of Microprocessors

778 MUSICAL ApPLICATIONS OF MICROPROCESSORS
envelope shapes and periodic updating of the amplitude register contents, any
kind of envelope can also be added to the tones. For dynamic spectta sounds,
the included software could combine from two to four oscillators, each with a
different waveform table and delayed envelope shape, and rhus effect
interpolation among a series of waveforms. Actually, one could get the same
effect for as many segments as desired with just two oscillators by alternately
reassigning an oscillator's waveform table when its amplitude has cross-faded
to zero.
The availability ofsuch a high-quality, flexible synthesizer board set for
the Apple II inspired at least two companies to offer a music keyboard and
live-performance-oriented software to go with it. Alpha-Syntauri, for example,
manufactured a four-octave velocity-sensitive keyboard that plugged into
an interface board in another of the computer's expansion slots. Although the
6502 microprocessor only ran at half speed when the synthesizer was
operating, there was plenty of power remaining to scan the keyboard and
even update the display. Quite a lot of performance-oriented software similar
to that built into stand-alone keyboard synthesizers was offered for the
system. Additionally, an elaborate interactive graphics sound creation
program, reminiscent of the Fairlight eMl, was also oHered. Passport
Designs offered a similar setup initially with their own digitally controlled
analog synthesizer plug-in board. Later, however, they switched to the
Mountain synthesizer for its greater number of voices and flexibility.
Although both of these systems were quite popular with amateur and
semiprofessional musicians, the sound quality produced by 8-bit truncating
oscillators with 256-entry waveform tables was not quite up to professional
standards.