Class: HeadMusic::Style::Guides::SpeciesHarmony

Inherits:
Base
  • Object
show all
Defined in:
lib/head_music/style/guides/species_harmony.rb

Overview

Base class for species harmony guides. Inherits analysis behavior from Base; exists as a semantic marker distinguishing harmony guides from melody guides.

Constant Summary collapse

HARMONIC_GATES =

A companion voice, without which the harmonic guidelines reach for a cantus firmus that is not there and raise; and three notes, without which a voice against an empty companion grades as though it were fine.

The gate asks whether there is anything to judge, not whether the density is right. Splatted by each subclass, for the reason MELODIC_GATES gives.

[
  HeadMusic::Style::Guidelines::SetAgainstAnotherVoice,
  HeadMusic::Style::Guidelines::MinimumNotes.with(3)
].freeze
HARMONIC_CORE = 
[
  HeadMusic::Style::Guidelines::ApproachPerfectionContrarily,
  HeadMusic::Style::Guidelines::AvoidCrossingVoices,
  HeadMusic::Style::Guidelines::AvoidOverlappingVoices,
  HeadMusic::Style::Guidelines::ConsonantDownbeats,
  HeadMusic::Style::Guidelines::NoParallelPerfectOnDownbeats,
  HeadMusic::Style::Guidelines::PreferContraryMotion,
  HeadMusic::Style::Guidelines::PreferImperfect
].freeze
DIMINUTION_HARMONIC_CORE =

For the diminution species, which set several counterpoint notes against each whole note of the cantus firmus.

[
  HeadMusic::Style::Guidelines::NoParallelPerfectAcrossBarline,
  HeadMusic::Style::Guidelines::NoStrongBeatUnisons
].freeze
DIMINUTION_HARMONIC_CRAFT =

What a diminution species inherits: both cores, splatted into one secondary_items call so that adding to either reaches all four guides.

[*HARMONIC_CORE, *DIMINUTION_HARMONIC_CORE].freeze
INHERITED_HARMONIC_CRAFT =

The tier policy, not a mechanism: every harmony guide declares its own tiers outright, and this list is what base_spec holds them to – no member of it may sit in a guide’s primary tier, because a species guide is about the dissonance treatment its rhythm makes possible and two-part craft is background.

Wider than either splat by one. NoParallelPerfectWithSyncopation is declared by hand in the only two guides that want it, so it is in no core constant, but it is the same prohibition as the other three specialized for syncopation: primary it would take phi^-1 of fourth and fifth species by itself.

A deliberate promotion is not written here – removing a member would relax the policy for all seven guides – but in HARMONIC_CRAFT_PROMOTIONS below, which names the exception and the one guide it applies to.

[
  *DIMINUTION_HARMONIC_CRAFT,
  HeadMusic::Style::Guidelines::NoParallelPerfectWithSyncopation
].freeze
HARMONIC_CRAFT_PROMOTIONS =

The named exceptions to the policy above: guide key => the inherited items that guide weighs as taught rules. Every promotion is written down once here, so that a tier declaration in a guide can be read as a decision rather than as an oversight, and so that base_spec can hold the other guides to the policy without hard-coding which one departs from it.

NoParallelPerfectOnDownbeats is primary in first species alone. First species has no dissonance treatment to be about – its other two primaries are rhythm-and-texture bookkeeping – so note-against-note consonance handling is what the species teaches. In the six guides that do teach a dissonance treatment, promoting it would weigh the prohibition as heavily as the treatment the guide exists for, and would raise the grade of a submission already failing that treatment by halving the weight it forgoes.

Keyed by key string rather than class constant: head_music.rb loads this file before the guides that subclass it, so a class reference here is a load-time NameError.

{
  "first_species_harmony" => [HeadMusic::Style::Guidelines::NoParallelPerfectOnDownbeats]
}.freeze

Class Method Summary collapse

Class Method Details

.category ⇒ Object 



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# File 'lib/head_music/style/guides/species_harmony.rb', line 80

def self.category
  :harmony
end