Multidimensional perceptual scaling analyses were performed for a set of stimuli that were generated by submitting two pre-recorded guitar performances to a popular effects processor designed to model a variety of guitar amplifiers. Within three characteristic types of amplifier distortion (British Crunch, Combo 335, and Twin Drive), the tone color of the output was varied using three nominal output character settings (Normal, Edge, and Punch). As it was only the variation in timbre and tone coloration that was of interest, the loudness of the processor outputs was equalized prior to listening sessions in order to determine the most salient perceptual attributes of these amplifier models as their output character was varied. This analysis separated out two salient tone-coloration dimensions from a third dimension of timbral variation. This third dimension corresponded to a timbral characteristic particular to the three modeled amplifier types. Interpretation of the meanings of the three dimensions was aided by the results of a semantic differential analysis for the same sounds using bipolar adjective scales. The timbral quality distinguishing the three modeled amplifiers was well described by the verbal attributes "wildness" and "hardness." The tone coloration variation introduced particularly by the Punch output character settings was most highly correlated with ratings on "thickness" and "heaviness" scales. A straightforward relation was also found for the use of the "sharpness" and "muddiness" scales in describing tone coloration variation introduced by the Edge output character setting, though interpretation was complicated somewhat by the correlation of these ratings with the timbral quality that differed between the amplifiers. The results of this study provided the basis for a graphical user interface to computer-controlled musical effects processing that is more immediately accessible to a wide range of users.
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