yml2mid: YAML to MIDI Sequencer

Repository: gitlab.com/lf3/yml2mid
Thesis: UNQ Music Technology Bachelor’s Thesis (2019)

A text-based MIDI sequencer that generates music from YAML files. Developed as part of a Bachelor’s thesis in Music Technology at Universidad Nacional de Quilmes.

What it does

Reads YAML definitions of musical structures and outputs standard MIDI files. The entire composition workflow happens in plain text, version-controlled, and processable by any text tool.

YAML → PyYAML parser → Secuencia (logic) → MIDIUtil → MIDI file

Why plain text for music

Traditional music tools (DAWs, notation software) lock musical information into proprietary formats. They’re not version-controllable, difficult to automate, and couple representation to a specific application.

yml2mid treats musical information as plain text - portable, manipulable, and processable programmatically.

Language structure

Musical discourse organized as a tree:

• Pista (Track) - instrument part
• Sección (Section) - groups of units
• Segmento (Segment) - actual note data
• Articulación - individual notes/events

Property inheritance

Units inherit from parent units using YAML anchors:

base: &base
  transportar: 60
  registro: [0, 2, 4, 5, 7, 9, 11, 12]

a: &a
  <<: *base
  alturas: [5, 5, 6, 5]
  duraciones: [.75, .25, 1, 1]

Registration system

Pitches are indices into a scale array, not absolute MIDI notes:

registro: [0, 2, 4, 5, 7, 9, 11, 12]  # major scale intervals
alturas: [1, 3, 5, 8]                  # C, E, G, C'

Transposition works at two levels: transportar shifts MIDI note, transponer shifts index within scale.

Examples

Feliz Cumpleaños (single track):

• Hierarchical form structure
• Property inheritance across levels
• Transposition within registration
• Lyrics synchronized with notes

Billie Jean (bass, drums, keys):

• Multi-track MIDI output
• Drum programming using fixed registration
• Voice layering for chords
• Different registration per track

Plugin system

User plugins enable algorithmic transformations:

complementos: 'enchufes.py'

unidades:
  a:
    alturas: [5, 5, 6, 5]
    fluctuar:           # calls fluctuar() in enchufes.py
      dinamicas: .5

Allows randomization, variation, generative patterns without modifying core system.

Tech stack

• Python 3 - implementation language
• PyYAML - YAML parsing
• MIDIUtil - MIDI encoding
• Spanish vocabulary - domain-specific language terms

Connection to other work

• UNIX Philosophy paper: Applies same plain-text, composable-process thinking
• COP paper: Structured text as primary reasoning medium
• article-boilerplate: Same documents-as-code philosophy
• National Innovation Award: MIDI controller builds on this thesis work