of Microprocessors

MUSIC SYNTHESIS SOFTWARE 693
though it is not producing an audible sound. Again, exceptional condition
testing is probably necessary to eliminate the effects of this kind of error. The
testing can be relatively infrequent, however.
Control Statements
The basic level of NOTRAN has very few control statements. Many
more would undoubtedly be added if the language is extended via a macroprocessor.
One of the basic control statements is the TEMPO statement. The
TEMPO statement essentially specifies a correspondence between musical
time in terms of quarter notes, etc., and real time. The statement format is
simply the keyword TEMPO followed by a valid duration specification (see
the section on note statements), an equals sign, and a number specifying the
number of milliseconds assigned to that duration. An example statement is:
TEMPO Q=350
where Q refers to a quarter nate and the 350 specifies that the quarter note
has a duration of 350 msec. If the time signature (which does not need to
be specified) is 4/4, then this cOtresponds to a metronome marking of 170
beats/min.
The only other control statements are START and STOP. These
keywords require no parameters and are merely used to skip over code while
the score is "debugged." Sound generation is started when a START statement
is encountered and suspended when a STOP statement is seen. With
sound generation suspended, statements are interpreted and thrown away at
great speed, thus allowing rapid syntax checking or skipping of sections
known to be correct.
Comment lines may be inserted simply by making the first character on
the line an *. The interpreter then ignores the remainder of the line and goes
ro the next.
Note that there are no jump or repeat statements and no provisions for
subroutines (refrains) in the basic language. A little thought will reveal that
if these are implemented in the Level 3 interpreter that the entire NOTRAN
score would have ro be in memory at once. During actual sound synthesis
much, if not most, of memory will be needed for waveform tables, control
blocks, and sample buffers. Although the text could be kept on disk and
randomly accessed in response ro a jump or refrain statement, such a facility
is beyond many microcomputer operating systems. In any case, these functions
will be left to a higher-level macroprocessor that has all of memory
available when run.
Note Statements
Note statements are the only ones that actually produce sound and take
real time to execute. Whereas the other statements all began with a keyword,