MIDI to Solfège Input Specification

Purpose and scope

This specification defines a single transformation contract: a stream of MIDI events is consumed, and a Solfège Output object is emitted. The spec is concerned only with what that output object looks like and what triggers its emission. It is not concerned with which physical instrument produced the MIDI stream, how chords or gestures are interpreted, how diacritics are encoded in MIDI terms, or what the receiving application does with the output.

Those concerns belong to the mapping layer described in MIDI to Solfège Mapping. The strict separation between this spec and the mapping layer is intentional: the output type defined here is stable and instrument-agnostic. Mappings are creative, instrument- specific, and user-configurable. Multiple mappings can target this same spec.

Output type

A single Solfège Output object has the following structure:

{
  solfege: SolfegeSyllable,
  commas: Array<CommaString>
}

Where:

SolfegeSyllable = "Do" | "Ra" | "Re" | "Me" | "Mi" | "Fa"
               | "Fi" | "So" | "Le" | "La" | "Te" | "Ti"

CommaString = string // Format: "±x/y"

SolfegeSyllable

The twelve syllables of Uniform Solfège, representing the twelve solfège syllables of the chromatic period. They are an enumeration — a closed, ordered set of labels. They do not encode absolute pitch, register, or octave. Those are application-layer concerns.

The syllables in chromatic order:

Syllable	Chromatic position
Do	0
Ra	1
Re	2
Me	3
Mi	4
Fa	5
Fi	6
So	7
Le	8
La	9
Te	10
Ti	11

CommaString

A single comma entry specifies a navigational path step formatted as a string ±x/y, where x is the integer step magnitude and y is the prime family divisor.

x (magnitude and direction):
- A positive step compresses the subperiod — the equivalent of a sharper deviation in pitch terms, or a shorter duration in rhythmic terms.
- A negative step expands the subperiod — the equivalent of a flatter deviation in pitch terms, or a longer duration in rhythmic terms.
y (prime family):
- The valid prime families recognised by PPT up to the 11-limit are: Du, Tri, Qui, Sep, Undec.

Note on Du interpretation: A Du entry (y=Du) is interpreted as a coarsest-frame edge (licensed pivot) when it is the first digit relative to the currently-open anchor frame (before any narrower subdivision has been chosen). It is interpreted as an ordinary interior bisection otherwise. This distinction is crucial for parser validation of Transient Excursions.

The commas array

The commas array is an ordered sequence. Order is meaningful. Each entry in the array represents one navigational step through the prime lattice, taken in sequence from the solfège anchor. The position described by a commas array is the result of applying each comma entry in order, not the sum of their magnitudes.

Order significance is required because Du fractal navigation is inherently path-dependent: each Du step specifies which half of the current subperiod to enter, and the sequence of those decisions is what locates a position in the subdivision tree. The same requirement is extended to all prime families for consistency and to permit mixed-prime fractal navigation in future use.

An empty commas array is valid and common. It indicates the solfège syllable at its unmodified 12TET anchor position.

COMMIT

COMMIT is the signal that causes a Solfège Output object to be emitted. It is always an explicit MIDI event — never implicit, never inferred from silence, note release, or decay. What MIDI event constitutes COMMIT is determined by the mapping layer, not by this spec.

This spec requires only that:

COMMIT is a designated, explicit MIDI event.
All MIDI events received since the previous COMMIT belong to the current bundle — the unit of input that resolves to one Solfège Output object.
COMMIT causes the current bundle to be evaluated and one output object to be emitted, then the bundle resets.
A COMMIT with an empty bundle is a no-op.

Bundle

A bundle is the set of MIDI events accumulated between two COMMIT signals. It has no minimum size beyond being non-empty at the time of COMMIT. A bundle containing a single note-on event is valid. A bundle containing many note-on events with pitch bend data and continuous controller messages is equally valid.

This spec does not define how a bundle is interpreted — that is the mapping layer’s responsibility. The spec only defines that the bundle is the unit of evaluation and that its result is one Solfège Output object.

What this spec does not define

The following are explicitly out of scope and belong to the mapping layer or the receiving application:

Which MIDI note numbers correspond to which SolfegeSyllables
How chords (multiple simultaneous note-on events) are resolved to a single syllable
How pitch bend data is resolved to Comma values
How continuous controller data is interpreted
What COMMIT looks like as a physical gesture on any instrument
Register, octave, and coil-layer assignment
Half-size glyph status
Layer assignment (pitch layer, rhythmic layer, register layer)
Temperament and tuning system application
Enharmonic equivalence decisions

Relationship to Prime Period Diacritics

The comma system defined in this spec is the abstract mathematical layer of which Prime Period Diacritics (PPD) is the writing system rendering. PPD glyph forms encode specific comma values as visual marks on a solfège character. The output object here carries the same information in a form that is readable by software rather than by eye.

See Prime Period Diacritics — Overview and Prime Lattice for the mathematical relationship between comma values and their written representations.