A M/ODEL TO ADD EXPRESSIVENESS TO AUTOM/lATIC MLIUSICAL
PE RFO RMlA NC E
Canazza Sergio, De Poli Giovanni, Di Sanzo GiaLnni, Vidolin, Alvise
Dipartimento di Elettronica e Informatica - Universitjt di Padova
via Gradenigo 6a - 35100 Padova - Italy
canazzaedei.unipd.it; depoli edei.unipd.it; vidolinedei.unipd.it.
ABSTRACT
The fact that music can be used as a means for expression and communication is often acknowledged. Yet this is
one of the least understood aspects of music, at least as far as scientific explanation goes. The performer introduces
some deviations from nominal values specified in the score, that characterizes his own performance. It is known that
several performances of the same score often differ significantly, depending on performer's expressive intentions.
A model of expressiveness has been developed on the base of results of acoustic and perceptual analyses. The
model allows to obtain different performances, by modifying the acoustic parameters of a given neutral performance.
The modification of the input performance is performed by algorithms which use the hierarchical segmentation of the
musical structure. Opportune envelope curves are applied, for every hierarchical level, to the principal acoustic
parameters. Level's self-similarity is the main criteria for the envelope curves construction. The modular structure of
the system defines an open architecture, where the rendering steps can be realized both with synthesis and postprocessing techniques. Different synthesis techniques, like FM, physical models or wavetable have been explored.
1. INTRODUCTION
Music is an important means of communication where three actors participate: the composer, the performer and the
listener. The composer instills into his works his own emotions, feelings, sensations and the performer communicates
them to the listeners. The performer uses his own musical experience and culture in order to get from the score a
performance that may convey the compositor's intention.
Different musicians, even when referring to the same score, can produce very different performances. The score
carries information such as the rhythmical and melodic structure of a certain piece, but there is not yet a notation able
to describe precisely the temporal and timbre characteristics of the sound. The conventional score is quite inadequate
to describe the complexity of a musical performance so that a computer might be able to perform it. Whenever the
information of a score (essentially note pitch and duration) is stored in a computer, the performance sounds mechanic
and not very pleasant. The performer, in fact, introduces some micro-deviations in the timing of performance, in the
dynamics, in the timbre, following a procedure that is correlated to his own experience and common in the
instrumental practice. It is exactly for this great variety in the performance of a piece that it is difficult to determine a
general system of rules for the execution (Kendall Carterette 1990). An important step in this direction was made by
Sundberg and co-workers (Friberg 1991) They determined a group of criteria which, once applied to the generic
score, can bring to a musically correct performance. Further on, the performer operates on the microstructure of the
musical piece not only to convey the structure of the text written by the composer, but also to communicate his own
feeling or expressive intention. Quite a lot of studies have been carried on in order to understand how much the
performer' s intentions are perceived by the listener, that is to say how far they share a common code (Seashore 1937;
Sloboda 1983, 1985; Canazza et al. 1997a). Gabrielsson (1995, 1997) and Gabrielsson & Juslin (1996) in particular,
studied the importance of emotions in the musical message. In this context, we tried to understand the way an
expressive intention can be communicate to the listener and we realized a model able to explain how it can be
possible to modify the performance of a musical piece in such a way that it may convey a certain expressive
intention. A group of sensorial adjectives was chosen (haLrd, soft, light, heavy, bright, dark ) which should inspire a
certain expressive idea to a musician. We observed that a musician, inspired by appropriate adjectives, produces
different performances of the same piece. Perceptual analysis (Canazza et al. 1997a) proved that the audience can
indeed perceive the kind of intention he wanted to convey. Acoustic analysis (Canazza et al. 1997b, 1997c)
confirmed that there are micro-deviations in the note parameters. We outlined models to connect such deviations with
the intention wanted. Following the analysis-by- synthesi s method, some musical synthesis were produced to verify
and develop a model of musical expressiveness (Canazza et al. 1997c).
This paper, starting from the results of the acoustic and perceptual analysis, presents the design of a model able to
add expressiveness to automatic musical performance.
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