Multidimensional Scaling of Synthetic Musical Timbre: Perception of Spectral and Temporal Characteristics

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Abstract The perceptual correlates of acoustic parameters involved in musical timbre were investigated by examining judgements of timbre dissimilarity. Nine synthetic sounds were created, derived from crossing three levels of spectral and temporal parameters (number of harmonics and rise time, respectively). Two separate conditions were tested, one using single tones, the other using short melodies. Fifteen musically untrained subjects were presented with pairs of stimuli and asked to judge dissimilarity on an 8point scale. The spatial configuration resulting from multidimensional analysis of the data was best fit by a threedimensional model, with the first two dimensions accounting for most of the variance. The perceptual space derived from the analysis indicates that these two orthogonal dimensions corresponded closely to the spectral and temporal differences inherent to the stimuli. Similar results were obtained with both melodies and single tones. A second experiment replicated the findings despite the introduction of random loudness variation, indicating that timbre judgements can be made independently of loudness. We conclude that even musically unselected subjects are sensitive to spectral and temporal information in musical tones, and are able to use them independently in making perceptual judgements of musical timbre.

Resume La perception des parametres acoustiques impliques dans le timbre musical a ete etudiee en examinant les jugements de dissimilarite de timbre. Neuf sons synthetiques ont ete crees, en croisant trois niveaux d'information spectrale (nombre d'harmoniques) et trois niveaux d'information temporelle (temps de montee de l'attaque). Deux conditions, l'une tonale et l'autre melodique, ont ete realisees. Des paires de stimuli ont ete presentees a quinze sujets non-musiciens, qui devaient juger leur degre de dissemblance sur une echelle a 8 points. La configuration spatiale resultant de l'analyse multidimensionnelle des donnees correspondait a un modele a trois dimensions, les deux premieres dimensions expliquant une proportion importante de la variance.

L'espace perceptif obtenu suggere que ces deux dimensions orthogonales correspondaient aux differences spectrales et temporelles de ces stimuli. Des resultats similaires ont ete obtenus avec les sons isoles (condition tonale) et les melodies (condition melodique). Ces resultats, repliques dans le cadre d'une deuxieme experience ou des variations d'intensite (sonie) etaient introduites, suggerent que les jugements de timbre peuvent etre realises independamment de la sonie. L'en-semble de ces donnees indiquent que meme des sujets non-musiciens sont sensibles aux informations spectrales et temporelles des sons musicaux et qu'ils peuvent les utiliser indepen-damment pour percevoir des timbres musicaux.

Musical timbre is an attribute of sound that allows us to distinguish musical instruments when pitch, loudness and duration remain identical. For nearly a century, musical timbre of steady state tones was associated almost exclusively with the spectral energy distribution of a tone, corresponding to the pattern of intensities of the harmonic partials. Studies carried out by Helmholtz (1868) provided experimental evidence to show that this quality of sound depends mainly upon the relative amplitudes of spectral components of complex tones.

However, several lines of evidence suggest that such a definition is too narrow. For instance, it has been shown that the radical changes of the spectrum produced by the distorted output of a transistor radio does not necessarily abolish the recognition of a musical instrument (Eagleson & Eagleson, 1947). Conversely, the timbre of a recorded piano tone is perceived as completely different when it is played backward, even though the original and reversed sound have the same spectra (Berger, 1964). These results indicate that musical timbre does not depend upon a single physical dimension. …