Part
B:
Specific
Applications
This
part of
the manual provides very specific
instructions
and suggestions on
how
to
use
the 622
in
the fields
of
Sound Reinforcement, Recording Studios, Motion
Picture Sound, Broadcasting, Dance Bars, and provides comments on Electronic
Music.
We recommend that
anyone involved in pro
audio
(and certainly those
involved in its more eclectic aspects, such as
Theater)
read all
the
sections.
The
applications information
in each
will undoubtedly provide much food for thought.
I: STEREO For
broadband equalization
(BANDWIDTH
controls
at or clockwise of
"5"),
no
difficulty
should result when
the channels are matched
on the basis
of panel
calibrations
alone.
In
applications other than
monitor
tuning or sound reinforcement,
however,
if any
BANDWIDTH
control is
adjusted "narrowband"
(i.e., 0 through
5),
then
test
instruments should
be used to
assure matching between
stereo channels,
assuring precise
stereo imaging
and accurate mono
summing of the channels. (See
the
section on
Dance Bars below for
a discussion of
matching requirements in
monitor
tuning and reinforcement
applications.)
The
following
procedure assumes that both channels
have been adjusted
by ear to
achieve the
desired equalization,
and that both are adjusted
identically with
reference
to panel calibrations.
One channel must
be arbitrarily chosen
as
the
"reference",
and the other
channel's controls
must then be slightly
tweaked to
achieve
a precise
instrument-match
to
this
reference.
This
is most readily done by
the
"differential
method": the
reference channel and the
channel
under adjustment
are
swept
out-of-phase,
and their outputs are
summed. The channel
under
adjustment
is tweaked
to minimize the amplitude
of the
sum.
This method
is
very
sensitive
because
it automatically indicates both
phase and amplitude
mismatches.
It
is performed
as
follows:
1) Connect
a sinewave sweep generator
with logarithmic sweep
to the input of
the
reference
channel such that the hot output
is connected
to the
reference
channel's
(+)
input, and its (-) input
is grounded.
2)
Connect
another output from the sweep
generator
to
the
channel
under
adjustment. Connect the
hot
output
to this channel's
(-)
input; ground
its
(+)
input.
3)
Sum
the outputs of the
two
channels by connecting each
(+)
output to
one
side
of a 22K 5% 1/4 watt carbon resistor (the value is
not
particularly
critical). Connect
the other side of both resistors to the vertical input
of
an
oscilloscope.
4)
Sweep
the channels from 20-20,000Hz,
and adjust the
scope
sensitivity
to
easily
see the swept component.
5)
Switch
aU
IN/OUT
switches on
both channels OUT. Adjust
the
GAIN control
on the channel
under
adjustment
to
null the
output observed on
the
scope.
6)
Switch
all
IN/OUT
switches
IN
(unless
some
of
these switches
are
normally
out on the
reference
channel).
7)
Slightly
adjust
the various controls on the channel under adjustment to
minimize the amplitude of the differential component as observed
on
the
scope.
8
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