of Microprocessors

DIRECT COMPUTER SYNTHESIS METHODS 123
the user can actually think in terms of standard voltage-controlled modules
but with functions, accuracy, range, and quantity impossible to achieve
with real modules.
The actual music language associated with MUSIC V is quite different
from that of NOTRAN. In particular there is no parallel with standard
music notation. Instead, all of the information is in terms of physical sound
parameters such as frequency in hertz, amplitude in volts or decibels, time in
milliseconds, etc. Often tables of values are used to specify how each of these
parameters are to change with time during an event.
The MUSIC V processor is actually configured into threepasses or scans
of the input data. During pass one, the services of a macroprocessor program
are available to allow certain repetitive statements to be generated under the
control of higher-level parameters. Also done during pass one is instrument
definition as a combination of predefined modules called unit generators.
Integration of parameters in graphic form into the score is also possible. One
unique feature of the MUSIC V system is that during pass one the statements
describing instruments and notes do not have to be in time order. This
feature makes the macroprocessor more flexible and easily applied.
Pass two is a sorting program that sequences the output from pass one
into strict time sequence. At this point, some additional processing of
parameters that influence a number of sequential notes can be performed,
since the statements are in time sequence. For example, time scale shifts for
retards or fine frequency ratio control among simultaneous notes would
normally be done during pass two.
Pass three is the actual language interpreter and sound generation
program. It works much like the NOTRAN interpreter just described except
that it is much more sophisticated. One or two streams of samples may be
produced for monophonic and stereophonic sound, respectively.
Extending the MUSIC V system is much less restriered than with
NOTRAN. Most desirable expansions amount to writing additional processing
programs for pass one. For example, it would be possible to write a
processor that would convert a NOTRAN score into equivalent MUSIC V
complete with equivalent voices constructed from available unit generators.
Additional unit generators or even entire instruments that are not conveniently
described in terms of unit generators could also be added to pass three.
Loosely Structured Systems
Looking again at loosely structured systems, the data base is seen to be
the most important component of the system, in fact, the only link (hat
holds it all together. Several different kinds of data can be kept in the data
base. Using a hypothetical system as an example, it is obvious that sample
data representing a previously computed piece or sampled natural sounds
would be present. Curves of all sorts such as amplitude envelopes, spectrum