ABSTRACT
This chapter explains timbre which is considered in terms of the acoustics of sounds that have different timbres and the psychoacoustics of how sounds are perceived. It concerns sounds that in some sense could be said to "deceive" the ear. Most listeners report hearing a high tone in the right ear alternating with a low tone in the left ear as illustrated in the figure, no matter which way round the headphones are placed. A musical illusion only works by virtue of establishing a strong expectation in the mind's ear of the listener. "Steady state" does not mean that no aspect of the note varies. A note from any acoustic musical instrument typically changes dynamically throughout in its pitch, loudness and timbre. A pitch illusion, which has been compared with the continuous staircase pictures of M. C. Escher, has been demonstrated by Shepard and is often referred to as a "Shepard tone".
