Communication Acoustics: An Introduction to Speech, Audio and Psychoacoustics

9 Basic Function of Hearing

This chapter starts by discussing the most fundamental of questions regarding an auditory object: under what conditions does it exist? Two physical attributes limit the audibility of a frequency component of sound: the sound pressure level (SPL) and frequency. If the SPL is too low, nothing is heard. If it is too high, the sensation of sound is accompanied by the sensation of pain, and beyond some limit in the SPL the ears are destroyed. The threshold of pain is commonly taken as the upper limit of the SPL to generate auditory events in sound and voice techniques. On the other hand, sound components with too low frequencies are not perceived as sound, but more as a sensation of vibration, and sound components with too high frequency content are not perceived at all. The attributes also interact with tonal signals; the SPL threshold of audibility depends in a complicated manner on frequency. The first section in this chapter will discuss these issues.

When multiple sounds are presented to the subject, they influence each other's audibility. In spectral masking, sounds in different frequency regions make each other inaudible, and in temporal masking, the same happens in the temporal dimension. The basics of masking are discussed in the second and third sections of this chapter.

The last section in this chapter discusses the first steps of spectral analysis conducted in hearing; that is, the characteristics of the frequency bands in hearing. The processing ...