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

{
  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

// 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

{
  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

// 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