A Viennese trichord
The A Viennese trichord chord consists of the A (Perfect unison), A# (Minor second) and D# (Diminished fifth) notes.

How to play the A Viennese trichord chord
- Find A (Root) on the piano keyboard
- Add A# (Minor second) — 1 semitone above A
- Add D# (Diminished fifth) — 6 semitones above A
- Press all 3 notes simultaneously to sound the A Viennese trichord chord