When we hear a musical sound, we have no difficulty in recognizing the kind of instrument that produces it. The sound of the violin, of the piano, of the cornet, has each its own peculiarity.
One voice is full and rich, another is thin, and another is monotonous. The characteristics which enable us to assign a sound to its source are called the quality of the tone. The physical explanation of quality is that most sounding bodies vibrate not only as a whole, but also in various parts, as does the string of a piano, and that a sound is rich in quality when it contains various overtones pro duced by these partial vibrations, as well as the fundamental tone of the vibrating body.
The wave form of a tone which is rich in quality is a complex one. Besides the full-length wave given by the fundamental tone, there is one 1/2 as long, given by the first harmonic, one 1/3 as long, given by the second harmonic, and so on. For example: If the fundamental is c', the first harmonic is c", the second is g", the third is c'", etc.
