Class: HeadMusic::Analysis::Sonority

Inherits:
Object
  • Object
show all
Defined in:
lib/head_music/analysis/sonority.rb

Overview

A Sonority describes a set of pitch class intervalic relationships. For example, a minor triad, or a major-minor seventh chord. The Sonority class is a factory for returning one of its subclasses.

Constant Summary collapse

SONORITIES = 
{
  major_triad: %w[M3 P5],
  minor_triad: %w[m3 P5],
  diminished_triad: %w[m3 d5],
  augmented_triad: %w[M3 A5],
  major_minor_seventh_chord: %w[M3 P5 m7],
  major_major_seventh_chord: %w[M3 P5 M7],
  minor_minor_seventh_chord: %w[m3 P5 m7],
  minor_major_seventh_chord: %w[m3 P5 M7],
  half_diminished_seventh_chord: %w[m3 d5 m7],
  diminished_seventh_chord: %w[m3 d5 d7],
  dominant_ninth_chord: %w[M2 M3 P5 m7],
  dominant_minor_ninth_chord: %w[m2 M3 P5 m7],
  minor_ninth_chord: %w[M2 m3 P5 m7],
  major_ninth_chord: %w[M2 M3 P5 M7],
  six_nine_chord: %w[M2 M3 P5 M6],
  minor_six_nine_chord: %w[M2 m3 P5 M6],
  suspended_four_chord: %w[P4 P5],
  suspended_two_chord: %w[M2 P5],
  quartal_chord: %w[P4 m7]
}.freeze
DEFAULT_ROOT = 
"C4"

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(pitch_collection) ⇒ Sonority

Returns a new instance of Sonority.



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# File 'lib/head_music/analysis/sonority.rb', line 78

def initialize(pitch_collection)
  @pitch_collection = pitch_collection
  identifier
end

Instance Attribute Details

#pitch_collection ⇒ Object (readonly)

Returns the value of attribute pitch_collection.



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# File 'lib/head_music/analysis/sonority.rb', line 68

def pitch_collection
  @pitch_collection
end

Class Method Details

.get(identifier, root: DEFAULT_ROOT, inversion: 0) ⇒ Sonority?

Factory method to get a sonority by identifier Returns a Sonority with pitches starting at the default root (C4)

Parameters:

  • identifier (Symbol, String) —

    the sonority identifier (e.g., :major_triad)

  • root (String) (defaults to: DEFAULT_ROOT) —

    the root pitch (default: “C4”)

  • inversion (Integer) (defaults to: 0) —

    the inversion number (default: 0 for root position)

Returns:

  • (Sonority, nil) —

    the sonority object, or nil if identifier not found



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# File 'lib/head_music/analysis/sonority.rb', line 39

def self.get(identifier, root: DEFAULT_ROOT, inversion: 0)
  identifier = identifier.to_sym
  return nil unless SONORITIES.key?(identifier)

  root_pitch = HeadMusic::Rudiment::Pitch.get(root)
  interval_shorthands = SONORITIES[identifier]

  # Build pitches: root + intervals above root
  pitches = [root_pitch] + interval_shorthands.map do |shorthand|
    interval = HeadMusic::Analysis::DiatonicInterval.get(shorthand)
    interval.above(root_pitch)
  end

  pitch_collection = HeadMusic::Analysis::PitchCollection.new(pitches)

  # Apply inversions if requested
  inversion.times do
    pitch_collection = pitch_collection.invert
  end

  new(pitch_collection)
end

.identifiers ⇒ Array<Symbol>

Returns all available sonority identifiers

Returns:

  • (Array<Symbol>) —

    array of sonority identifiers



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# File 'lib/head_music/analysis/sonority.rb', line 64

def self.identifiers
  SONORITIES.keys
end

Instance Method Details

#==(other) ⇒ Object 



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# File 'lib/head_music/analysis/sonority.rb', line 139

def ==(other)
  other = HeadMusic::Analysis::PitchCollection.new(other) if other.is_a?(Array)
  other = self.class.new(other) if other.is_a?(HeadMusic::Analysis::PitchCollection)
  identifier == other.identifier
end

#consonant? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/head_music/analysis/sonority.rb', line 115

def consonant?
  @consonant ||=
    pitch_collection.reduction_diatonic_intervals.all?(&:consonant?) &&
    root_position.diatonic_intervals_above_bass_pitch.all?(&:consonant?)
end

#diatonic_intervals_above_bass_pitch ⇒ Object 



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# File 'lib/head_music/analysis/sonority.rb', line 132

def diatonic_intervals_above_bass_pitch
  return [] unless identifier

  @diatonic_intervals_above_bass_pitch ||=
    SONORITIES[identifier].map { |shorthand| HeadMusic::Analysis::DiatonicInterval.get(shorthand) }
end

#identifier ⇒ Object 



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# File 'lib/head_music/analysis/sonority.rb', line 83

def identifier
  return @identifier if defined?(@identifier)

  @identifier = SONORITIES.keys.detect do |key|
    inversions.map do |inversion|
      inversion.diatonic_intervals_above_bass_pitch.map(&:shorthand)
    end.include?(SONORITIES[key])
  end
end

#interval_ratio(inversion, &predicate) ⇒ Object (private)

Fraction of an inversion’s diatonic intervals that satisfy the given predicate.



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# File 'lib/head_music/analysis/sonority.rb', line 148

def interval_ratio(inversion, &predicate)
  intervals = inversion.diatonic_intervals
  intervals.count(&predicate).to_f / intervals.length
end

#inversion ⇒ Object 



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# File 'lib/head_music/analysis/sonority.rb', line 93

def inversion
  @inversion ||= inversions.index do |inversion|
    SONORITIES[identifier] == inversion.diatonic_intervals_above_bass_pitch.map(&:shorthand)
  end
end

#inversions ⇒ Object 



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# File 'lib/head_music/analysis/sonority.rb', line 99

def inversions
  @inversions ||= begin
    inversion = reduction
    inversions = []
    inversion.pitches.length.times do |_i|
      inversions << inversion
      inversion = inversion.uninvert
    end
    inversions
  end
end

#quartal? ⇒ Boolean Also known as: quintal?

Returns:

  • (Boolean) 


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# File 'lib/head_music/analysis/sonority.rb', line 125

def quartal?
  @quartal ||= inversions.detect do |inversion|
    interval_ratio(inversion) { |interval| interval.fourth? || interval.fifth? } > 0.5
  end
end

#root_position ⇒ Object 



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# File 'lib/head_music/analysis/sonority.rb', line 111

def root_position
  @root_position ||= inversions[inversion]
end

#secundal? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/head_music/analysis/sonority.rb', line 121

def secundal?
  @secundal ||= inversions.detect { |inversion| interval_ratio(inversion, &:second?) > 0.5 }
end