"Sound is defined as the result of a succession of regular and periodic vibrations. Noise is instead caused by motions that are irregular, as much in time as in intensity. 'A musical sensation,' says Helmholtz 'appears to the ear as a perfectly stable, uniform, and invariable sound.' But the quality of continuity that sound has with respect to noise, which seems instead fragmentary and irregular, is not an element sufficient to make a sharp distinction between sound and noise. We know that the production of sound requires not only that a body vibrate regularly but also that these vibrations persist in the auditory nerve until the following vibration has arrived, so that the periodic vibrations blend to form a continuous musical sound. At least sixteen vibrations per second are needed for this. Now, if I succeed in producing a noise with this speed. I will get a sound made up of the totality of so many noises--or better, noise whose successive repetitions will be sufficiently rapid to give a sensation of continuity like that of sound."