About the Prophet-600
Early
in 197S Sequential Circuits
revolutionized the art of keyboard synthesis by
introducing the
Prophet-5, a compact instrument intended for the performer. Before
the Prophet
appeared it was not possible for a keyboardist to
instantly
select
custom
synthesized sounds
and
play them
polyphonically. Its featured programmability used
emerging
microcomputer technology to
allow
complete
and instantaneous control over,
essentially,
five complete synthesizers
(voices). The Prophet-5 became the leading
instrument of its kind.
Now
technology has developed to the point
where SCI can offer the six-voice Prophet-
600,
which sounds basically like a
Prophet-5,
at
less than half its price. It has the
capacity for 100
sound programs. All programs can be fully
customized (edited) and
stored internally, or on audio tape
via
the
built-in cassette interface. The Prophet-600
adds a flexible arpeggiator and a
**00-note, real-time polyphonic sequencer, which
remembers whatever you play.
The
Prophet-600 actually contains six individual synthesizers, termed "voices." For its
principle sound sources, each voice contains two
voltage-controlled
oscillators (VCOs),
referred
to as
OSC A and OSC B. OSC A and OSC B can be mixed into a resonant low-
pass voltage-controlled filter
(VCF).
The filter
modifies the voice timbre under control
of
its four-stage envelope generator. The filter may also
serve
as a
sound source.
Following each filter, a voltage-controlled amplifier (VCA)—also controlled by a four-
stage
envelope generator—shapes the voice amplitude. Only one voice is depicted on
the control panel, because the voice controls "patch" the six voices
identically.
This
makes the
voices homophonous—they
sound
alike—with pitch differences corresponding
to (at most) six simultaneously-held keys.
Supplementing the basic voice are polyphonic modulation (POLY-MOD) signal
routings
within each voice that allow OSC B and the filter envelope generator
to
function
as
modulation sources applied
to OSC A or the filter cutoff frequency. There is a single
low-frequency oscillator (LFO) which can modulate all
six
voices
to a depth adjusted
by the
modulation (MOD) wheel. The PITCH wheel can
be used to raise or lower the
pitch of all voices by the same interval.
The term "digital-analog hybrid" is often used to describe the Prophet synthesizers.
This means that rather than directly controlling,
the
analog
synthesizer
voices,
the
keyboard
and most controls are actually devices which input
"data" to a
microcompu-
ter
system which in turn "programs"
the
voices.
This microcomputer system has
several important functions. It solves the problem of generating six independent sets
of
voice control voltages
and gate signals
(which
operate the envelope generators)
from
a
single keyboard. In
fact, in
the
Prophet-600
the
(formerly)
analog envelope
generators and LFO
have
been entirely replaced by computer system functions. The
digital memory
provides
a way to store all of the switch and knob settings which form
a program,
and the keystrokes which
form sequences. The programs and sequences are
retained even when the Prophet is turned off, thanks to a small battery with a 1 0-year
life. Finally, the microcomputer system keeps
the
twelve voice
oscillators in tune.
CM600A 12/82
in
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