Controlled non-linear distortion effects processing produces a wide range of musically useful outputs, especially in the production of popular guitar sounds. But systematic control of distortion effects has been difficult to attain, due to the complex interaction of input gain, "drive" level, and "tone" controls. Rather than attempting to calibrate the output of commercial effects processing hardware, which typically employs proprietary distortion algorithms, a realtime software-based distortion effects processor was implemented and tested. Three distortion effect types were modeled using both waveshaping and a second order filter to provide more complete control over the parameters typically manipulated in controlling effects for electric guitars. The motivation was to relate perceptual differences between effects processing outputs and the mathematical functions describing the non-linear waveshaping producing variation in distortion. Perceptual calibration entailed the following listening sessions: First, listeners adjusted the tone of each of nine test outputs, then they made both pairwise dissimilarity ratings and attribute ratings for those nine stimuli. The results provide a basis for an effects-processing interface that is perceptually-calibrated for system users.
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