How to Map 22 Shrutis on MIDI Instruments

Indian classical music relies on a 22-shruti microtonal system, presenting a fundamental challenge when translated to standard MIDI hardware, which is traditionally locked to 12-tone equal temperament (12-TET). To bridge this divide, modern musicians utilize specialized technologies including the MIDI Tuning Standard (MTS), MIDI Polyphonic Expression (MPE), Scala tuning files, and custom algorithmic environments. This article explains the technical workflows and methods artists use to map, trigger, and express these nuanced 22 intervals with precision on modern electronic instruments.

Understanding the 22-Shruti Intonation Problem

Standard MIDI assigns integer values (0–127) to the 12 semitones of Western equal temperament, where each semitone is precisely 100 cents. In contrast, the 22 shrutis of Indian classical music are derived from just intonation (pure mathematical frequency ratios such as 9/8, 5/4, and 3/2) relative to a fundamental drone (Sa). Because shruti intervals deviate from 12-TET pitches by varying microtonal offsets—often between 4 and 22 cents—standard keyboard controllers cannot play them authentically without real-time or system-level pitch intervention.

Method 1: Tuning Files and Custom VST Scaling (.scl and .kbm)

The most direct way to map 22 shrutis to software synthesizers is through the use of Scala files (.scl) paired with keyboard mapping files (.kbm).

  1. Defining the Ratios: The musician builds a 22-tone scale definition using either exact harmonic ratios (e.g., 256/243 for Ekasruti Rishabh) or cent values.
  2. Keyboard Remapping: Because a standard keyboard has only 12 physical keys per octave, a .kbm file determines how these 22 pitches are assigned. Musicians either map an octave across nearly two standard octaves of physical keys (mapping 22 individual keys to the 22 shrutis) or assign only the primary 7 swaras required for a specific raga, tuned dynamically to their correct shruti variants.
  3. Engine Import: Many modern virtual instruments natively support microtonal scaling through file imports or dynamic MTS-ESP integration.

Method 2: MIDI Tuning Standard (MTS) and SysEx Messaging

The MIDI Tuning Standard allows hardware and software instruments to retune individual notes via System Exclusive (SysEx) messages.

Using MTS, an artist can send single-note tuning change messages or bulk scale/octave tuning dumps. This method changes the internal pitch frequency of a target note number at the oscillator level without affecting pitch-wheel data. Software like the ODDSound MTS-ESP suite acts as a master tuning controller in a digital audio workstation (DAW), broadcasting the exact 22-shruti frequency table to all connected plugins simultaneously.

Method 3: MIDI Polyphonic Expression (MPE)

Indian classical music is fundamentally vocal and continuous; microtones are rarely static and are typically approached via ornamentation (gamak) and glides (meend). Standard MIDI channels apply pitch bend globally to all notes on that channel, preventing polyphonic or drone-relative pitch articulation.

MPE solves this by dedicating a separate MIDI channel to every individual note played. Musicians use continuous-surface controllers—such as the ROLI Seaboard, LinnStrument, or Keith McMillen K-Board Pro 4—to achieve the following:

Method 4: Custom DSP Environments (Max/MSP and Pure Data)

For advanced performance setups, musicians build custom routing algorithms using Max/MSP, Pure Data, or scriptable plugins in DAWs like Ableton Live or Reaper.

In these environments: