ï~~2.
MAKING OF AN INSTRUMENT
2.1 Implementation - a true collaboration!
We aimed at a modelisation that would closely match the
properties of a real bass-clarinet, complete with reed,
mouthpiece, tube, bell and 32 holes (last hole being the
bell). A true bass-clarinet from the company BuffetCrampon was taken apart and its geometric dimensions
measured. With a set of MatLab scripts these data where
used to calculate a mesh using the finite-element method
of representing 3D objects [5]. This actually modelled the
whole interior air-column of the bass-clarinet as one single
composite object (see figure 2). The mesh was then turned
into modal data (mode-frequencies, mode-losses and
corresponding mode-shapes) which Modalys can read
directly from a file. This data now represents one big
resonant object, whose impedance-curve match that of the
measured true bass-clarinet with all keys closed. This work
was undertaken by the team for acoustics of musical
instruments (IRCAM).
Modalys represents many interfaces (MatLab, LispWorks,
OpenMusic, MaxMSP) that can co-communicate. The
model was read from file into a Lisp-script in order to
create all necessary accesses, additional objects (reed,
keys), connections (normalised-valve, hole-connections)
and controls (dynamic controllers for all parameters).
Apart from being non-RT the Modalys Lisp-version is a
perfect user entry. Once executed this lisp-code produced a
final textual script that can be run in realtime from
MaxMSP (using the extern modalys-) applying valuechanges to all predefined controls via messages. No
further definitions takes place, one "plays" ones
"instrument". Special care was taken to create a flexible
reed on a detachable mouthpiece, and to make the holeinteraction as simple as possible. The final instrument has
about 40 interactions, approx. 50 primary physical
parameters and 90 secondary parameters to be controlled
in realtime.
2.2 How to blow the instrument?
The instrument is blown by augmenting an air-pressure
parameter (called gamma in a normalised valve model) to
a critical value. Air-pressure is really a time-dependent
parameter one has to vary in a smooth fashion. Abrupt
changes are likely not to work and high air-pressure values
may likewise block the reed from vibration. Each register
demanded air-pressure and embouchure to be adopted
differently. Multiphonics had usually their own settings.
The time spend in establishing which blowing would work
for which fingering tells how delicate blowing really is - as
in real life!
Holes are opened by setting the appropriate holeweight to non-zero thus activating the hole-connection.
When hole-weight is set to zero the hole is closed and the
hole-connection will be deactivated (freezed) in order to
save CPU. All holes had the sasme initial parameters
tuneable from the interface. Each hole radiates a certain
amount of energy that will be added to the final sound
when the hole is open. The two register-keys where
however treated with the cheaper speed-connections as
their radiation do not contribute to the sound. A key-tohole mechanism was not included in the model. Instead a
scheme for all conventional fingerings for corresponding
opening and closing of holes was saved as presets for
instant recall. Forked fingerings found in methods where
usually created as variant of regular ones and saved as
presets.
2.3 Completing the instrument
A special feature allows the mouthpiece to be detached
from the rest of the tube - while playing and still
sounding! This procedure would not be possible in real
playing and thus shows an example of how the virtual
instrument can extend the real one. The idea of gradual
coupling / decoupling has required the implementation of a
weight parameter in all connections. The weight parameter
can grade the connection from fully connected to fully
Figure 2.
A mesh of the interior air-column of a bass clarinet.
Holes "turn" outward as miniature air-columns.
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