Microtonal music used to demand special hardware or awkward workarounds. MPE changed that. Because every note travels on its own MIDI channel with its own pitch bend, a synth can play notes that sit between the keys of a piano without bending a whole chord out of tune. With controllers such as the new custom-scale system on the Embodme Erae 2 arriving through firmware, it is a good moment to understand how the pieces connect.
The core idea: per-note pitch bend
In classic MIDI, pitch bend affects every note on a channel. Play a chord, bend, and the whole chord moves. MPE assigns each sounding note its own channel, so pitch bend becomes a per-note control. The MPE specification from the MIDI Association builds on this, and it is what lets a controller send, say, a quarter-tone offset to one note while the others stay put.
A microtonal scale is, in practice, a list of offsets from the standard 12-tone grid. When a controller or tuning layer plays degree 5 of a 17-note scale, it picks the nearest MIDI note and adds a pitch bend value to land on the exact frequency.
What a Scala file contains
The Scala software established the widely used .scl file format. It is a plain text file listing the intervals of a scale, either as ratios (such as 3/2) or in cents. A companion .kbm file can map those intervals to keys and set a reference note and frequency. Because it is plain text, you can open a file in any editor, tweak a ratio, and re-import it.
Many modern instruments and controllers can load Scala files directly, which means one tuning file can be shared across a synth, a plugin and a hardware controller. Check each product's documentation, since support for the keyboard mapping file varies.
Pitch bend range: the setting that breaks everything
The single most common microtonal problem is a pitch bend range mismatch. MPE defines a default per-note range of 48 semitones, while the master channel often uses 2. If the controller assumes one range and the synth another, every note will be out of tune by a consistent, confusing amount.
A quick test: play a single note and slide it one octave using your controller's maximum travel. If the synth's pitch lands at a different interval than expected, fix the range on the synth side first. Many plugins list the MPE range in a settings page, and most DAWs let you set it per instrument.
Practical workflow
First, decide where the tuning lives. Either your controller handles the scale and sends notes plus bend values, or the synth applies the tuning internally and the controller just sends notes. Mixing both leads to double-tuning, where offsets are applied twice.
Second, keep chords in mind. Because MPE gives each note its own channel, a controller can retune a chord note by note. This is a major advantage over single-channel microtonal approaches, but it relies on your DAW passing MPE data through unchanged. Confirm that your track is set to MPE mode, and record a short test take to inspect the per-note channels in the piano roll.
Third, save a template. Once pitch bend range, tuning file and MPE zone are set correctly, save the project so you do not have to rediscover the settings.
Where to start
Try a simple 19-tone or 24-tone equal division first, since the maths is easy to hear and verify. Then explore just intonation scales built from ratios, which sound especially striking on sustained, pressure-sensitive sounds. Microtonality and expressive control reward each other: slow glides and subtle vibrato reveal tuning relationships that fixed keys hide.
The tools are cheap, the files are text, and the hardware is increasingly ready. The main investment is patience while you learn what each interval feels like under your fingers.