41
VOUTAOrE PROCESSOR.
(iNVCHrtR)
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4.5
The
VOLTAGE
PROCESSOR
section
of the
2600
contains
three
separate
processors.
Two are mixing and inverting
processors and
the
third produces
a variable
lag.
4.51
The
first
processor
accepts up to four inputs in
the
range
from
DC
through
20KHz
and
produces an output
voltage
of opposite
polar-
ity
from that
represented
by
the
instantaneous sum
of
the
input
vol-
tages.
Thus
for example
the keyboard voltage, which normally
goes
from
0V
to +4V, if
run
through the inverting processor would
go from
0V
to
—
4V
and
would therefore
drive
the
frequency of an
oscillator
down
from left
to right
on the keyboard. Positive-going envelopes
become
negative-going
envelopes,
etc.
This inversion,
applied to audio
signals, puts them
exactly
180°
out of phase with
their
uninverted form. Such phase
inversion
has
absolutely
no
audible effect unless an inverted
signal
is
in some form
mixed
with
its
uninverted
counterpart, in
which case the signals mixed
will
partially
or
entirely
vanish.
m
~
Two
of the
inputs to the
first
inverting
processor are-attenua-
tor governed
and two are
not.
The inverter has one output.
4.52 The second inverting processor is exactly
the
same
as
the
first
except that it has only
two
inputs, one attenuator-governed and one
unattenuated.
4.53
The LAG PROCESSOR acts only on
sudden changes
in
the input
voltage presented to
it. It slows them down by
an
amount
controlled
with
the slider in the signal path.
With
this
control set
at
maximum,
the time
required for the
output
voltage
to
reach
a
value suddenly
assumed
by the input voltage is at most about
.5
sec. With
the control
at
minimum the
amount
of
time
required
is at most
about
5
ten-thous-
adnthsofa
second. This minimum lag has no audible
effect when
the
signal
being processed
is a
control
signal of
low frequency,
but it
is
there nonetheless:
audio-frequency
signals
will be
filtered
sharply
above
1
600Hz
by even the minimum
rag
time
of
the processor.
The
time constants
strictly
defined
depend
somewhat oh
the output
imped-
ance of
the signal source; for
a 1
Kohm source impedance they are
.1
ms
minimum and .Isec maximum.
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