This screen explains the acoustical and mathematical background to musical intervals. It also provides a practical demonstration of the scale of C major on a piano keyboard, with all the names for the intervals in this scale, arranged in a chart below the keyboard. Clicking the mouse over any key will play that note. You can also type the note names C, , E, F, G, A, B on the computer keyboard to hear the corresponding notes played.
At the foot of the screen, there is a button for playing the C scale and another for the C triad. You will hear the notes and see the piano keys depressed as the scale or triad is played.