Class: Musa::Transcriptors::FromGDV::ToMIDI::Turn

Inherits:
Musa::Transcription::FeatureTranscriptor show all
Defined in:
lib/musa-dsl/transcription/from-gdv-to-midi.rb

Overview

Turn transcriptor for MIDI playback.

Expands turn ornaments into a four-note figure that circles around the main note. A turn is a melodic embellishment consisting of the note above, the principal note, the note below, and the principal note again.

Turn Types

  • .turn or .turn(:up) - Start with upper neighbor (upper, main, lower, main)
  • .turn(:down) or .turn(:low) - Start with lower neighbor (lower, main, upper, main)

Processing

Given .turn on a note:

{ grade: 0, duration: 1r, turn: true }

Expands to four equal notes:

[
  { grade: 1, duration: 1/4r },    # Upper neighbor
  { grade: 0, duration: 1/4r },    # Main note
  { grade: -1, duration: 1/4r },   # Lower neighbor
  { grade: 0, duration: 1/4r }     # Main note
]

Each note gets 1/4 of the original duration.

Process: .turn

Examples:

Upper turn

turn = Turn.new
gdv = { grade: 0, duration: 1r, turn: true }
result = turn.transcript(gdv, base_duration: 1/4r, tick_duration: 1/96r)
# => [
#   { grade: 1, duration: 1/4r },   # +1
#   { grade: 0, duration: 1/4r },   # 0
#   { grade: -1, duration: 1/4r },  # -1
#   { grade: 0, duration: 1/4r }    # 0
# ]

Lower turn

gdv = { grade: 0, duration: 1r, turn: :down }
turn.transcript(gdv, base_duration: 1/4r, tick_duration: 1/96r)
# => [
#   { grade: -1, duration: 1/4r },  # -1
#   { grade: 0, duration: 1/4r },   # 0
#   { grade: 1, duration: 1/4r },   # +1
#   { grade: 0, duration: 1/4r }    # 0
# ]

Instance Method Summary collapse

Instance Method Details

#transcript(gdv, base_duration:, tick_duration:) ⇒ Array<Hash>, Hash

Transcribes turn to four-note sequence.

Parameters:

  • gdv (Hash) —

    GDV event possibly containing :turn

  • base_duration (Rational) —

    base duration unit

  • tick_duration (Rational) —

    minimum tick duration

Returns:

  • (Array<Hash>, Hash) —

    array with turn notes, or unchanged event



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# File 'lib/musa-dsl/transcription/from-gdv-to-midi.rb', line 361

def transcript(gdv, base_duration:, tick_duration:)
  turn = gdv.delete :turn

  if turn
    start = :up

    check(turn) do |turn|
      case turn
      when true, :up
        start = :up
      when :down, :low
        start = :down
      end
    end

    duration = gdv[:duration] / 4r

    gdvs = []

    case start
    when :up
      gdvs << gdv.clone.tap { |gdv| gdv[:grade] += 1; gdv[:duration] = duration }
      gdvs << gdv.clone.tap { |gdv| gdv[:grade] += 0; gdv[:duration] = duration }
      gdvs << gdv.clone.tap { |gdv| gdv[:grade] += -1; gdv[:duration] = duration }
      gdvs << gdv.clone.tap { |gdv| gdv[:grade] += 0; gdv[:duration] = duration }
    when :down
      gdvs << gdv.clone.tap { |gdv| gdv[:grade] += -1; gdv[:duration] = duration }
      gdvs << gdv.clone.tap { |gdv| gdv[:grade] += 0; gdv[:duration] = duration }
      gdvs << gdv.clone.tap { |gdv| gdv[:grade] += 1; gdv[:duration] = duration }
      gdvs << gdv.clone.tap { |gdv| gdv[:grade] += 0; gdv[:duration] = duration }
    end

    super gdvs, base_duration: base_duration, tick_duration: tick_duration
  else
    super
  end
end