of Microprocessors

11
CORtrolSequeRce
Display andEditing
One of the unique capabilities of a computer-controlled synthesizer is meaningful
graphic communication with the user. Many of the normally abstract
ideas about sound parameter variation become concrete objects when visualized
through a computer-driven graphic display. As such, they become
much easier to manipulate as well as comprehend. Imagine for a moment
reading the text of this book without the benefit of illustrations. The notions
of waveshape, spectrum shape, parameter variation contours, etc.,
would be difficult to visualize regardless of the quality of exposition. With
figures to illustrate ideas, understanding of the point being illustrated as well
as its relation to other points is made easy, almost natural. "Dynamic"
illustrations in which variables actually move is better yet for understanding
relationships. A graphic display device provides these aids to the music
system user who must constantly conceptualize a myriad of interrelated
parameters and effects in the evolving composition.
Not very long ago one interacted with a computer music system solely
through punched cards. The keypunch machine in the computer center was
the only means available for editing the sound material, which consisted of
music language statements and an occasional tabulated curve. Alphanumeric
display terminals for on-line editing of text were rare, while graphic display
consoles were exceedingly expensive luxuries. Now an interactive alphanumeric
display is expected even on small, inexpensive home systems and
reasonably adequate graphic capability costs less than $500.
Whereas the previously discussed musical input methods concentrated
on getting data into the system in an initial good form, this chapter will
discuss methods for building up a composition from little or nothing
through editing. Editing is a process whereby a body of initial material is
modified or rearranged in response to commands by the user. It also covers
the addition of new material.and the deletion of old or unwanted material.
An ideal computer music-editing system should be able to accept input in a
variety of forms, such as keyboard activity, source signal analysis, algorithmic
sequence generation, and music language statements. It should be
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