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HIGH PASS
FILTER
Before entering the
VCF,
the
signals
mixed
in
the
AUDIO MIXER
pass
through
the
HPF
(High
Pass
Filter).
The
HPF
blocks
low
frequen-
cies
and
passes high frequencies.
With
the
CUTOFF FREQ
control
at
its
lowest
position,
all
sounds
pass
through
the
HPF
without change;
this
may
be thought
of
as
its
normal
position.
When
the
CUTOFF FREQ
control
is
raised,
the
HPF
will
remove
the
lower
harmonics
from
the
sound
source, thus
brightening the
sound.
It
is
normal
for
higher
positions
of
this
control
to
produce
lower
levels
of
output sound; compensate
for
this
by
raising
the
TOTAL
VOLUME
control.
The
HPF
can be used
for synthesizing
harpsi-
chord and
oboe
sounds,
for
example.
HPF
VCF -VOLTAGE CONTROLLED
FILTER
The
VCF
is
a
low
pass
filter
whose
cutoff
frequency
(or
filtering characteristics)
can be
controlled
by
means
of
a
control
voltage.
The
VCF,
being
a
low
pass
filter,
acts
in
a
way
opposite
to
that
of the
HFP.
It
passes
low
frequencies
and
blocks
high frequencies.
1.
CUTOFF FREQ CONTROL
This control
determines
the frequencies
which
will
be
removed by
the
VCF.
At
its
highest
position,
all
sound
passes
through
the
VCF
without change, thus
this
may
be considered
its
normal
position.
If
the control
is
slowly
lowered,
it
will
begin
to
shave
off
the
upper
harmonics
of
the
sound
passing
through
the
VCF.
In
its
lowest
position,
the
VCF
CUTOFF
FREQ
control
will
remove
all
frequencies so
that the
VCF
blocks
all
sound.
NOTE:
If
the synthesizer
produces
no
sound,
this
is
one
of the
first
things
you
should check.
2.
RESONANCE CONTROL
This control accents the frequencies
at
the cutoff
point
of
the
VCF.
At
"0", the
RESONANCE
control has
no
effect.
The
effect
will
become
stronger the higher the control
is
raised.
At
about
"8", the frequencies
at
the cutoff point
are
accented
so strongly
that the
VCF
starts
to
oscillate
by
itself,
or
in
other words,
it
begins generating
a
sine
wave
even with
no
input
to
the
VCF. The
frequency
of
this
sine
wave
will
depend
on
the position of the
VCF
CUTOFF FREQ
control.
•
The
VCF
CUTOFF FREQ
control
gives
manual
control over the cutoff
frequency point
of the
VCF. The
following
group
of controls
allows the cutoff
frequency
to
be
controlled
by means
of control
voltages.
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