of Microprocessors

38 MUSICAL ApPLICATIONS OF MICROPROCESSORS
host of keyboard instruments such as the Novachord (1938) and the
Melochord (949). In the early 1950s, however, work began on a general
purpose instrument, the first electronic sound synthesizer.
The RCA Mark II Electronic Music Synthesizer could produce two
tones at once in which all of the important parameters could be controlled.
The control mechanism was a roll of punched paper tape, much like a
player-piano roll. Thus, it was a programmed machine and as such allowed
composers ample opportunity to carefully consider variations of sound
parameters. The program tape itself consisted of 36 channels, which were
divided into groups. Each group used a binary code to control the associated
parameter. A typewriter-like keyboard was used to punch and edit the tapes.
Complex music could be built up from the basic two tonr;s by use of a
disk cutting lathe and disk player, which were mechanically synchronized to
the program tape drive. Previously recorded material could be played from
one disk, combined with new material from the synthesizer, and re-recorded
onto another disk.
The RCA synthesizer filled a room, primarily because all of the electronic
circuitry used vacuum tubes. Financing of the project was justified
because of the potential for low-cost musical accompaniment of radio and
television programming and the possibility of producing hit records. Extensive
use ofthe machine emphasized the concept that programmed control was
going to be necessary to adequately manipulate all of the variables that
electronic technology had given the means to control.
Direct Computer Synthesis
The ultimate in programmed control was first developed in the middle
1960s and has undergone constant refinement ever since. Large digital computers
not only controlled the generation and arrangement of sounds, they
generated the sounds themselves! This was called direct computer synthesis of
sound because there is essentially no intermediate device necessary to synthesize
the sound. The only specialized electronic equipment beyond standard
computer gear was a digital-to-analog converter (DAC), a comparatively
simple device. Simply put, a DAC can accept a string of numbers from a
computer and plot waveforms from them as an audio signal suitable for
driving loudspeakers or recording.
Such a system is ultimately flexible. Absolutely any sound within a
restricted frequency range (and that range can easily be greater than the range
of hearing) can be synthesized and controlled to the Nth degree. Any source
of sound, be it natural, electronic, or imaginary, can be described by a
mathematical model and a suitable computer program can be used to exercise
the model and produce strings of numbers representing the resulting
waveform. Sounds may be as simple or as complex as desired, and natural
sounds may be imitated with accuracy limited only by the completeness of
the corresponding mathematical model.