Music Box Retro is a precision-crafted virtual music box built with AVAudioEngine bell-tone synthesis, delivering authentic plucked-string timbre for 6 classic melodies. TECHNICAL HIGHLIGHTS - Custom AVAudioSourceNode renders each note as a sine wave with harmonic overtone (12% third harmonic) and exponential amplitude decay — matching the acoustic signature of a real music box - 6 MIDI-encoded melodies: Twinkle Twinkle, Ode to Joy, Brahms Lullaby, Canon in D motif, Fur Elise motif, Sakura - Progressive unlock system: melodies unlock at 3, 8, 15, 25, and 40 total play counts - Playback speed: 0.5x to 2.0x in 0.1x increments - UIFeedbackGenerator haptics synchronized per-note - AppStorage-backed persistence for play count and selected melody - Portrait orientation only - Forced dark color scheme PRIVACY AND DATA Music Box Retro operates entirely on-device. No network requests, no analytics, no crash reporting, no third-party SDKs. Zero data collected or transmitted.