THE IMPORTANCE OF THE HIGH FREQUENCIES OF CLARITY INDEX FOR THE PERCEPTION OF MUSICAL CLARITY

The purpose of the present study was to analyse the relative importance of the different frequency ranges of C80 for the prediction of musical clarity. This task was accomplished by means of a listening test in which 24 subjects with normal hearing and musical background rated stimuli in terms of musical clarity. Two different sets of stimuli were rated: one set was composed of SRIRs that were computationally modified to attain specific values of C80 in individual pairs of octave bands, while the other set was composed of SRIRs obtained from seven different concert halls. The ratings of clarity obtained for the first set of stimuli were regressed with the average C80 values of pairs of octave bands of their SRIRs. The obtained regression model can be used to predict a rating of musical clarity on a scale from 0 to 100 from an arbitrary RIR. The model was tested by comparing the predicted ratings when evaluating the regression formula with the octave band values of C80 of the seven halls, with the mean values of the ratings of clarity of these halls. It was found that the average error in the predictions of regression model relative to the actual ratings was approximately 10.5 scale points. A correlation analysis was conducted between the ratings of clarity of the seven halls and their octave band values of C80. It was found that the average of the 4000 and 8000 Hz octave band values of C80 had the highest correlation with musical clarity (rs = 0.71), while the correlation between clarity and the C80(3) metric proposed by Beranek was not particularly high (rs = 0.46). The present study has helped in elucidating the relative importance of the different frequency ranges of C80 in the perception of musical clarity. In the past, several averaging schemes of the octave-band values of C80, which were believed to be highly correlated with clarity, have been proposed. However, these SVFA measures of C80 originated in the practical experience of acoustical consultants and the literature is limited in this area. Both the obtained regression model and the results of the correlation analysis presented in 9.3, indicate that the high frequencies of C80 are very important for the perception of musical clarity. By using these results, the concert hall designer has an improved method to predict the impact that a change of C80, due to the modification of the geometry or the materials of the hall, will have in perceived clarity.