Roland SH-1 - Internal Components

VCA
-
VOLTAGE
CONTROLLED
AMPLIFIER
VCA
(VOLTAGE
CONTROLLED
AMPLIFIER)
The
VCA
is
an
amplifier
whose
gain is
controlled
by a
control
voltage. In
other
words,
the
varying
control
voltage
acts
much like a
volume
control to
any
sound
passing
through
the
VCA.
If the
output
of
the
envelope
generator is
used to
control
the
VCA, then
the
sound
passing
through
the
VCA
wili take
on a
loudness
pattern
corresponding
to the
shape
of the
envelope
voltage.
1.
ENVELOPE
SWITCH
(ENV-1/ENV-2)
This
switch
decides
which
of the
two
envelope
generators
will
control
the
VCA.
At
ENV-1, the
envelope
used
for
control
of
the
VCF is also
used
for the
control
of
the
VCA.
Normally
this is set
at
ENV-1,
which
has
A
(attack), D
(decay), S
(sustain),
and
R
(release)
controls.
The
ENV-2
has
A
(attack) and
R
(release)
controls
only
and
is
convenient
for
synthesizing
con-
tinuous
sounds like
the
violin and
organ.
When
controlling the
VCA by
an
envelope
separately
from
the
VCF (for
brass
instru-
ments,
for
example),
use
ENV-2.
2.
HOLD
CONTROL
When
there
is no
envelope,
the
VCA is
"closed"
and
will not
pass
sounds.
Raising
the
HOLD
control
will
"open"
the
VCA to
let
sounds
through. It is
most
often
used
when
it is
desirable to
control
the
sound
envelope
entirely by
means
of
the
VCF,
or when
tuning the
synthesizer,
or
when
processing
external
sound
sources.
When
controlling the
VCA
with an
envelope,
set the
HOLD
slider at
"0".
If the
HOLD
slider is
raised, the
volume
of
sound
cannot
be
controlled
by
the
envelope
as
shown
at the
right.
With the
HOLD
slider
at
"10",
the
VCA is
completely
"open"
and
sound is
produced at
a
constant
volume.
FUNCTION
OF
VCA
HOLD
FUNCTION
OF
HOLD
HOLD
A
at
maximum
j
tu
D
.:/,J. .V
"'-'
wmm
mm
%w
i
m
HOLD
at
middle
HOLD
at
minimum