Operation Manual

6.46 Multimode 107
and mechanics and is used to describe complex vibrational motion using modes (elementary os-
cillation patterns which can be used to decompose a complex motion). By adding together modes
of different frequencies, amplitude and damping, one can reproduce the behavior of different type
of structures. The accuracy of the resulting signal depends on the number of modes used in the
simulation.
The Multimode module is not directly accessible to the user. Rather, other
modules such, as String, Plate, Beam, Marimba and Membrane, use the Mul-
timode as their front. These other modules first calculate the different modal
parameters corresponding to their respective structure type as requested at con-
struction time and, next, call the Multimode module in order to implement the
parameters they require. Since these different object types are based on the same
underlying simulation technique, they all have the same number of inputs and
outputs and share the same controls (which appear on their front panel) for ad-
justing their physical properties.
Amplitude
The amplitude control is simply a gain which controls the amplitude of the output signal. It can be
adjusted with the amp knob on the front panel.
Decay
The damping of an object affects the decay time of the sound produced by the object. This param-
eter is adjusted using the decay knob on the front panel. When the knob is turned left, the damping
is high and the decay time short; damping is low and decay time is long when the knob is turned
right. The damping is characteristic of the material of the object. Damping in wood, for example, is
high and the decay time is short (knob turned to left) and in steel damping is lower and, therefore,
decay time is longer (knob turned to right). But damping also varies for a given material depending
on how the object is used or connected to other objects. The oscillation of a string, for example,
has a much shorter decay time when used on a violin than on a mandolin.
Playing frequency
The frequency of the sound produced by an object is dependent on its “useful” size. A large metal
plate, for example, produces a sound with a lower pitch than does a smaller one. The pitch of the
output of a Multimode object is determined by the signal entering the pitch input appearing on
every such object. In other words, the size of the object is varied in order to obtain the requested
pitch. The mod knob is a gain knob affecting the amplitude of the pitch input signal. When in the
center position (green LED on), the gain equals 1 and the pitch variation is equal to 1 Volt/octave.
This position is used to play an equal temperament scale when connecting the pitch output of a
Keyboard to the pitch signal input of a Multimode object.