Module: Fet::MusicTheory

Defined in:
lib/fet/music_theory.rb

Overview

Module in charge of handling music theory concepts

Constant Summary collapse

DEGREES =

All 12 degrees

["1", "b2", "2", "b3", "3", "4", "b5", "5", "b6", "6", "b7", "7"].deep_freeze
MAJOR_KEYS =

All 15 keys - 7 sharps…0 accidentals…7 flats.

["C#", "F#", "B", "E", "A", "D", "G", "C", "F", "Bb", "Eb", "Ab", "Db", "Gb", "Cb"].deep_freeze
MINOR_KEYS = 
["A#", "D#", "G#", "C#", "F#", "B", "E", "A", "D", "G", "C", "F", "Bb", "Eb", "Ab"].deep_freeze
MODES_IN_ORDER_OF_DARKNESS = 
[
  ["lydian"],
  ["major", "ionian"],
  ["mixolydian"],
  ["dorian"],
  ["minor", "aeolian"],
  ["phrygian"],
  ["locrian"],
].deep_freeze
DEGREES_OF_MODE = 
{
  ["lydian"] => ["1", "2", "3", "#4", "5", "6", "7"],
  ["major", "ionian"] => ["1", "2", "3", "4", "5", "6", "7"],
  ["mixolydian"] => ["1", "2", "3", "4", "5", "6", "b7"],
  ["dorian"] => ["1", "2", "b3", "4", "5", "6", "b7"],
  ["minor", "aeolian"] => ["1", "2", "b3", "4", "5", "b6", "b7"],
  ["phrygian"] => ["1", "b2", "b3", "4", "5", "b6", "b7"],
  ["locrian"] => ["1", "b2", "b3", "4", "b5", "b6", "b7"],
}.deep_freeze
SEMITONES_FROM_C = 
{
  "C" => 0,
  "D" => 2,
  "E" => 4,
  "F" => 5,
  "G" => 7,
  "A" => 9,
  "B" => 11,
}.deep_freeze
CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS = 
["F", "C", "G", "D", "A", "E", "B"].deep_freeze
CIRCLE_OF_FIFTHS = 
[
  *CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS.map { |note| Note.new(note).flattened_note.flattened_note.flattened_note.full_note },
  *CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS.map { |note| Note.new(note).flattened_note.flattened_note.full_note },
  *CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS.map { |note| Note.new(note).flattened_note.full_note },
  *CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS,
  *CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS.map { |note| Note.new(note).sharpened_note.full_note },
  *CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS.map { |note| Note.new(note).sharpened_note.sharpened_note.full_note },
  *CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS.map { |note| Note.new(note).sharpened_note.sharpened_note.sharpened_note.full_note },
].deep_freeze
ORDERED_NATURAL_NOTES = 
CIRCLE_OF_FIFTHS_WITHOUT_ACCIDENTALS.sort.deep_freeze
SEMITONES_TO_NEXT_NATURAL_NOTE = 
{
  "A" => 2,
  "B" => 1,
  "C" => 2,
  "D" => 2,
  "E" => 1,
  "F" => 2,
  "G" => 2,
}.deep_freeze

Class Method Summary collapse

Class Method Details

.degrees_of_mode(mode_name) ⇒ Object

Raises:



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# File 'lib/fet/music_theory.rb', line 51

def self.degrees_of_mode(mode_name)
  mode_info = DEGREES_OF_MODE.detect { |mode_names, _| mode_names.include?(mode_name) }
  raise InvalidModeName.new(mode_name) if mode_info.nil?

  return mode_info[1]
end

.notes_of_mode(note_name, mode_name) ⇒ Object

A aeolian -> [“A”, “B”, “C”, “D”, “E”, “F”, “G”]

Raises:



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# File 'lib/fet/music_theory.rb', line 81

def self.notes_of_mode(note_name, mode_name)
  relative_major_note_name = relative_major(note_name, mode_name)

  index = CIRCLE_OF_FIFTHS.index(relative_major_note_name)
  result = CIRCLE_OF_FIFTHS[(index - 1)..(index + 5)]
  raise UnsupportedRootName.new(note_name) unless result.size == 7

  result = result.sort
  return result.rotate(result.index(note_name))
end

.relative_major(note_name, mode_name) ⇒ Object

A aeolian -> C

Raises:



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# File 'lib/fet/music_theory.rb', line 93

def self.relative_major(note_name, mode_name)
  note = Note.new(note_name)
  index = CIRCLE_OF_FIFTHS.index(note.full_note)
  raise UnsupportedRootName.new(note_name) if index.nil?

  result_index = index - mode_offset_from_major(mode_name)
  raise UnsupportedRootName.new(note_name) if result_index.negative?

  result = CIRCLE_OF_FIFTHS[index - mode_offset_from_major(mode_name)]
  return result
end

.semitones_from_c(note_name) ⇒ Object

NOTE: returns value from 0 to 11



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# File 'lib/fet/music_theory.rb', line 46

def self.semitones_from_c(note_name)
  note = Note.new(note_name)
  return (SEMITONES_FROM_C[note.natural_note] + note.accidental_to_semitone_offset) % 12
end