To study the perceptual structure of musical timbre and the effects of musical training, timbral dissimilarities of synthesized instrument sounds were rated by professional musicians, amateur musicians, and nonmusicians. The data were analyzed with an extended version of the multidimensional scaling algorithm CLASCAL (Winsberg & De Soete, 1993), which estimates the number of latent classes of subjects, the coordinates of each timbre on common Euclidean dimensions, a specificity value of unique attributes for each timbre, and a separate weight for each latent class on each of the common dimensions and the set of specificities. Five latent classes were found for a three-dimensional spatial model with specificities. Common dimensions were quantified psychophysically in terms of log-rise time, spectral centroid, and degree of spectral variation. The results further suggest that musical timbres possess specific attributes not accounted for by these shared perceptual dimensions. Weight patterns indicate that perceptual salience of dimensions and specificities varied across classes. A comparison of class structure with biographical factors associated with degree of musical training and activity was not clearly related to the class structure, though musicians gave more precise and coherent judgments than did non-musicians or amateurs. The model with latent classes and specificities gave a better fit to the data and made the acoustic correlates of the common dimensions more interpretable.

A timbre space represents the mental organization of sound events at equal pitch, loudness, and duration. The geometric distance between two timbres corresponds to their degree of perceived dissimilarity. The dimensions of such a three-dimensional space, established by Krumhansl [l] for a set of 21 synthesized sounds, were investigated with respect to their acoustic characteristics. Several acoustical parameters based on the temporal and frequency properties of the sounds were calculated. The high degree of correlation of several parameters with the perceptual axes lend support to previous interpretations of the qualitative character of two perceptual dimensions and their semantic attributes. The perceptual dimensions "brightness" and "rapidity of attack" tum out to be quantitatively explainable by the center of gravity of the sound spectrum (CGS) and the rise t h e on a logarithmic scale (LTM), respectively. The third dimension, initially called "spectralJEux" corresponds partially to the standard deviation of the timeaveraged harmonic amplitudes from a spectral envelope (IRR). A new verbal descritor, "spectralJine structure" seems to fit better with the results of acoustic analyses.