ON THE EXTERNALIZATION OF SOUND IMAGES

Listeners perceive the sounds of tile real world to be externalized. T he sound images are compact and correctly located in space, The experi ments reported ill this article attempted to determine the characteris tics of signals appearing in the ear canals that are responsible for t he perception of externalization. The experiments used headphones to g ain experimental control, and they employed a psychophysical method wh ereby the measurement of externalization was reduced to discrimination , When the headphone signals were synthesized to best resemble real-wo rld signals (the baseline synthesis) listeners could not distinguish b etween the virtual image created by the headphones and the real source , Externalization was then studied, using both discrimination and list ener rating, by systematically modifying the baseline synthesis. It wa s found that externalization depends an the interaural phases of low-f requency components but not high-frequency components, as defined by a boundary near I kHz, By contrast, interaural level differences in ail frequency ranges appear to be about equally important. Other experime nts showed that externalization requires realistic spectral profiles i n both ears; maintaining only the interaural difference spectrum is in adequate, It was also found that externalization does not depend on di spersion around the head; an optimum interaural time difference proved to be an adequate phase relationship. (C) 1996 Acoustical Society of America.