In the harmonic system used in Western classical music, the smallest difference in pitch normally considered is the semitone, or half-step, anything smaller being regarded as a microtone. A semitone is the interval between the third and fourth notes of an ordinary major scale (from mi to fa in the sol-fa system), and between the seventh and eighth notes as well (from si to do). On an equal-tempered instrument like the piano, a semitone is exactly one-twelfth of an octave, and all other intervals are also exact multiples of the semitone. Other musical traditions, such as those of India, have made use for centuries of notes that fall between the stepping-stones of Western scales. Even in the West, musicians have experimented with microtonal concepts for some time outside the mainstream. A famous example is that of the 16th-century Italian composer and theorist Nicola Vicentino, who constructed a keyboard instrument he called the ‘archicembalo’ with 36 keys per octave. Starting in the late 19th century, some composers embraced microtonal concepts as a fresh means of expression. They began to to develop quasi-harmonic systems, and methods of notation, for handling microtones of various kinds. The development of elecronic tone generation, which allows the use of ‘notes’ of arbitrary frequency, has opened limitless possibilities for further experimentation. Nevertheless, it is also true that to date microtonal music has failed to capture a large listening audience in the West.