ARP 2600 - VCA Functionality in the Signal Path; Manual vs. Voltage Control of VCA Gain

60
out
5.108
Now
close
the
VCF-Mixer input
and open the
VCA-Mixer input.
Open the
VCF-VCA
input
and
raise
the
VCA initial
gain
to
maximum.
Feed any
audio
signal you
please into
the
filter; note that
with the
new
signal path
you
have set
up,
the signal you
are listening
has
passed
from
the
filter through
the
amplifier
before
going
into the mixer.
Close
the
VCA-Mixer
input and
open
the
VCF-Mixer input
again.
The
two signals should
be
identical:
the
maximum
output
level
from
the VCA is
no
higher
than
the level of its
input signal. Close
the
VCF-Filter
input
and
open the
VCA-Filter
input
once more,
and now
slowly
move
the
VCA
initial
gain
slider from
extreme right
to
extreme
left.
The
signal
is
slowly
attenuated
until
nothing
remains of it.
INITIAL
GAIN
slowly
We
mentioned briefly a
while back that if
you consider only
the manual
control of signal
amplitude that the VCA gives you, the
VCA could perfectly
well be
replaced
by
a
single
attenuator. You
have
just
seen how
this is
true; the
kind of control
you
have
over a
signal
by
means
of the
VCA
initial
gain slider
is
not different in any
way from
the kind of control you
have
by
means of say
the
mixer input attenua-
tors, or the
VCA's
two
signal input
attenuators themselves. The only
thing
that any
of them
can do is
lower the level of
a
signal passing
through.
From
beginning to
end, the patch you
are listening
to just
now
has
in
its
signal path a total
of
three attenuators (four if you
are
listen-
ing
to
the noise
generator) not
counting
the speaker volume controls.
But
of
course
the point
of the VCA's
presence
in
the 2600 is
not just to give you
one
more
manual
level control.
It is
to
give
you a
Voltage-Controlled
amplitude-governing
device. So
let's
control it with
a
voltage.