6.6.2 Experiment 2 – Commercial Effects Box

The purpose and methodology of this experiment were similar to the last, except that we used a commercial guitar effects unit rather than numerical clipping. As indicated in Table 6.3, we used a multi-effect box Type ME-30 (BOSS/Roland Corporation, Los Angeles) to produce a set of nine stimuli that had three kinds of effect types (VINT, CRUNCH and HARD) and three drive levels related to the degree of distortion: 50, 70, and 90. The subjects were 20 students who listened to three stimuli at a time to judge their dissimilarity. Thus, the number of stimulus combinations of this experiment was 9C3 = 84 triads. Results achieved were similar to Experiment 1, as shown in Fig. 6.25. The correlation between the scale value for timbral dissimilarity SV and the value of Wφ(0) is 0.92 (p < 0.01).

Fig. 6.25 Results of regression analysis for SV and the mean value of Wφ(0) (Experiment 2)

6.6.3 Concluding Remarks

In these two experiments we found that the main ACF correlate of timbral contrast due to distortion is Wφ(0). This factor is deeply related to the frequency composition of the source signal. In this context, it is interesting that Ohgushi (1980) showed that the lowest and highest frequency components present are the primary determinants of timbre.