Dissonances is an educational music application which aims to familiarise the audience with sounds traditionally considered as most hostile to our ears. Imagine two tones, of higher and lower pitch. The distance between them is called an interval. Some intervals sound soft and gentle, but there are others which make our ears go numb. The latter include the semitone (the smallest interval on the keyboard; also the distance between adjacent frets on a guitar) and the tritone – known in the Middle Ages as "diabolus in musica". Can such ‘unruly’ sounds be used to create music at all? Check for yourself. You’ll get a semitone and a tritone, visualised as two sticks of different length. You can play with them by arranging them in all possible ways and testing the sound of the various configurations. When you finish playing, it’s also worthwhile to listen to "Musique funèbre" by Witold Lutosławski, who in the 1950s hit on the same idea – to compose music out of semitones and tritones alone.