Classification
See the ACMC 2009 paper by Tallaine Opie & Andrew R. Brown
After examination of a large number of data sets, a classification of morphological types has been derived similar to the three suggested by Wishart, although we use some different terms to make the meanings more clear. Also a fourth type has been identified. These types will be introduced and discussed in this section. Each form also contains configuration types that help define the musical potential more accurately.
Each type will be labelled as a form, as this is more suggestive of an encompassing type, which holds many variations on similar themes. It must be noted that there is no ideal form in eco-structuralism as change and variation is integral to all forms of music.
Eco-structural forms are currently classified by generating a graph of the data, and then visually examining and comparing this to the forms below to find the best match. They need to be analysed in a visual manner because they no longer contain an audio component. Other possible methods of analysis will be discussed later. The compositional potential applies only to the attribute data. The data could be used to create tones, resynthesise sounds, control synthesiser and effect parameters, designate musical notes, dynamics, articulation and musical sequences, or control the macrostructure of a musical composition, etc.
Classification Types:
The Steady Form:
Description: Relatively flat data. Can contain some minor discrepancies.
Graphical Example: Data derived from the spatial attribute study of a very short stereo segment of a recording of an ocean wave as it approaches, but before it crashes.
Figure 1: The Steady Form in Ascent.
Configurations: Ascent, Plane, Descent.
Compositional Potential: Stasis, Stability, Drone, Basso Ostinato.
Notes: The steady form is similar to what Wishart termed continuous, although continuous can be misleading as all sounds can be continuous in any number of forms. Finding stable forms in natural sounds is quite rare. R. Murray Schafer points out that only man made devices will emit an unchanging audio signal [15]. This is of course far from ideal as the musical potential would be quite dull, unless it was combined with something less steady. The term stable might have been used, but stability implies a certain accuracy and reliability that steady does not. A signal can be steady without being stable, reliable or accurate, which is more functional in this context.
The Iterative Form:
Description: Mostly patterned data.
Graphical Example: Data derived from the amplitude attribute study of a mono recording of waves crashing on the beach.
Figure 2: The Iterative Form, Rectangular.
Configurations: Rectangular, Sinusoidal, Triangular.
Compositional Potential: Motif, Melody, Harmony, Macrostructure, Effects, Curves, Smooth Transitions, Repetition.
Notes: This is the same term used by Wishart. The form is characterized by identifiable symmetry and repetition. The presence of iteration, or repetition, in music is well understood. Indeed the ability of humans to tolerate repetition in music is surprising given our quick boredom with it in other media such as language, visual design, and haptics.
The Unstable Form:
Description: Fluctuating data in a mostly rough manner, but still with some linearity.
Graphical Example: This data was derived from the dominant frequency attribute study of a mono recording of a babbling brook.
Figure 3: The Unstable Form, Sinusoidal.
Configurations: Fluctuating, Rectangular, Sinusoidal, Triangular.
Compositional Potential: Fluctuation, Solo, Macro-structure, Effects, Surprise, Variety.
Notes: Wishart refers to this form as unsteady. The term unstable has been used instead of unsteady as it is more familiar. Data with this form can be used to provide interest and variation particularly in moderate amounts and as a modulation source for steady or iterative forms.
The Impulse Form:
Description: A discrete impulse that does not match the surrounding data.
Graphical Example: Data derived from the amplitude attribute study of a mono recording of a campfire crackling.
Figure 4: The Rapid Sharp Impulse Forms.
Configurations: Blunt, Sharp, Rapid, Rare.
Compositional Potential: Switch, Gate, Trigger, Pulse.
Notes: The impulse form is one not discussed by Wishart, although after analysing various data streams, it is apparent that this phenomena crops up quite regularly. If the impulse occurs multiple times in one stream it may be useful to describe the periodicy of the impulse. The actual sample used here in the example is a graphical representation of a crackling campfire. The sound will be familiar to everyone. From a distant perspective the sound of the crackling fire seems quite steady. There is a lull to it that seems constant and unchanging. On closer inspection however, there appears to be two layers at work. There is a steady floor, which is the dim humming of the small flames, but interspersed is an unstable impulse which punctuates the sound. Each impulse is quite similar, so it could be stated that there is an iterative unstable impulse. That impulse is the sound of a crackle. Because they occur quite regularly and are similar in impulse, they only appear as an impulse on close inspection. Another example of a similar combined form that occurs naturally is a thunder storm. The rain forms a steady floor, which is punctuated by unstable impulses of thunder.
As the fire sound example illustrates, these archetypal forms will rarely be found in data from natural sounds. Much more likely is the use of this classification language as a way of describing aspects of a data stream and tendencies of the structural morphology. Clearly there will be a vast number of combination forms, including second order descriptions of stable or iterative combinations and so on.
Combinations:
Description: Data that seems to switch between two or more forms.
Graphical Example: Data derived from the dominant frequency attribute study of a babbling brook.
Figure 5: Unstable Sinusoidal with Fluctuating Sharp Impulse Combination
Configurations: Fluctuating, Dissipating, Accumulating.
Compositional Potential: Solo, Variety, Fluctuation, Macrostructure.
Notes: The use of the combination has already been described in the previous form, whilst explaining the thunder and crackle impulses, there are however multiple combinations that could occur. This example structure could be described as unstable with unstable impulses.
There is a final point to make about the classification of a data stream as exhibiting particular structural characteristics, and therefore particular compositional opportunities. The scale at which the data (or sound) is examined may change our perception of morphological characteristics. Consider again the example of the fire sound. As depicted it appears as an unstable series of impulse forms. However, the time slice under review is very short, this is a description of its micro structure. Zooming out to a larger time scale, a crackling fire provides a stable, but interesting, background texture. This is the kind of analysis that is assisted by the language of form categories and highlights the creative utility of this approach for the eco-structuralist composer.