of Microprocessors

360 MUSICAL ApPLICATIONS OF MICROPROCESSORS
of the curves, a command or function key would be available to suppress
display of all but one or two of the curves.
Also shown is a cursor that can be used to designate a specific point in
time on the functions. The cursor can be easily moved back and forth to find
the area of interest. Any of the input devices mentioned earlier could be used
to move the cursor, even the function keyboard. To aid the user in finding
the audible area of interest, the program could be set up to actually send the
corresponding data to the synthesizer as the cursor is moved.
Each of the seven parameter values, ofcourse, has some kind ofphysical
units, such as hertz for the formant and pitch frequencies. While the exact
value of a parameter may not be as important as its relationship to other
parameters, it is often necessary to know the value more precisely than the
display shows it. Accordingly, the values of each parameter at the current
cursor position is displayed at the bottom of the screen.
For critically comparing two parameters, it is useful to be able to plot
one against another as is done in the bottom right corner. Commands, of
course, would be available to select the parameters being compared. The
curve shown represents the time interval spanning the screen and the emphasized
point represents the current cursor position. One thing the curve does
not show is the time scale, but the user can get a good feel for it by moving
the cursor and noting the corresponding movement of the emphasized point.
It is even possible to have editing functions that operate on this curve (often
called a trajectory) directly.
Editing Functions
Now, how might these curves be edited? Simple sample-by-sample
alteration of a curve should be available but would certainly not be very
productive. Let's first look at the kinds of curve editing that might be
needed and then define editing functions that would make the task easier for
the user. For example, the user might decide that a certain segment of the
sequence moves too fast. A corresponding editing function should therefore
allow the user to point out the time interval to be changed with the graphic
cursor and then stretch it by 10%. At this point, the sequence can be played
for evaluation. This can be made a reversible function by including a corresponding
shrink by 10% command. The user can experiment until satisfied
that any remaining imperfections in the sound sequence are due to other
causes.
Other operations could be defined that act on only one curve. For
example, the amplitude of the white noise may need to be generally increased
in a certain area. Again the interval could be pointed out and a command to
raise all hiss amplitudes in the region by I dB might be invoked. A complementary
decrease by I-dB function makes this a reversible function. A
copy function might be imagined whereby the contour of one curve could be