of Microprocessors

698 MUSICAL ApPLICATIONS OF MICROPROCESSORS
if longer. After all events in the statement are processed, the current shortest
will be the actual shortest, which is then passed as an argument to the Level 2
ECB scanner routine.
Level 4 Routines
The preceding has described a functionally complete direct digital
music synthesis system that is quite usable as is. However, even higher-level
programming can be added to further ease its use and reduce the amount of
typing effort needed to encode a score. In a nutshell, Level 4 programming
accepts a string of "extended NOTRAN" statements as input and produces a
longer string of "basic NOTRAN" statements as output. This Output string
is then run through the synthesis program (Levels 1-3) as a separate operation.
The details of Level 4 programming will not be described, but perhaps
a discussion of some ideas and possibilities will give a hint of what could be
accomplished.
One easy-to-incorporate enhancement would be a key signature capability.
A new control statement would be added whereby the user could specify
the key in which the music was written. Note statements then could be
coded without explicit sharps and flats except where necessary. The Level 4
processor would provide all of the accidentals in the output score. It might be
necessary to provide a semipermanent override capability, however, to cover
atonal and highly modulated scores. As mentioned before, other redundancies
such as octave selection could also be removed with similar facilities.
A somewhat more complex enhancement would be a transposition
facility. Orchestral scores, for example, are written for instruments that
actually sound pitches different from what the score says (and the player
thinks). A B-flar trumpet, for example, sounds B-flat when the player reads
and fingers C. The rrumpet part of the score, therefore, has been adjusted so
that the correct pitches are played. With transposition capability, one could
declare that voice 3, for example, was a B-flat voice and therefore directly use
notes from a B-flat instrument score.
Sophisticated sequence control could also be added. Simple repeats and
jumps are obvious but a subroutine capability can allow many weird and
wonderful things to be done. Like a software subroutine, a musical subroutine
can be written once and then called by name whenever it is needed.
Power comes from the fact that a subroutine can in turn call another one and
so on. Thus, very complex sequences can be built up from a relatively small
number of statements. Much of the usefulness of software subroutines is due
to the ability to pass arguments that then alter the action of the routine in a
specific way for that particular call. Arguments such as key signature, pitch
register, tempo, and voicing would allow great variety in the expression of a
musical subroutine without rewriting it. Some really nice effects can be
accomplished if a single voice line can be subroutined independent of other
simultaneous voice lines.