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name: adding-scales-chords description: Use when adding new scales, modes, or chord types to MusicTheory - ensures correct interval math, proper categorization, and sharp/flat preferences based on music theory conventions

Adding Scales and Chords

Overview

Scales and chords in this project are defined by their interval structure (semitones from root). Getting intervals wrong breaks the entire musical representation.

Core principle: Verify intervals against authoritative music theory sources before implementing.

When to Use

• Adding a new scale or mode
• Adding a new chord type
• Modifying existing scale/chord intervals
• Creating a new category of scales/chords

Interval System

Intervals are semitones from root note (0-11):

Adding a Scale

Location

client/src/app/services/music-theory.service.ts in the appropriate category within UNIFIED_CATEGORIES

Structure

Copy{
  id: 'scale-name-lowercase',
  name: 'Display Name',
  intervals: [0, 2, 4, 5, 7, 9, 11],  // Semitones from root
  preferSharps: true,                  // Sharp or flat key signature
  type: 'scale' as const
}

preferSharps Rules

Common Scale Intervals

Copy// Diatonic Modes (from major scale)
Ionian:     [0, 2, 4, 5, 7, 9, 11]  // Major
Dorian:     [0, 2, 3, 5, 7, 9, 10]
Phrygian:   [0, 1, 3, 5, 7, 8, 10]
Lydian:     [0, 2, 4, 6, 7, 9, 11]
Mixolydian: [0, 2, 4, 5, 7, 9, 10]
Aeolian:    [0, 2, 3, 5, 7, 8, 10]  // Natural Minor
Locrian:    [0, 1, 3, 5, 6, 8, 10]

// Common Variations
Harmonic Minor:  [0, 2, 3, 5, 7, 8, 11]
Melodic Minor:   [0, 2, 3, 5, 7, 9, 11]
Pentatonic Maj:  [0, 2, 4, 7, 9]
Pentatonic Min:  [0, 3, 5, 7, 10]
Blues:           [0, 3, 5, 6, 7, 10]

Adding a Chord

Location

Same file, chord categories within UNIFIED_CATEGORIES

Structure

Copy{
  id: 'chord-name-lowercase',
  name: 'Display Name',
  intervals: [0, 4, 7],     // Semitones from root
  symbol: 'maj',            // Chord symbol suffix
  preferSharps: true,
  type: 'chord' as const
}

Common Chord Intervals

Copy// Triads
Major:      [0, 4, 7]
Minor:      [0, 3, 7]
Diminished: [0, 3, 6]
Augmented:  [0, 4, 8]
Sus2:       [0, 2, 7]
Sus4:       [0, 5, 7]

// Seventh Chords
Major 7th:      [0, 4, 7, 11]
Dominant 7th:   [0, 4, 7, 10]
Minor 7th:      [0, 3, 7, 10]
Diminished 7th: [0, 3, 6, 9]
Half-Dim 7th:   [0, 3, 6, 10]

// Extended Chords
Major 9th:   [0, 4, 7, 11, 14]  // Note: 14 = 2 + 12 (2nd + octave)
Dominant 9th: [0, 4, 7, 10, 14]

Verification Checklist

Before committing any scale/chord addition:

• Intervals verified against music theory reference (not memory)
• Root note (0) is first in array
• Intervals are in ascending order
• No duplicate intervals
• preferSharps matches convention
• Type discriminator is correct ('scale' or 'chord')
• ID is lowercase with hyphens
• Name is proper display case
• Symbol (for chords) follows standard notation
• Tested by selecting in UI and verifying note display

Common Mistakes

Quick Test

After adding, select the new scale/chord in the UI:

1. Set root to C
2. Verify notes match expected (C major = C D E F G A B)
3. Set root to F# - verify sharps/flats display correctly
4. Play through to hear if it sounds correct