There is, in fact, a fourth dimension to sound: phase, which characterises how much the various simple sounds which make up a complex sound like speech are in step with each other. Phase is usually taken as being irrelevant in speech. In perception studies, however, it is important. Detection of phase is one of the ways in which we are able to decide the direction from which a sound is coming toward us. Because of the difference in arrival time of a sound at our two separate ears we are able to compute the direction of the sound from the degree to which the two different signals (one from each ear) are out of phase (i.e. out of step with one another). It is, among other things, artificial manipulation of this parameter which makes stereophonic or binaural sound reproduction possible.…
