| Résumé |
This paper deals with the effects of gesture on the sound signal
produced by an acoustic instrument and the modeling of these gestures.
We
focus on the effects of ancillary gestures, those not primarily
intended to produce sound, but nevertheless omnipresent in
high-level instrumentalists' technique. We show that even in the case
of non-expressive performance of wind instruments, performers'
ancillary gestures appear in the observed sound by means of
strong partial amplitude's modulation. We claim that these
modulations account for a naturalness that is usually lacking in
current synthesis applications.
We have analyzed video recordings of clarinet performers in concert
situations and identified typical gesture patterns. In order to
demonstrate that these gestures are the main cause of the sound
partial's modulation, we have undertaken an extensive set of clarinet,
oboe
and saxophone recordings in different reproducible environments, such
as an anechoic chamber and an variable acoustics auditorium. The
recordings were performed using multiple microphones at calibrated
positions, always including one internal microphone. The notes were also
interpreted in three styles: expressive (quasi-jazz), non-expressive
performance and performance with the instrument kept completely
immobilized by a mechanical apparatus. Simultaneously, experiments
were done in order to determine the exact influence of the
instrument's radiation directivity, of the room reverberation and of
the instrument's mouthpiece. We studied more precisely the
effects of the first reflection on the recorded sound when
the instrument is moved. This was achieved by comparing recordings
performed in an anechoic chamber using a removable wood floor placed
underneath the instrument and the microphone. Finally, we measured the
auditorium response excited by a loudspeaker connected to a
clarinet tube. The tube was then rotated in order to allow a precise
setting
of its position according to standard performer gestures found in the
analyzed videos.
The sinusoidal partials of the sounds were then extracted using an
additive analysis procedure. Partials may exhibit amplitude modulations
of more than 10 dB, even for low frequency partials and in the
case of non-expressive sound recordings.
We show through measurements and theoretical demonstrations that
these modulations are primarily caused by the influence of the
performer's ancillary gestures coupled with the room's acoustical
characteristics. Furthermore, we show that even in highly reverberant
rooms, modulations do not occur in the absence of ancillary gesture.
Mouthpiece and directional characteristics are demonstrated to have
influence only in large amplitude movements, such as in deliberated
movements.
Finally, a real-time synthesis model of a clarinet confirms these
results, where the instrument's radiation pattern and an early room
response model based on measurements of the variable acoustics
auditorium
have been implemented. Sound and video examples of performances using
this
model will be presented during the conference.
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