of Microprocessors

CONTROL SEQUENCE DISPLAY AND EDITING 359
independent parameters are to be controlled. Four of these are the center
frequencies of the four bandpass filters used to simulate the first four formants
of speech. Two more are used to control the amplitude of the voice
(buzz) and noise (hiss) sources. The last determines the pitch of the voice. It
is assumed that a multiple-channel DAC has been connected to the computer
so that the synthesizer modules can be controlled. For an application such as
this, 50 to 100 updates of the parameters per second should be sufficient.
While experts in the field might argue the completeness of this model
for producing a convincing singing voice, it is the author's belief that precise
control of the parameters available is often more important than the number
of parameters being controlled. The purpose here is to understand how
interactive graphics can be utilized to quickly determine how these seven
parameters should be varied to obtain the desired result. Further details
concerning speech synthesis theory and practice are abundantly available in
the references.
Figure 11-7 shows what a graphic display representation ofa portion of
these seven control functions might look like. The horizontal axis is time and
the vertical axes depend on the particular curve. With all seven functions
shown at once, it is easy to see the relationships that exist among the
functions. When more detail is required, such as when actually editing one
F4
F3
F2
FI
FV -----..... , .....+-_--'/
AV~
FV=117
AV=-6
AN=-40
""'-J
F4= 2730
F3= 1430
F2= 816
FI = 310
\'-"'-----
--.........._---
AN........... ~/.---
-------+-_/ '-..._--~-_ .... /
TIME = 56.17.23
~lfr:.
Fig. 11-7. Typical display of portion of speech synthesis sequence
FI