- check isDrumIndex
  - use as factor in determining if it's a drum channel (might not be)

- within an instrument:
  - check program against general midi if not null
    - use as factor in determining kind of instrument

- determine if the notes in this instrument/channel are part of a chord progression with notes on other channels, or if they should be considered a monophonic melody.




file {
  tempo, (constant)
  time_signature, (constant)
  path,
  tracks: [array of { name: str }],
  channels: [
    {
      index: 0, // which midi channel? (0-15)
      isDrumIndex: boolean (is this one maybe a drum channel?)

      // one instrument is active at each point in time on the channel.
      instruments: [
        {
          program: general midi index or null,
          notes: []
        }
      ]
    }
  ]
}





Result: array of arrays of notes which all meet the description "monophonic melody"



Sam's plan:

1. based on directly expressed top-level ideas like general midi program, isDrumIndex, score for likelihood of being a monophonic melody
2. segment instrument contents into sub-arrays based on:
  - characteristics of note length distribution
  - characteristics of pitch distribution
  - characteristics of velocity distribution

3. check for basic stuff like % of notes starting simultaneously with other notes in the same instrument
  - If above ~5%, low score for monophonic melody.
    - within one instrument, simultaneously-starting notes in a monophonic melody should be very rare, only occurring as a result of accidents or very occasional diads/triads
4. check again for % of notes starting simultaneously with other notes in the same file, but not in the same instrument
  - If below ~80%, high score for monophonic melody
    (reason being that chords spread across multiple instruments/channels will probably have very high correlation here, but a monophopnic melody will probably only have "kind of high" correlation here)
5. if score exceeds a threshold, consider that entire instrument to be a monophonic melody.