Sound Vibrations, Pure Tones, and the Perception of Pitch

Abstract

We hear a “sound” when the eardrum is set into a characteristic type of periodic motion called vibration. This vibration is caused by small pressure oscillations of the air in the auditory canal associated to an incoming sound wave. In this chapter we shall first discuss the fundamentals of vibratory motion in general and then focus on the effects of eardrum vibrations on our sensation of hearing. We shall not worry at this stage about how the eardrum is set into motion. To that effect, let us imagine that we put on headphones and listen to tones generated therein. In the lower frequency range the eardrums will follow very closely the vibrations of the headphone diaphragms. This approach of introducing the subject is somewhat unorthodox. But it will enable us to plunge straight into the study of some of the key concepts associated with sound vibration and sound perception without spending first a long time on sound waves and sound generation. From the practical point of view, this approach has one drawback: the experiments that we shall present and analyze in this chapter necessarily require electronic generation of sound rather than natural production with real musical instruments. Whenever possible, however, we shall indicate how a given experiment could be performed with real instruments.