Roland SH-09 - Voltage Controlled Filter Operation

The Audio
Mixer also
contains
a slider controlling
the
amount of input accepted
from
any electronic
instrument
signal
inserted
into
the External Audio In
jack on the
back
panel of the SH-09. The SH-09
12
may
be
used
in
several
different
ways
to
process
external
instruments
(in
contrast
to processing
its
own
VCO
signal),
and
these are
discussed in
this
manuals
Interfacing
section.
Voltage
Controlled
Filter
The
basic
VCO sound
now
passes automatically
from
the
Audio Mixer on through the
Voltage Con-
trolled
Filter
(VCF). Here
the tone resulting from
choices
made within
the
VCO and
Audio Mixer
may
be finely
adjusted and
manipulated.
The
basic
patch passes
the VCO
sound
directly
through
the VCF unchanged,
opened
by raising the
Cutoff
Frequency
slider
fully. An
understanding
of
the
effect of
the filter
Cutoff
is basic
to
an
unders-
tanding
of
the entire
VCF
section.
The SH-09
VCF
is a
high
quality Low Pass
Filter.
With
the Filter Cutoff slider
set at
'10',
it
has no
effect
on the
sound.
As this slider
is lowered,
the
tone
becomes progressively more mellow
as the
higher
parts of the tone are removed,
becoming
a
pure
sine tone
just before
it
is filtered away
to
silence.
Lower and raise this
slider at different
speeds using
each basic waveform from
the
VCO
to obtain
an aural
picture of the various
colors
available
and
also
of
the effect of
motion within
the
filter.
Motion
within
the filter, changing
the tone
during
musical
notes, is
critical to many
synthesizer
sounds.
Some
synthesized
sounds are
based on
a
'passive' filter,
a
fixed
Cutoff Frequency
setting with
no motion
or
change in tone. Others
depend on the
tone
changing
'actively' during
the length
of each
note,
either
a repeating
change controlled
by the
LFO
Modulator or
a
single sweep
initiated
by the
Envelope
control. The most
basic
demonstration
would
be to compare
the basic brass
and
string
patches
presented
in this manuals
section on
Patches.
The prime
difference
between
these two
sounds is
the 'passive' filter of
the string
patch
as
contrasted
to the 'active' filter
of the
brass
patch.
Move
the Cutoff Frequency
slider
to
'1
0'
while
its
selector
is
in
the middle, ENV
(positive envelope),
positioa
Press
any key and the note will
change
both in volume
and
tone
according
to
the shape
set in the ENV
section of our
basic
patch, getting
brighter
and louder,
then more mellow
and soft
The
volume level
followes the
tone
just as it did
when
the slider was
manually moved.
This experi-
ment
moves
the
filter
exactly
the way it
could
be
done manually,
but
with more
potential
speed, pre-
cision
and
ease
through
automatic
control.
Repeat
this procedure
with different
waveforms
and
different
amounts of VCF
Envelope
Control.
Return
the Cutoff
Frequency slider
to
'10',
move the
selector
to
EMV (inverted
envelope)
and
move the VCF
Envelope Control
to
'6'.
Your effect
is now
reversed, closing
the filter
rather than
open-
ing
it
moving
this
time
from
bright and
loud
to
mellow and less
loud and
back again
each time
a
key
is pressed. This
inverted
envelope is very
use-
ful in creating
plucked or
strong, punching
syn-
thesizer sounds with
lots of
dynamic motion.
Experiment
here with
different
waveforms
and
different Cutoff
Frequency
starting
points and
amounts of Envelope
Modulation.
Patches are
given later for
specific
applications
of
this
feature.
The ENV FOL'R
position
on
the three
position
VCF
Envelope
Mode Selector
uses the natural
shape of
notes introduced
at
the
External
Audio In
to move
the filter, allowing
instruments
such
as electric
piano or
electric guitar with
no
Gate
Voltage
out-
puts to drive the SH-09.
Specifics
on
this pro-
cedure
are
given in
the Interfacing
section of
this
manual.
The MOD slider within
the VCF
section
allows
you
to change
the
tone of
your note
with
the
IFO
Modulator.
Begin with your
basic
patch, lower
the
Cutoff Frequency
slightly
to
7',
and
gradually raise
the MOD
slider. You will
hear
a
tone/volume tre-
molo
(the speed and shape
are
determined
again
in the Modulator
section),
the
depth of
tremolo
varying with
the MOD slider
position. It
is useful
to
note here
that the tremolo
is
smoothly,
alternately
both raising and
lowering
the Cutoff
Frequency
(for
brighter
and more mellow
tone,
respectively). For
this
reason the Cutoff
Frequency
slider
has
been
lowered slightly
to make room
for
both
actions. If
the Cutoff
Frequency
slider was
in either
extreme
position,
any tremolo
would
lose its
smoothness
as
only half of
its cycle
could have
any
influence
on
what
is heard.
Experiment
with
this now
and later
check
the Vibraphone
patch for
a specific
exam-
ple.
The
Resonance slider in
the VCF
section
emphas-
izes the tone
at
the
precise
edge of
the Cutoff Fre-
quency. Place
the Cutoff
Frequency
slider
at any
point
that allows
a tone
to pass, then
add any-
where from
'0'
to
'6'
of
the
Resonance
slider
and
you
will
hear
a slight difference
in tone.
Leave
the
Resonance
slider
at
'6'
and
move
the Cutoff Fre-
quency
slider.
Resonance
emphasizes
the
edge
of
the Cutoff
and when
it is
moved the
motion
is
emphasized. The
prime
use
of
Resonance
is
to
emphasize
tone in motion,
such
as
the
twang of
the
bass guitar
in the
Shuffle
Bass
patch given
later in
this
manual. You
may wish
to leave
the
Resonance
slider
at
'6'
or less
and
repeat the
experiments
with
Envelope or
LFO Modulation
of
the VCF
to
learn
how
these
automatic
changes in
tone are
emphasized using
Resonance.
Once
that is
completed,
push
the Resonance
slider
fully
to
'10',
and again
move the Cutoff
Frequency
slider.
You will
now hear
an extra
pitch in addition
to that produced
by
the
VCO, one
whose
pitch is
determined
by
the
VCF
Cutoff
point
Silence
the
VCO
at the Audio
Mixer
and experiment
with
various
kinds of
modulation
using
the
Resonance
as
an
extra
oscillator
—
all functions
which altered
the tone using
the VCF
will now
move
the pitch of
the VCF
produced note in
the same
manner.
This
use of
the
Resonance
as an extra
oscillator
may
be