Music Theory Decoder

Master music theory in seconds. 18 in-depth lessons, 20 scales, 30 chords, 12 progressions with playback, plus tuner, metronome & vocal tools. Offline. No subscriptions.

Stop juggling five different apps and theory books. Music Theory Decoder combines a complete music theory guide — 18 in-depth lessons with interactive examples — with the practical tools you actually need: chord finder, scale library, tuner, metronome, drone, and vocal practice.

Built around an interactive Circle of Fifths, every theory concept links directly to the chords, scales, and progressions where you'll use it. Hear it. See it. Understand it.

— WHAT'S INSIDE —

◆ DECODER The interactive Circle of Fifths at the heart of the app. Tap any key to see its diatonic chords (I, IV, V, ii, iii, vi, vii°) laid out clearly. Flip the card to access 12 classic chord progressions — Pop Classic, Four Chords, 50s Doo-Wop, Jazz ii–V–I, 12-Bar Blues, Pachelbel, Andalusian Cadence and more — auto-transposed to your chosen key. Hit play, pick a tempo (60–120 BPM), and hear them with the playing chord highlighted in real time.

◆ SCALES 20 scales across five categories: Modes (Ionian through Locrian), Minor (natural, harmonic, melodic, pentatonic), World (blues, flamenco), Japan (Hirajoshi, Insen, Yo), and Middle East (Phrygian Dominant, Double Harmonic, Hijaz). Every scale shows notes on guitar fretboard and piano keyboard, with audio preview up and down.

◆ CHORDS 30 chord types across all 12 roots — triads, 7ths, 6ths, altered dominants, extended 9/11/13 voicings. Multiple guitar fingerings per chord. Every interval labeled so you understand what you're playing.

◆ INTERACTIVE THEORY GUIDE 18 in-depth lessons covering everything from intervals to extended chords: Intervals, Scales, Three Minor Scales, Circle of Fifths, Chord Construction, Diatonic Chords, Chord Functions, Progressions, Cadences, Voice Leading, Secondary Dominants, Borrowed Chords, Modal Chords, Extended & Altered Chords, Guitar Theory, Piano Theory and more. Each lesson includes interactive staff notation, real examples, and direct links to the Circle of Fifths, scales, and chords where the theory actually lives. Theory you don't just read — you hear and play.

◆ TOOLS (7 professional utilities)

• Tuner — Chromatic, accurate, with smooth spring animations • Metronome — Compound time (6/8, 9/8, 12/8), swing slider, beat accents, tap tempo, four click sounds • Drone — Continuous reference pitch for practice and improvisation. Four waveforms, three octaves • Free Sing — Real-time pitch monitor for singers. See every note you sing with cent-accurate tuning feedback • Vocal Warm-Up — Breathing coach + scale exercises with real-time pitch tracking • Capo Calculator — Instantly find capo position for any key • Transpose — Move any chord progression to any key

— WHY MUSIC THEORY DECODER —

◆ All-in-one. Replace your tuner app, metronome app, theory book, chord library, and vocal tools with one unified experience.

◆ Built for real musicians. Dark theme, bold typography, professional design. Not a cartoon learning app — a working tool.

◆ Vocalists included. Free Sing, Vocal Warm-Up, and Drone form a complete practice suite for singers — a category most theory apps ignore.

◆ Learn by doing. Every theory section links to the interactive Circle of Fifths, scales, and chords. Hear it, see it, understand it.

— WHO IT'S FOR —

Guitarists learning chord theory. Pianists working through modes. Vocalists practicing intonation. Songwriters hunting for the right progression. Students preparing for exams. Band musicians decoding lead sheets on the fly.

Whether you're picking up your first instrument or arranging your next album, Music Theory Decoder gives you the answers fast — and teaches you why they work.

Requires iOS 16.0 or later. Microphone access used only for Tuner, Free Sing, and Vocal Warm-Up — audio is processed on-device and never recorded or transmitted.