Applied Acoustics Systems Chromaphone 3 Upgrade Acoustic Object Synthesizer Plug-In (Download) - Manual (Page 39)

5.3 The Synth Section 39
Figure 22: Contour plot corresponding to normal mode [1,1] and [3,2] of a plate.
But this is not all, we can distinguish different types of objects, such as a vibrating plate and a
beam, but also two objects of the same type but made out of different material. For example a metal
plate will sound brighter and have a longer decay than a wooden plate. This is due to the fact that
the physical properties of an object depend on its material which determine the relative
amplitude
and phase of the different partials as well as their damping, a measure of how fast they will decay
once excited. The specific amplitude, phase and damping of each partial therefore determine the
specific tone of the object as well as how it evolves with time.
There is finally one more parameter which affects how an object sounds, it is the point of
excitation. Indeed, a drumhead does not sound the same if it is hit in the middle or near the rim
of the drum. This can be understood by the fact that exciting an object on a point located on a
nodal line of a mode (a line where amplitude of the motion associated with a mode is zero) does
not allow the transfer energy to that specific mode and its corresponding partial will not be excited.
The effect will not be as pronounced but will still exist as the excitation point is moved around the
nodal lines which explains how the excitation point influences the relative amplitude of the partials
and therefore the tone.
Coupling of Resonators
One of the key features of Chromaphone is that it allows one to couple objects together, in other
words to take into account the interaction between objects as opposed to simply feeding the signal
from one object to the other. This is very interesting because this interaction between components
results into a new object which, while being related to its original elements, behaves and sounds
differently. In fact, musical instruments are based on combinations of objects such as a string and
a soundboard for a guitar, a bar and a tube in the case of a vibraphone or a skin and a column of air
in a drum.