User's Manual

46 The Editor View
thereby removing more and more low frequency content in the sound.
The Radius parameter replaces the Material control when a Tube object is selected. In fact,
standing waves in a tube do not result from the vibrations of the walls of the tube but rather by
vibrations of the air column inside the tube. The material of the tube is therefore not a relevant
parameter in that case. The effect of the Radius parameter can be viewed as that of a high-pass
filter with the cut-off frequency of the filter increasing as the radius of the tube is decreased. In
other words, the smaller the radius, the brighter the sound. The radius of the tube also affects
the total decay time of the object, the decay time being shorter for large radii as a result of larger
radiation losses at the open ends of the tube. The Radius control on the interface has been adjusted
to follow the same behavior as that of the Decay one, in other words to obtain longer decay time
as it is turned clockwise. Even if this may seem contradictory at first, this implies that the actual
radius of the object decreases has the value of the parameter is increased.
The Hit Position controls where the excitation signal is applied on a resonator. This is an im-
portant parameter as it affects the relative amplitude of the different partials of the resonator and
therefore the spectrum of the sound it radiates as explained in Section 5.3.1. This position is indi-
cated as a percentage of the total size of the object. The minimum value of the control corresponds
to an excitation applied on the border of the object while the maximum value corresponds to an
excitation applied on its center. In the case where both resonators are coupled, the Hit Position set-
ting of resonator A represents the location where the excitation signal is applied while this setting
on resonator B represents the point where the extremity of Resonator A is coupled to resonator B.
As the tone of the resonator varies with the excitation position, it is interesting to modulate this
position while playing. This is possible using the Vel, Key controls which are used to adjust the
amount of modulation from the keyboard velocity, pitch signal respectively and the Rnd control
which applies a random modulation.
The Coupling selector is used to determine if the two resonators are coupled or not. In the Off
position, the resonators are not coupled and excited simultaneously. They are, in other words, in
a parallel configuration. The output signal is then a mix of the signals from the two resonators in
a proportion determined by the setting of the Balance slider. When in its center position, an equal
amount of signal from resonator A and B is present in the mix. More signal from resonator A or B
is obtained by adjusting the balance slider up or down.
The two resonators are coupled when the Coupling control is in the On position. In this case,
resonator A receives the excitation signal and energy is exchanged between the two resonators
through coupling which creates a new object whose characteristics depend on the parameters of the
two objects. In coupling mode, the Balance slider is used to adjust the impedance ratio, in other
words how easy it is to set one object into motion compared to the other. In the A position, the
impedance of resonator A is lower than that of resonator B implying that resonator B is very stiff
compared to resonator A. As a result, most of the energy is reflected back into a at the junction point
and resonator A is not much affected by resonator B; one mostly hears resonator A. Increasing this
parameter decreases the impedance of resonator B with respect to that of resonator A affecting
more and more the functioning of the first resonator. Below the center position, the impedance
of resonator B is lower than that of resonator A resulting in a change in the limit conditions of