ï~~and range used to produce sound. In turn, the sound reflects, in some way, the effort or energy used to create
it. The fact that brass tones add upper partials as they grow louder is a classic example.
Each part of the body has its unique limitation in terms of direction, weight, range of motion, speed and
force. In addition, actions can be characterized by ease of execution, accuracy, repeatability, fatigue, and
response. The underlying physics of movement lends insight into the selection of musical material. Thus, a
delicate curling of the fingers should produce a very different sonic result than a violent and dramatic leg
kick, since the size, weight and momentum alone would have different physical ramifications. To do this,
physical parameters can be appropriately mapped to musical parameters, such as weight to density or
register, tension to dissonance, or physical space to simulated acoustical space, although such simple oneto-one correspondences are not always musically successful. The composer's job then, is not only to map
movement data to musical parameters, but to interpret these numbers to produce musically satisfying
results.
The stage, room, or space also has its boundaries, limiting speed, direction, and maneuverability.
Psychological intensity increases or decreases with stage position, as the audience perceives more energy
and focus as the performer moves upstage. Apparent gravity pulls the performer downstage with less effort,
in a way similar to the very real pull of vertical downward motion. Intensity may also vary with the
amount of activity confined to a given space. These physical and psychological properties of space are ripe
for musical interpretation.
Being aware of the underlying physics of movement does not necessarily imply an obvious musical
solution. Indeed, since computers are only simulating real world events, tampering with the apparent laws
of physics is a luxury made possible in virtual environments. By being aware of these laws, it is possible
to alter them for provocative and intriguing artistic effects, creating models of response unique to the
computer. More furious and strenuous activity, for example, could result in quieter sounds and silence. At
the same time, a small yet deliberate nod of the head could set off an explosion of sound. Such "unnatural"
correlations makes motion all the more meaningful.
Use in Interactive Music Systems
Interactive music systems use software to interpret human action to effect some aspect of music generated or
modified by computers. Typically, musical material, in the form of MIDI data, is analyzed for musical
features such as tempo, rhythm, or intervals. However, movement data is equally effective, and has been
frequently used as input to interactive music systems. Movement data may be filtered, scaled, or selected in
preparation as parameter input to compositional algorithms. Performer's actions may translate into
immediate musical results, they may have delayed reactions, or they may be analyzed over longer spans of
time for direction, repetition, and other patterns. Influences may be used in a less obvious manner when
applied to the unfolding of higher level events in more fully developed musical environments.
These techniques give performers the feeling of participating, along with the computer, in the creation of a
musical work. The feeling of interactivity depends on the amount of freedom the performer has to produce
and perceive significant results, and the ability for the computer to respond in a way that makes sense and
and naturally elicits the performer's participation. Highly interactive systems are more complex but
potentially rewarding. With more parameters available for change, performers will need extra practice time
to "learn by ear" the idiosyncrasies of a system capable of intricate connections between movement and
music. The computer's response must be believable in the sense that it seems appropriate for the action
taken, and appropriate for the style of music and movement. Interactive music succeeds when it encourages
spontaneity while residing within the boundaries of a dynamic artistic context that is whole and engaging.
The quality of interaction lies on a continuum. On the low end lie predetermined sequences or sound files
that are triggered by a performer. While robust branching structures and mixing capabilities allow the
performer to experience musical selection, the samples or MIDI files, when triggered, produce the same
results. A predetermined score could be made slightly interactive by allowing a performer to control only
one parameter of the music, such as the tempo or dynamics. Highly interactive pieces are less predictable
since the performer controls many more significant musical parameters. The composition can change
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