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VCO-
VOLTAGE
CONTROLLED
OSCILLATOR
The
VCO
is
the
primary
sound
source of
the
synthesizer
and
generates the basic
waveforms.
The
frequency
or
pitch
of these
waveforms
is
controlled
by
a
control
voltage.
SH-7
incorporates
two
independent
VCO's,
VCO-1
and
VCO-2.
VCO-1
produces
five
different
square
waves
of
2',
4', 8',
16',
and
32'.
This
feet-series
output
is
distinguished
as
VCO-1
(A).
VCO-1
(B)
is
exactly the
same
as
VCO-2.
When
a
chord
of
two
notes
is
played
on
the
keyboard,
VCO-1
(A,B)
produces
the higher
pitch
and
VCO-2
the
lower.
VCO CONTROL VOLTAGE
INPUTS
The most
important
control of
VCO
pitch
is
by means
of the
keyboard
control voltage
and
the
BENDER
control
voltage.
The
keyboard
control voltage
is
internally
connected
to the
VCO
through
the
KEY
MODE
switch.
The
BENDER
control voltage
is
connected through
the
BENDER
SENSITIVITY
controls.
Other
sources of control
voltage for control of
the
VCO
are:
the
LFO,
AUTOBEND
voltage,
and
the
S/H. Each
of these
may
be
fed to the
VCO
in
the
amounts
needed
to
produce
the
desired
effects.
Since
(A)
and
(B)
represent
two
parts
of the
same
VCO,
they
are
both con
trolled
by
the
same
set
of control voltage
inpu
sliders.
With
two
note performance,
it is
recommende
that
the input
levels
for
one
VCO
be
the
same
as
the
corresponding
effect for
the other
VCO.
1.LFO
This
slider
determines
the
depth
of control the
LFO
(Low
Frequency
Oscillator)
will
have
on
each
VCO.
It
can be used
for vibrato
effects,
and
for large
sweeping
pitch
changes.
2.
AUTOBEND
This control adds
a
change
of pitch
at
the
beginning
of
each note
played.
By
raising this
control,
the
VCO
pitch
is
controlled
by
a
y
shape
or
a
t
_
shape
voltage
envelope
so
that
the
sound
starts
with
a
lower
or higher
pitch.
When
the
Y"
shaped
bend
is
used,
the
human
voice, whistling,
and
other
sound
sources
which
begin
on
lower
pitches,
will
sound
more
real
and
natural.
When
the
K._.
shaped bend
is
employed,
chirping
sounds
of birds
can be
obtained.
3.
S/H
(SAMPLE
&
HOLD)
This
is
for controlling
VCO
pitch
with
the
S/H
output.
When
this
control
is
raised,
random
notes of
irregular
pitches
and
staircase
changes
of pitch for
arpeggio-like effects
can be
pro-
duced.
With
the
SH-7,
the
envelope generator
can be
triggered
with changes
in
the
pitches
produced by
the S/H. Set the
KEY
MODE
switch
(see
page
8)
to
EXT
CV/GATE/IS/H)
to
trigger
the envelope generator with the
S/H
clock
pulses.
For
this
mode
of operation, there
should be
no
connection
to the
GATE
INPUT
jack,
otherwise
the
envelope generator
will
be
triggered
from
the
external source.
4.
AUTOBEND
TIME
This controls the time required
for the
VCO
to
return
to
its
normal
pitch
when
using the
AUTOBEND.
Turning
the
knob
clockwise
increases
the time.
Normally,
this
control
is
set
between
and
5; special effects
are
obtained
with
higher
settings.
5.
POLARITY
This
switch
changes
the
autobend
polarity.
VCO-2
The
sound
will start
with
a
higher
pitch
when
set
to the
Jv_
position
and
a
lower
pitch
at
the
y
position.
The
K_
shape bend
is
normally
used.
The
V
shape
bend
is
used
for
special effects
like
chirping of
birds.
6.
VCO-2
TUNING
This control
is
for
the tuning of
VCO-2
only
and
is
used
to
match
the pitches of
VCO-2
to
VCO-1;
or
for
purposely
mistuning,
or
to
produce
tunings
of
musical
intervals.
The
range
of
this
control
is
±700
cents
(700
cents
=
perfect
fifth), or,
with
C
as
the
center,
from
the
F below
to
the
G
above.
7.
SYNC
SWITCH
Turning
this
switch
ON
will
lock the
frequency
of
VCO-2
to that of
VCO-1
so
as
to
completely
eliminate
beat
frequencies
caused
by
slight
mistuning. Besides unison, the
VCO
frequencies
will
lock
at
various octave
intervals
also.
Since
other
intervals
become
impossible,
the
two
voice
feature
of
the
keyboard
is
no
longer
operable.
8.
VCO-1
(A)
FEET
SERIES
MIXER
The
(A)
portion
of
VCO-1
simultaneously
produces
five
square
waves
which
can be
mixed
together
in
any
desired
ratio.
As
shown
in
the
drawing on
the
right,
when
the synthesizer
is
set
to
produce
the pitch
of
middle
C,
the
square
waves produce
pitches
one and
two
octaves
above and below middle
C.
Interesting
sounds can be produced by mixing
the
2'
output
with the
8'
output, or the
2'
output
with
the 16' output.
The
2'
+
8'
com-
bination
produces
a
vibraphone-like
sound.
Using
all
of
the outputs together
produces
very
large
full
sounds.
Raising
and
lowering these
controls
has
no
effect
on
the
total
sound
level
at
the
output
of
the synthesizer; the
sound
level will
remain
the
same whether one
or
all
the controls are
raised.
2'
f
IZE
^
-JUUU1T
-juu
-&-
16'
32'
2'
—
8'
mixed.
9
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