ARP 2600 - Page 77

72
Filter Frequency
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USING THE
ADSR
ENVELOPE VOLTAGE
TO
CONTROL
THE VOLTAGE
CONTROLLED FILTER.
Follow
the
same
plan
of
attack
here that
you
used
with the
VCA, using
first a pink-noise
source
and
then
one
of the
VCO's.
Feed
the VCF
output directly
to the Mixer; the point of our
first
exercise
here will be
to
demonstrate that the
VCF
can
create
an
event
all by
itself,
without
the help of the VCA.
To
do this we will
make use of the
fact
that when the
filter
initial
frequency control is at
minimum, the filter
F
c
is
so low
that
the
filter
will not
pass
any
audio-frequency signals.
So
set
the initial
frequency slider
all
the
way to
the
left.
Open the
NG-Filter
input
all
the way
and open
the
VCF-Mixer input.
Open
the
ADSR-Filter
control input all
the
way.
Set
the
ADSR
envelope generator controls
for
a
percussive
short-duration envelope—say minimum attack,
the
initial
decay
about
halfway
up,
minimum sustain level and
final
release.
Jab
the manual start
button
a
few
times or
use
the keyboard
gate
by
pressing
a
key.
Compare this
envelope with
the
one that
results from
feeding
the same
ADSR output
and
noise into
the
VCA,
Raise the
sustain
level about halfway
and
make the compari-
son
again. (The simplest way
to make a
quick patch for
purposes
of
comparison
is to
take
a
patch
cord
and
connect
the
NG
output
directly
to
one
of
the VCA
signal
inputs;
open that
input
attenuator
and
the
one
over
the
ADSR
Amplifier
control input; now you
can
simply alternate
between
the
two
mixer
inputs
to
hear
first
the
VCF
output and
then
the
VCA output.)
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