AudioKit's AudioKit just pushed a free 1.9 update to King of FM, its FM synthesis app modeled on the Yamaha DX7, DX7 II and TX81Z, and the headline addition is microtonality: 150+ curated alternate scales and the ability to import any custom tuning.
What does microtonality actually unlock?
Every synth defaults to 12-tone equal temperament, the evenly spaced grid that Western pop and dance music runs on. Step outside it and you get access to tunings that predate or ignore that grid entirely: North Indian raga-derived scales, Hexany tunings built from just-intonation ratios, Arabic Egyptian maqam-style modes. For minimal, deep and organic house producers hunting for chords and drones that don't sound like every other rack preset, that's not a gimmick, it's a genuinely different harmonic palette. King of FM 1.9 also reads standard .scl tuning files, the format microtonal composers have used for decades, so anyone can load a historical or invented system on top of the 60-plus world scales already bundled in.
Why does a free app matter here?
Microtonal tools have usually meant expensive hardware synths or specialist plugins aimed at a tiny academic crowd. King of FM ships this for nothing, on hardware most producers already own: an iPhone, an iPad, or an Apple Silicon Mac. It's not a thin emulation either. The app is built on 300-plus presets pulled from over 10,000 multi-sampled tones lifted from the DX7, DX7 II, TX81Z and SY77, including a set of "Holy Grail" DX7 samples that AudioKit says were used on Herbie Hancock sessions. Scale locking now persists across presets, arpeggios, sequences and incoming MIDI, and it runs as both a standalone app and an AUv3 plugin, so it drops straight into an iOS or macOS session next to everything else in the rack.
Who is actually behind it?
AudioKit is the small studio, led by developer Matthew Fecher, behind a run of well-regarded free and low-cost iOS synths since King of FM's 2023 launch. Keeping the flagship instrument free while adding a serious, decades-relevant feature like microtonality is a quieter kind of release than a label drop or a festival booking, but it's exactly the sort of unglamorous tool update that actually changes what a bedroom producer can try on a Tuesday night.
Version 1.9 is a free update for existing users, no in-app purchase required to unlock the new scales.
