ABSTRACT
The previous chapter presented a brief exposition of how timbre, pitch, and loudness as the main perceptual attributes of single sounds are derived from periodic vibrations. It may seem that with these attributes we have obtained a reasonably complete picture of how tones are perceived. However, this conclusion would be rather premature. This chapter shows that there are unique auditory processes that are crucially important for dealing with the simultaneous sounds from many sources in our everyday environment. Such sounds may be from competing speakers, musical instruments of an orchestra, cars in the street, and so on. Their vibrations are superimposed in the air and, in order to obtain a reliable impression of what is going on around us, we must be able to distinguish the individual sounds as well as possible. Without appropriate perceptual processing, listeners would find that a speaker became immediately unintelligible as soon as a second speaker joined the conversation, and polyphonic music would be impossible. We might compare this with the difficulty of reading a text from a sheet of paper on which a second text had been written.
