If we add the note A to our chord, we engineer an extension to our triad, which creates what we describe as a diminished 7th. You will also see that if you add a further minor 3rd, above the note ...

Try to play this interval on a keyboard or piano. A chord is a group of notes ... along with the notation below. A diminished triad is built on the 7th note of the scale. Three are three semitones ...