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Exploring Sound-Producing Actions

Here, we introduce the affordance concept, the structure of an attack, and Schaeffer's categories of sound-producing action.
© Alexander Refsum Jensenius, University of Oslo
We shall here look at some terminology used to describe sound-producing actions.

Objects and Actions

Sounds are produced when actions work on two or more objects, which is often called interaction. We may therefore think of this as an object-action-object system, as illustrated in the figure below.
An object-action-object system
In nature, the features of such a system are defined by the acoustical properties of each of the objects involved in the interaction (such as the size, shape and material), and the mechanical laws of the actions that act upon them (such as the external forces and gravitational pull). It is our life-long experience of acoustical and mechanical properties of objects and actions, that makes us able to predict the sound of an object-action-object system even before it is heard.

Affordance of Sound-producing Actions

To use Gibson’s affordance concept again, we may say that an object-action-object system affords a specific type of sonic result. For example, when we see a drummer hit a drum with her stick, we know that we will hear a drum sound because we have seen (and heard!) drums before. Think of any instrument (or other object for that matter), and you can probably imagine how it will sound.
Even more, you can probably think of many different sound-producing actions to use with one particular instrument, hitting, sliding, blowing, and so on. And you can use many different objects to interact with your instrument, such as a mallet or a bows. As you can easily imagine, there are endless combinations of such action-sound couplings. The remarkable thing is that we are able to imagine and predict the sonic outcome of such couplings. Our main argument here is that this embodied knowledge is deeply rooted in our cognitive system.

From Brain to Sound

So far we have only discussed the perception of sound-producing actions. But we may also think of a chain describing the production of such actions. The figure below shows the action-sound chain from cognitive process to sound, and with feedback in all parts of the chain.
Action-sound chain
The chain starts with neurological activity in the brain, followed by physiological activity in a series of muscles, and biomechanical activity in limbs of the body. The interaction between the body and the object occurs as an attack when an element of the object (for example a drum membrane) is excited and starts to resonate.
The feedback in the chain is important, as it is part of the action-perception loop. It is this constant feedback from all our parts of the body that make us able to adjust our actions continuously. For example, just think of how a jazz drummer is constantly able to adapt the playing to make the best sound from the drums and to pick up on the musical elements of the other musicians.

Excitation, Prefix, Suffix

If we zoom in on only the “attack” part of the chain depicted above, it can be seen as consisting of three elements: prefix, excitation and suffix.
Excitation, Prefix, Suffix
The prefix is the part of a sound-producing action happening before the excitation, and is important for defining the quality of the excitation. The suffix is the return to equilibrium, or the initial state, after the excitation.
The prefix, excitation and suffix are closely related both for the performance and the perception of a sound-producing action. Following the idea of our perception being based on an active action-perception loop, a prefix may guide our attention and set up expectations for the sound that will follow. For example, when we see a percussionist lifting the mallet high above a timpani we will expect a loud sound. We will also expect the rebound of the mallet (the suffix) to match the energy level of the prefix, as well as the sonic result. As such, both prefixes and suffices help to “adjust” our perception of the sound, based on our ecological knowledge of different action-sound types.

Action-Sound Types

The French composer and musicologist Pierre Schaeffer was a pioneer in defining a structured approach to thinking about musical sound. We will here build on his concept of three main types of sounds:
  • Impulsive: sounds characterised by a discontinuous energy transfer, resulting in a rapid sonic attack with a decaying resonance. This is typical of percussion, keyboard and plucked instruments.
  • Sustained: sounds characterised by a continuous energy transfer, resulting in a continuously changing sound. This is typical of wind and bowed string instruments.
  • Iterative: sounds characterised by a series of rapid and discontinuous energy transfers, resulting in sounds with a series of successive attacks that are so rapid that they are not perceived individually. This is typical of some percussion instruments, such as guiro and cabasa, but may also be produced by a series of rapid attacks on other instruments, for example rapid finger actions on a guitar.
It is important to note that many instruments can be played with both impulsive and sustained actions. For example, a violin may be played with a number of different sound-producing actions, ranging from pizzicato to bowed legato. However, the aim of categorising sound-producing actions into three action-sound types is not to classify instruments, but rather to suggest that the mode of the excitation is directly reflected in the corresponding sound.
As shown in the figure below, each of the action-sound types may be identified from the energy profiles of both the action and the sound.
Action-sound types
Here the dotted lines indicate where the excitation occurs. Note that two action possibilities are sketched for the iterative action-sound type, since iterative sounds may often be the result of either the construction of the instrument or the action with which the instrument is played. An example of an iterative sound produced by a continuous action can be found in a cabasa, where the construction of the instrument makes the sound iterative. Playing a tremolo, on the other hand, involves a series of iterative actions, but these actions tend to fuse into one superordinate action. In either case, iterative sounds and actions may be seen as having different properties than that of impulsive and sustained action-sound types.

References

© Alexander Refsum Jensenius, University of Oslo
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