Operation Manual

4.3 The Mallet Module 23

of the string; most of the energy will be reﬂected back into the string at the bridge resulting in

a standing wave in the string and a long decay. Now let’s imagine that the soundboard becomes

much less rigid. The string can now set it into motion more easily at the bridge. This implies that

more energy will be able to ﬂow from the string to the soundboard resulting in a shorter decay as

less energy is reﬂected back into the string. But the soundboard also moves according to its own

vibration modes which are different from that of the string. This motion interacts with that of the

string which modiﬁes the tone that we hear. One could say that we now hear more the soundboard

in the resulting sound. The amount of coupling between the resonators therefore affects both the

resulting tone and its decay time.

The material of the objects is not the only thing to consider. Their respective tuning, which

can be related to their geometry, also greatly inﬂuences the response of the combined objects. For

example if the objects are tuned at the same fundamental frequency, their respective motion will

be synchronized and result in a sound having a large amplitude. For example, in a vibraphone,

the tubes are tuned to the fundamental of the bar above them in order to amplify the fundamental.

But there is also another effect which might seem contradictory at ﬁrst. The fact that energy is

well transmitted from the bar to the tube also implies a faster decay of the oscillations. Hence,

the overall effect of the combination of the bar and the tube is to amplify the fundamental while

decreasing the decay time of the note.

As we can see, the overall effect of coupling can be quite complex as many factors must be

taken into account. As a rule of thumb, in traditional musical instruments, a ﬁrst resonating object

with a long decay is usually coupled to a second resonator having a very short decay time (try

knocking on the sound board of a guitar) in order to avoid unpleasant resonance effects.

4.3 The Mallet Module

The Mallet module is used to simulate the force im-

pact produced by a mallet striking an object. The force

of the impact is adjusted with the Volume knob while the

stiffness of the mallet (related to its material) is varied

with the Stiffness knob. Figure 9 shows the effect of the

adjustment of the stiffness on the output signal. As the

stiffness is increased the excitation signal becomes narrower. The effect of the Volume parameter

which determines the amplitude of the impact is also shown in the same ﬁgure. These values can

be modulated with the MIDI velocity and the note played. These modulation are usually used to

get a stronger impact with increasing keyboard velocity and to make the mallet softer as the im-

pact velocity increases, a behavior one observes, for example, on piano hammer heads due to the

non-linearity of the felt.

Noise can also be added to the impact sound allowing for some interesting effects. The amount

of noise is controlled with the Noise control. In its leftmost position there is no noise added to the

signal and one only hears the impact noise. Turning this knob clockwise gradually increases the