Class: HeadMusic::Style::Guides::DiatonicMelody

Inherits:
SpeciesMelody show all
Defined in:
lib/head_music/style/guides/diatonic_melody.rb

Overview

Guidelines for a free diatonic melody (not bound to cantus firmus start/end constraints).

Constant Summary collapse

SINGABLE_INTERVALS =

Modern interpretation: major sixths are singable; sevenths are not.

%w[P1 m2 M2 m3 M3 P4 P5 m6 M6 P8].freeze
RULESET = 
[
  *(MELODIC_CORE - [HeadMusic::Style::Guidelines::SingableIntervals]),
  HeadMusic::Style::Guidelines::SingableIntervals.with(
    ascending: SINGABLE_INTERVALS,
    descending: SINGABLE_INTERVALS
  ),
  HeadMusic::Style::Guidelines::ModerateDirectionChanges,
  HeadMusic::Style::Guidelines::PrepareOctaveLeaps,
  HeadMusic::Style::Guidelines::LargeLeaps.with(
    minimum: :perfect_fourth,
    recovery: %i[consonant_triad any_step repetition opposite_leap_within]
  ),
  HeadMusic::Style::Guidelines::MinimumNotes.with(5),
  HeadMusic::Style::Guidelines::MaximumNotes.with(32)
].freeze
CONTOUR_PEER_WEIGHT_BUDGET =

The non-gate peers of a contour guide share phi^-2 of rubric weight, so that with Contoured at its default weight of phi^-1 (and phi^-1 + phi^-2 = 1), a wrong contour on an otherwise perfect line grades exactly phi^-1.

HeadMusic::GOLDEN_RATIO_INVERSE**2

Class Method Summary collapse

Class Method Details

.contour_ruleset(contour_key, minimum_melodic_intervals: nil) ⇒ Object

Builds a contour guide’s ruleset from this guide’s rules: gate entries pass through unchanged, non-gate peers split the peer weight budget evenly, and the contour guideline is appended at its own default weight. An optional motion gate excludes non-attempts (nil omits it, so a static contour can legitimately repeat a single pitch).



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# File 'lib/head_music/style/guides/diatonic_melody.rb', line 32

def self.contour_ruleset(contour_key, minimum_melodic_intervals: nil)
  gates, peers = RULESET.partition(&:default_gate?)
  peer_weight = CONTOUR_PEER_WEIGHT_BUDGET / peers.length
  motion_gate =
    minimum_melodic_intervals &&
    HeadMusic::Style::Guidelines::MinimumMelodicIntervals.with(minimum_melodic_intervals)
  [
    *gates,
    motion_gate,
    *peers.map { |rule| rule.with(weight: peer_weight) },
    HeadMusic::Style::Guidelines::Contoured.with(contour_key)
  ].compact.freeze
end