I've been looking all over the place for the electronic version of some classical articles on timbre and so far haven't been able to find any of the listed below. I'd be very grateful if anyone could send me the PDFs or even suggest other important works that didn't make the (very short) list.
De Bruijn, A. Timbre-Classification of Complex Tones, Acustica 40 (1978), pp. 108–114.
Letowski, L. Timbre, tone colour, and sound quality: concepts and definitions Archives of Acoustics , 17 , pp.17-30 , 1992.
Preis, A. Timbre of steady-state harmonic complex tones. Acustica , 55 , pp.1-13 , 1984.
Von Bismarck, G. Timbre of steady sounds: A factorial investigation of its verbal attributes Acustica , 30 , pp.146-159 , 1974.
Plomp, R., Steeneken, H.J.M. Effects of phase on the timbre of complex tones. J. Acoust. Soc. Am. , 46 , pp.409-421, 1969.