A diminished seventh chord is a four-note chord, which consists of four notes: the root, the minor third, the diminished fifth, and the diminished seventh.
The formula 1-b3-b5-bb7 represents the intervallic structure of a diminished seventh chord:
For example, in a C diminished seventh chord:
The combination of these four notes (C, Eb, Gb, Bbb) creates the sound of a C diminished seventh chord.
Diminished seventh chords have a dissonant and tense quality due to the presence of diminished intervals. They are often used for creating tension and leading to resolutions in music, making them a common choice in jazz and classical compositions.
On a piano or keyboard, diminished seventh chords are typically played by pressing the root note, the minor third, the diminished fifth, and the diminished seventh.
In guitar playing, diminished seventh chords are formed by pressing down specific combinations of strings and frets, following chord diagrams or finger positions.