Just bought on the strength of Cuckoo's review. 

Awesome sounds and control. Devs - please keep this alive!

## Frequently asked questions about FM4

### What is FM4?

FM4 is a four-operator FM synthesizer application designed for the iPad. It emulates the sound of classic 1980s FM hardware units while offering a modern and intuitive interface for sound design.

### What are the key features of FM4?

FM4 features four operators with eight routing configurations, three sound engines based on 1980s hardware, eight classic FM synth waveforms, polyphonic unison, a tempo-syncable arpeggiator, and microtuning with eight temperaments. It also supports Inter-App Audio, Audiobus 2, and MIDI over Bluetooth.

### How much does FM4 cost?

FM4 is a paid application. The price is a one-time purchase, and there are no in-app purchases or subscriptions mentioned.

### What kind of sounds can FM4 create?

FM4 is capable of producing a wide array of sounds, including punchy basses, crystal-clear bells, lush pads, organic textures, striking drums, and piercing leads, all with the characteristic gritty sound of vintage FM synthesizers.

### Is FM4 compatible with other music apps?

Yes, FM4 is designed to integrate with other music applications on the iPad. It supports Inter-App Audio and Audiobus 2, allowing it to be used as a sound source or effect within other compatible apps.

## Version history (last 1 release)

### 1.2.2 — 2015-10-01

This app has been updated by Apple to display the Apple Watch app icon.

- Fixed bug in iOS 9 where the operator buttons would disappear.
- Minor bug corrections.

Disclaimer: The are some problems with the locations of popovers in iOS 9.0. We are waiting for Apple to look into this.

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-29.*