Ear training done properly. SUS4 Ear Pro is the full ear-training course — 172 structured lessons across 20 chapters that take you from identifying simple intervals to recognising complex chord colours and working with frequencies by ear. Musician mode and Sound-Engineer mode are distinct tracks: musicians work through relative pitch, chord quality, and melodic dictation; sound engineers work through Hz identification and frequency matching. The spaced-repetition tutor tracks what you have learned and schedules review at the right time — so the things you are shaky on come back more often, and the things you have nailed do not waste your time. Genuine progress over weeks and months, measurable and persistent. • 172-lesson, 20-chapter structured ear-training course • Musician mode: intervals, chord quality, scales, melodic dictation • Sound-Engineer mode: Hz identification, frequency matching, spectral ear training • Spaced-repetition tutor — reviews what you need when you need it • Progress tracking across every lesson and category • Subscribe monthly, or unlock the full SUS4 suite with one lifetime purchase: the complete 172-lesson, 20-chapter course, both modes, spaced-repetition tutor All audio analysis runs on your device, and the AI tutor uses on-device models where supported. Nothing is sent to a server.