Journal of New Music Research 0928-2815/98/2704-325$12.00 1998,Vol. 27, No. 4, pp. 325-358 ©Swets & Zeitlinger The Colour of Music: Spectral Characterisation of Musical Sounds Filtered by a Cochlear Model Stefano Baliello 1 , Giovanni De Poli 1 and Renato Nobili 2 1 Dipartimento di Elettronica e Informatica, Università di Padova and 2 Dipartimento di Fisica "G Galilei", Università di Padova ABSTRACT In music research, attention is more and more focused on the main factors of sound perception: This holds in particular for the capability of discriminating music sound features, notably attacks and periodic components, both of which are believed to generate timbre sensation. In this paper it is argued that the fre- quency spectrum of the stationary part of instrument sounds are coded, at some stage, within the nervous system, into a small number of parameters. Somewhat as in vision the light spectrum of a uniformly painted area is coded by the retina into three fundamental colours, the sound parameters seem to represent what may be called "instrument sound colours". The analysis is car- ried out on music sound samples pre-filtered by a non-linear model of the human cochlea. The main reason for this approach lies in the fact that the non-linear filtering performed by the cochlea works to reduce significantly the- information content of acoustic input. Some properties of the model, particu- larly those related to the efficacy of non-linearity in tone masking and noise suppression, are evidenced by examples. The reliability of the model in sound colour characterisation, also in the case of noise-added sounds, is investigated as well. A principal-component analysis of cochlear responses to sounds gener- ated by 21 musical instruments seems to indicate that the spectra of the station- ary parts of instrument sounds are perceived as combinations of three funda- mental components. THE PROBLEM In vision, most of the perceptually relevant features of retinal input are filtered by the primary area of visual brain cortex and thereby separated into specific Sound examples are available in the JNMR Electronic Appendix (EA), which can be found on the WWW at http://www.swets.nl/jnmr/jnmr.html Address correspondence to: G. De Poli, Dipartimento di Elettronica e Informatica, Uni- versità di Padova, Via Gradenigo 6a, 35131 Padova, Italy. E-mail: depoli@dei.unipd.it Manuscript submitted: 8 June 1998.