A Viennese trichord
The A Viennese trichord consists of the A (Perfect unison), Bb (Minor second) and Eb (Diminished fifth) notes.

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