of Microprocessors

CONTROL SEQUENCE DISPLAY AND EDITING 357
Most personal computers, however, don't have the luxury of a separate
function keyboard, but many do have from 4 to 10 function keys added to the
standard layout. These are typically placed in a single- or dual-column to the
left or a single row above the main key array. The latter arrangement allows
for displaying legends at the very bottom of the screen that line up with the
function keys when the keyboard is positioned right. The interactive
graphics program (or text editor or just about any kind of interactive
program) can then dynamically change the legends as the program changes
modes. This has proven very effective in the Micro Technology Unlimited
line of computers and others.
A similar option that works well with a light pen, mouse, or other
pointing device, is to display a menu of function options that the user then
"points" to. In a complex program, only a few such soft keys may normally
appear in a dedicated area of the display, but, when more are temporarily
needed to qualify an earlier selection, part of the screen image can be saved
and overwritten with the temporary menu. These are often called pull-down
menus because of their appearance when the normal menu is at the top of the
screen. In systems with sufficient display resolution, interactive programs
designed for first-time users may even dispense with words for the legends
and substitute little pictures called icons. Extensive use of such conventions
was first popularized by the Apple McIntosh computer and has since become
relatively common.
Composition by Editing
Now that the tools used in interactive graphics have been described,
let's look at how these can be used to communicate musical and acoustical
ideas to a computer-based synthesis system.
First, consider a case in which direct control of several sound parameters
simultaneously is desired. Further assume that the exact shape of the
variatioh contours and their interrelation is critically important in creating
the desired audible result. To make matters more difficult, the shape of the
required contours is only roughly known. Finally, the rapidity of the variations
is such that real-time manual control is out of the question. What has
been described is a perfect example of synthesizing a realistic singing voice,
although the concepts apply to any complex, rapidly changing sound.
Composition by editing is best done if one starts with some approximation,
no matter how coarse, of the desired results. In realistic speech
synthesis one might start by analyzing natural speech into the parameters of
interest. Even if the goal is a female singing voice and the input is a
gravel-throated male voice, the set of parameter variations that results is close
enough to the final result so that the necessary editing changes are somewhat
apparent. One might also use a "speech synthesis by rule" program, which
accepts a phonetic spelling and produces a first cut at the values needed.