Beyond triads and sevenths lie added tones and extensions: the 6ths, add9s and 9th chords that color modern harmony.
An added 9th keeps the triad and drops in the 2nd-an-octave-up; a 6th chord replaces tension with warmth; full 9th chords stack another third on the seventh. Each has a recognizable flavor your ear can isolate the same way it learned major versus minor.
The trainer’s added-note mode plays a chord, then the same chord with one extra note, and asks which note joined: extension hearing reduced to its atom.
Common questions
What is the difference between add9 and a 9th chord?
Add9 is a triad plus the 9th only (0-4-7-14). A true 9th chord also includes the 7th (0-4-7-10-14).