5 – Microtemporal listening dimensions: Timbre, Harmony and Pitch height73Risset and Wessel concluded that the attack transients constitute an impor-
tant part of instrument tones. If the attack segment of a tone is removed in
a tape recording, the instrument is no longer recognizable.
Many tones like those produced by the piano or percussion instruments
are characterized mainly by the complex temporal evolution of their tran-
sients, as they have no steady state at all. Transients are intrinsically
complex, and they are not reproducible from one tone to another. Houtsma
(1989) points out that high and low tones from an instrument normally
have different spectra; a low piano tone typically contains little energy at
the fundamental frequency and has most of its energy at higher partials,
while a high piano tone typically has a strong fundamental and weaker
higher partials.
The multidimensional nature of timbre has been investigated by Carol
Krumhansl (1989). With David Wessel, she conducted an experimental study
of the similarities and dissimilarities of 21 timbres synthesized by means a
frequency modulation technique. Most of the timbres were designed to
simulate traditional instruments such as horn, trombone, trumpet, oboe,
clarinet, bowed string, guitar, harpsichord and piano. A few others were
synthetic hybrid timbres such as "guitarnet", a hybrid of guitar and clarinet,
and "striano", a hybrid of strings and piano. A group of musically trained
listeners were asked to judge the relative similarities of these timbres, and the
obtained data were treated by a multidimensional scaling technique.
As a result of this study, three common dimensions of timbre were
found. The first dimension corresponds to the rapidity of attack, reflecting
differences for example between the sharp attack of plucked instruments
like harpsichord and guitar and the comparatively slow attack of horns or
bowed strings.
The second dimension corresponds to brightness, depending upon the
distribution of power in the sound spectrum. In relatively bright instru-
ments like the oboe and trumpet, energy is concentrated in the higher
components, while instruments such as horns and trombones are charac-
terized by energy concentration in the lower components.
The third dimension, named spectral flux, corresponds to the temporal
evolution of spectral components, reflecting differences for example
between woodwind and brass-like timbres, the latter characterized by
spectral contents changing with amplitude.
In addition, some timbres were found to possess specific qualities that
are not explained by these three dimensions, such as the clarinet timbre
which is unique in its absence of even harmonics.
The dimensions proposed by Krumhansl have been confirmed by later
acoustic analyses. Donnadieu et al. (1994) conclude that attack quality is
highly correlated with the logarithm of attack time, and brightness is highly
correlated with the spectral center of gravity. The third dimension, under-
stood as spectral fine structure, is well correlated with the ratio between the
amplitudes of even and odd harmonics.ng.