Universal Audio 535 User manual

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Murn
□
model
535
DUAL GRAPHIC EQUALIZER
model
533
GRAPHIC EQUALIZER
UNITED
RECORDING
ELECTRONICS
INDUSTRIES
8460
SAN
FERNANDO
RD
..
SUN
VALLEY
.
CALIFORNIA
91352
(818)
767
-
1000
.
M[re
~

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BEFORE
PROCEEDING
WITH
COMPLETE UNPACKING AND
SETUP,
CONSULT UNPACKING AND INSPECTION INSTRUCTIONS
ON
PAGE
4
model
535
DUAL GRAPHIC EQUALIZER
model
533
GRAPHIC EQUALIZER
United
Recording
Electronics
Industries
8460
SAN
FERNANDO
ROAD,
SUN
VALLEY,
CALIFORNIA
91352
(818)
787-
.
1000
Printed
in U.S.A.
©
Copyright
1979,
UREI

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TABLE
OF
CONTENTS
SECTION
I.
INTRODUCTION
1.1
.
DESCRIPTION
1.2
SPECIFICA~IONS
1.3
CONTROLS
SECTION
II.
INSPECTION
AND
INSTALLATION
2.1
UNPACKING
AND
INSPECTION
2.2
ENVIRONMENTAL CONSIDERATIONS
2.3
POWERING
2.4
LINE
VOLTAGE
SWITCH
2.5
EXTERNAL CONNECTIONS
2.5.1
MODEL
301
XLR/QG ADAPTER
2.6
IMPEDANCE
AND
TERMINATION
2.7
SIGNAL LEVEL
AND
OVERLOAD
DETECTOR
2.8
ACCESSORIES
2.9
RACK
MOUNTING
A
MODEL
533
2.10
RACK
MOUNTING
TWO
UNITS
(MODEL
533)
SECTION
Ill.
OPERATING INSTRUCTIONS
3.1
GENERAL
3.2
SYSTEM
CHECK
3.3
EXPERIMENTATIO~
3.4
DOCUMENTATION
3.5
APPLICATION
3.5.1
OBJECTIVE
MEASUREMENTS
VS
SUBJECTIVE
HEARING
3.5.2
ADDITIONAL
HINTS
3.5.3
SPECTRAL
DISTRIBUTION
IN
THE
AUDIO SIGNAL
3.5.4
EQ
SYSTEMS
AND
LIMITERS
3.6
DISCUSSION
OF
EQUALIZATION
3.6.1
BEFORE EQUALIZATION
3.6.2
MEASUREMENT
TECHNIQUES
3.6.3
ADJUSTMENT
OF
EQUALIZERS
3.6.4
SOME
PROBLEMS
WITH
CORRECTIVE
ROOM
EQ
3.6.5
FEEDBACK
~UPPRESSION
3.7
GAIN STRUCTURE
AHD
SIGNAL-TO-NOISE
3.8
INPUT LEVEL
3.9
OVERLOAD
INDICATOR
SECTION
IV.
THEORY
OF
OPERATION
4.1
GENERAL
4.2
INPUT
AMPLIFIER
4.3
GAIN
AMPLIFIER
4.4
GRAPHIC EQUALIZER
4.4.1
GENERAL
4.4.2
FILTERS
PAGE
1
2
3
4
4
4
5
5
6A
7
8
8
8
9
11
11
11
-
11
11
13
13
14
14
15
17
18
19
19
20
21
22
22
23
23
23
23
23
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TABLE
OF
CONTENTS
4.4.3
THE
ACTIVE INDUCTOR
4.5
OUTPUT
AMPLIFIER
4.6
OVERLOAD
INDICATOH
4.7
POWER
SUPPLY
SECTION V.
MAINTENANCE
5.1
GENERAL
5.2
REPAIRS
AND
WARRANTY
5.3
SERVICE ADJUSTMENTS
5.3.1
COMMON
MODE
BALANCE
5.3.2
OFFSET ADJUSTMENT
5.4
CLEANING
5.5
ON
OP
AMPS
SECTION
VI.
ILLUSTRATION
SCHEMATIC
DIAGRAM
OF
UREI
MODEL
SCHEMATIC
DIAGRAM
OF
UREI
MODEL
(Continued)
PAGE
25
26
26
26
27
27
27
27
28
28
29
533
535

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; .
SECTION I
INTRODUCTION
Bffll
FIGURE
1.
MODEL
535
FRONT
PANEL.
NOTE:
This
manual
contains
complete
instructions
for
the
operation
of
the
two-channel
"Dual
Graphic
Equalizer"
Model
535.
However,
this
manual
is
also
intended
for
the
single
channel
"Graphic
Equalizer"
Model
533.
If
used
with
a
Model
533,
all
references
to
the
two-channel
unit
should
be
disregarded.
1.1
DESCRIPTION
The
Model
535
Dual
Graphic
Equalizer
is
a
studio
quality
product
which
has
wide
application
in
recording,
sound
reinforcement,
radio
and
TV
production,
and
high
fidelity
music
systems.
The
system
is
designed
to
operate
at
any
nominal
level
from
as
low
as
-20
dB
(Ref.
0.775
V)
allowing
its
use
with
low
level
mixers,
high
or
low
impedances,
and
balanced
or
single-ended
circuits.
The
Model
535
provides
12
dB
of
boost
or
cut
at
each
of
its
10
frequencies
which
are
centered
at
ISO
!-octave
increments
from
31.5
Hz
to
16
kHz.
The
positions
of
the
control
arms
of
the
vertical,
stepless
controls
provide
a
graphic
representation
of
the
response
curve
selected.
The
filters
are
active,
minimum
phase,
2-pole
synthesized
LC
networks,
whose
skirts
properly
combine
for
minimum
ripple
and
phase
shift
when
used
in
combination.
A
front
panel
control
adjusts
the
gain
from
-10
dB
to
+20
dB.
Bypass
switches
permit
switching
the
equalization
out
for
A-B
tests.
An
optional
(SC-1)
security
cover
may
be
installed
to
protect
all
operating
controls
against
inadvertent
disturbance
or
tampering
in
fixed
installations.
-1-

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l.
✓•
SPECIFICATIONS
ELECTRICAL
(EACH
CHANNEL):
INPUT:
Balanced
bridging,
differential
amplifier.
INPUT IMPEDANCE: 40
kohms,
used
as
balanced
input.
20
kohms,
used
as
unbalanced
(single-ended)
input.
MAXIMUM
INPUT LEVEL:
+20
dB
(7.75
volts).
EQUIVALENT
INPUT NOISE:
Less
than
-90
dBm.
15.7
kHz
noise
bandwidth
with
all
controls
set
flat,
output
termina-
ted
with
600
ohm
load
(Model
535,
-88
dBm).
GAIN:
Variable,
-10
dB
to
+20
dB,
with
front
panel
control.
FREQUENCY
RESPONSE:
±1
dB,
20-20,000
Hz
(with
no
EQ).
OUTPUT:
Floating,
transformer
isolated.
OUTPUT
LOAD:
150
ohms
or
greater.
POWER
OUTPUT:
+24
dBm
into
600
ohm
load
(12.28
volts),
+20
dB
into
150
ohm
load
(7.75
volts).
DISTORTION:
Less
than
0.25%
THD, 30
Hz
to
15
kHz
at
maximum
rated
output.
FILTER TYPE:
2-pole
synthesized
L-C.
FILTER
BANDWIDTH:
1-octave
at
-3
dB
points
with
8 dB
boost
or
cut.
CENTER
FREQUENCIES:
Standard
ISO
(Hz)
31.5
63
125
250
500
lk
2k
4k
Bk
16k.
FREQUENCY
ACCURACY:
RANGE
OF
BOOST
AND
CUT:
CALIBRATION
OF
BOOST
AND
CUT:
CHANNEL
SEPARATION:
MISCELLANEOUS:
POWER
REQUIREMENTS:
±3%
of
center
frequency.
12
dB,
single
filter
section.
Within
1 dB
of
indicated
setting,
Oto
±6
dB,
within
1.5
dB
of
indicated
setting,
±6
to
±12
dB,
(single
filter
section).
60 dB
worst
case
at
high
frequencies,
typically
better
than
80
dB.
100-125
VAC
or
200-250
VAC,
50/60
Hz,
switch
selectable,
less
than
10
w.
-2-

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ENVIRONMENT:
Operating
0°C
to
+50°C
(+32°F
to
+122°F);
storage
-20°C
to
+60°C
(-4°F
to
+140°F).
CONNECTIONS:
Input
and
output,
through
rear
chassis
barrier
strip,
or
XLR/QG
connectors
through
Model
301
accessory
adapter;
Power
through
3-wire
power
cable;
Model
533
utilizes
IEC
style
connector
and
power
cord.
(See
Installation
Instructions,
Section
2.5.)
PHYSICAL CHARACTERISTICS:
DIMENSIONS:
Model
535,
483
x
89
mm
rack
panel;
depth
behind
panel
203
mm.
(19"
x
3-1/2"
x
8");
Model
533,
216
x
89
mm
rack
panel;
depth
behind
panel
190
mm
(8-1/2"
x
3-1/2"
x
7-1/2").
FINISH:
Panel
is
3.18
mm
(1/8")
brushed
clear
anodized
aluminum,
in
two
shades.
Chassis
is
cadmium
plated
steel.
WEIGHT:
Model
535,
4.31
kg
(9.5
pounds);
Model
533,
2.95
kg
(6.5
pounds).
SHIPPING
WEIGHT:
Model
535,
6.35
kg
(14
pounds);
Model
533,
4.08
kg
(9
pounds).
ACCESSORIES:
Model
SC-1
Security
Cover,
smoke
gray
transparent
plastic;
covers
all
operating
controls
(Model
535
only).
1.3
CONTROLS:
Model
301
XLR/QG
adapter;
two
needed
for
Model
535.
One
adapter
provides
connec-
tions
for
signal
input
and
output.
EQUALIZATION:
Vertical
slide
controls,
continuously
variable
Oto
±12
dB.
GAIN:
Screwdriver
adjustable
from
-10
dB
to
+20
dB.
EQ
IN/OUT:
Front
panel
toggle
switch.
POWER:
Front
panel
toggle
switch.
INDICATORS: LED,
Power
ON;
LED,
Overload
Condition,
levels
monitored
at
3
circuit
points;
MAINS
VOLTAGE:
Rear
panel
slide
switch,
115/230
volts.
-3-

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SECTION
II
INSPECTION
AND
INSTALLATION
2.1
UNPACKING
AND
INSPECTION
Your
Model
535
was
carefully
packed
at
the
factory,
and
the
container
was
designed
to
protect
the
unit
from
rough
handling.
Nevertheless,
we
recommend
careful
examination
of
the
shipping
carton
and
its
contents
for
any
sign
of
physical
damage
which
could
have
occurred
in
transit.
If
damage
is
evident,
do
not
destroy
any
of
the
packing
mater-
ial
or
the
carton,
and
immediately
notify
the
carrier
of
a
possible
claim
for
damage.
Shipping
claims
must
be
made
by
the
consignee.
'
The
shipment
should
include:
Model
535
Dual
Graphic
Equalizer
UREI
Instruction
Manual
(this
book)
Two-part
Warranty
Card
bearing
the
same
serial
number
as
the
Model
535.
Mounting
screws
and
finish
washers
(for
rack
mounting
of
535
only).
2.2
ENVIRONMENTAL
CONSIDERATIONS
The
system
will
operate
satisfactorily
over
a
range
of
ambient
temperatures
from
0°C
to
+50°C
(+32°F
to
122°F),
and
up
to
80
%
relative
humidity.
If
the
system
is
installed
in
an
equipment
rack
together
with
high
heat
producing
equipment
(such
as
power
amplifiers),
adequate
ventilation
should
be
provided
to
prolong
the
life
of
components.
Also,
while
circuitry
susceptible
to
hum
pick-up
is
sufficiently
shielded
from
moderate
electromagnetic
fields,
installation
should
be
planned
to
avoid
mounting
the
system
immediately
adjacent
to
large
power
transformers,
motors,
etc.
2.3
POWERING
The
535
may
be
operated
from
either
100-125
VAC
or
200-250
VAC
mains
(50
or
60
Hz,
single
phase.)
As
indicated
in
Section
2.4,
the
nominal
line
voltage
may
be
selected
with
a
rear
panel
switch.
BE
SURE
TO
VERIFY
BOTH
THE
ACTUAL
LINE VOLTAGE,
AND
THE
SETTING
OF
THE
VOLTAGE
SELECTOR
SWITCH
BEFORE
CONNECTING
THE
535
TO
THE
MAINS.
-4-

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To
comply
with
most
Electrical
Codes,
the
535
is
supplied
with
a
three-wire
AC
cord,
the
grounding
pin
of
which
is
connected
to
the
chassis.
In
some
installations
this
may
create
ground-loop
problems.
Ground
loops
can
become
very
evident
(as
hum
and
buzz)
if
a
significant
potential
difference
exists
between
the
AC
conduit
ground
and
the
~rounded
metal
enclosure
in
which
the
chassis
is
installed.
If
hum
is
experienced,
check
for
the
possibility
of
ground
loops
by
using
a
3-prong
to
2-prong
AC
adapter,
ungrounding
the
AC
plug
temporarily.
This
ungrounds
the
Model
535,
and
will
probably
cure
the
hum
or
buzz,
but
is
not
a
substitute
for
proper
system
grounding.
Be
aware
that
unless
the
Model
535
Dual
Graphic
Equalizer
is
AC
grounded,
a
safety
hazard
can
exist.
UREI
accepts
no
responsibility
for
legal
actions
or
for
direct,
incidental
or
consequential
damages
that
may
result
from
violation
of
any
electrical
codes.
2.4
LINE
VOLTAGE
SWITCH
Unless
a
tag
on
the
line
cord
specifies
otherwise,
the
Model
535
was
shipped
ready
for
operation
with
nominal
115
VAC
power
mains.
In
order
to
change
this
for
nominal
230
V
(50
or
60
Hz),
slide
the
VOLTAGE
SELECTOR
switch
on
the
rear
panel
to
the
230
position.
The
voltage
is
visible
in
a
window
next
to
the
switch
slot.
Be
sure
to
change
the
fuse
to
the
correct
value:
1/8-amp
slo-blo
when
changing
to
230
V
operation
or
1/4-amp
slo-blo
for
115
V
operation.
A
small
screwdriver
should
be
used
to
move
the
recessed
switch.
2.5
EXTERNAL
CONNECTIONS
Permanent
input
and
output
signal
wires
should
be
shielded
cable,
and
connected
in
accordance
with
standard
wiring
practice,
as
indicated
on
the
rear
panel
barrier
strip.
If
the
XLR/QG
connectors
are
to
be
used,
install
the
accessory
Model
301
according
to
the
instructions
suppplied
with
the
adapter.
(See
also
"Mounting
Instructions,"
page
6A.)
If
the
Model
535
output
is
connected
to
a
high
impedance
circuit,
we
recommend
shunting
the"±"
and
"COM"
output
terminals
with
a
620
ohm,
1/2
watt
resistor.
This
assures
optimum
loading
for
the
535.
(See
section
2.6
regarding
input
termination).
(See
Figures
2
and
3
on
the
following
page)
-5-

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OUTPUT
GRD
INPUT
±
COM
COM
±
FIGURE
2.
CONNECTING
THE
MODEL
535
WITH
BALANCED
INPUT
AND
BALANCED
OUTPUT
CIRCUITS.*
OUTPUT
GRD
INPUT
±
COM
COM
±
FIGURE
3.
CONNECTING
THE
MODEL
535
WITH
UNBALANCED
INPUT
AND
UNBALANCED
OUTPUT
CIRCUITS.*
*With
a
balanced
input
and
unbalanced
output,
or
vice-versa,
use
the
appropriate
connections
suggested
by
each
of
the
above
diagrams.
No
special
switching
or
transformers
are
needed.
-6-

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2. 5. l
MODEL
301
XLR/QG
ADAPTER
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2.6
IMPEDANCE
AND
TERMINATION
Audio
engineering
had
its
roots
in
the
telephone
industry,
and
"600
ohm
circuits"
(together
with
their
predecessors,
"500
ohm
circuits")
are
carry-overs
from
telephone
transmission
practices.
Long
audio
transmission
lines,
like
their
video
counterparts,
must
be
properly
sourced
from
and
terminated
in
equipment
which
matches
their
characteristic
impedance,
if
optimum
frequency
response
and
noise
rejection
are
to
be
achieved.
However,
transmission
line
theory
and
techniques
are
not
only
unnecessary
but
impractical
within
modern
recording
studios,
broadcast
studios
and
other
local
audio
systems
where
transmission
circuits
are
seldom
more
than
several
hundred
feet
in
length.
The
advent
of
negative
feedback
circuitry
and
solid-state
electronics
has
spawned
modern
audio
amplifiers
and
other
signal
processing
devices
having
source
impedances
of
only
a
few
ohms.
They
are
essentially
indifferent
to
load
impedances
and
by
varying
their
output
current
inversely
to
changes
in
load
impedance,
maintain
the
same
output
voltage
into
any
load
impedance
above
a
rated
minimum,
with
no
change
in
frequency
response.
Modern
audio
systems,
therefore,
utilize
amplifiers
and
other
active
devices
which
have
very
low
output
impedances
and
high
(10k
to
50k)
input
impedances.
These
products
may
thus
be
cascaded
(operated
in
series),
or
many
inputs
may
be
connected
to
a
single
output
of
a
preceding
device,
without
regard
to
impedance
"matching''.
Switching,
patching,
etc.
is
simplified
because
''double
loads"
and
"unterminated"
bugaboos
are
essentially
eliminated.
"Floating''
(ungrounded)
transformer
outputs
minimize
ground
loop
problems,
and
differential
transformerless
input
circuitry
(or
input
transformers)
minimize
common
mode
noise
or
interference
which
may
be
induced
·
into
the
interconnecting
wires
or
cables.
Where
audio
must
be
transmitted
through
cables
or
wire
pairs
of
more
than
several
hundred
feet
in
length,
however,
transmission
line
termination
practices
should
still
be
observed.
The
Model
535
has
input
impedances
of
40
kohms
(40,000
ohms)
when
used
in
a
balanced,
differential
input
configuration,
and
20
kohms
(20,000
ohms)
when
used
unbalanced
(one
side
grounded).
This
makes
the
535
suitable
for
use
with
any
nominal
source
impedance,
low
or
high.
Only
when
it
is
used
from
a
source
which
requires
a
low
impedance
termination
(such
as
a
600-ohm
transmission
line
or
older
vacuum-tube
equipment)
will
a
source
termination
resistor
be
required
at
the
535
input.
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2.7 SIGNAL LEVEL AND OVERLOAD DETECTOR
The Model 535's differential input amplifiers are capable of
being driven by signals up to a level of +20 dB (Ref. 0.775 V rms),
above which clipping and distortion occurs. The overload LED turns
on when peak signals approach the clipping level, and it will remain
on long enough to be seen even if the excess signal is only a brief
transient. To avoid audible distortion, when the LED indicator
flashes more than occasionally, either lower the output level of
the source feeding the equalizer, or use an external attenuation
pad.
Because of the possible combination of control settings, the
overload is monitored at several points in the circuit:
1. Input amplifier (maximum signal level +20 dB,
ref. 0.775 V rms).
2. Filter amplifiers, which could be driven into clipping as
a result of boost equalization.
3. Output amplifier, which is capable of delivering +24 d~ n
into a 600-ohm load (12.3 V rms), or +26 dBm* into a
150-ohm load (7.75 V rms).
*NOTE: +26 dBm into 150 ohms is equivalent to +20 dB
referenced to 0.775 volts, i.e., 7.75 V rms.
2.8 ACCESSORIES
A
security cover (SC-1) may be installed over the front panel
of the Model 535 only. This protects all controls from unwanted
adjustments. Only the power switch remains accessible. The smoke
gray plexiglas cover is transparent enough to allow viewing of the
control settings. The Model 301 adapter is available for the use
of XLR/QG connectors; two are needed for the Model 535.
2.9 RACK MOUNTING A MODEL 533
The SR-21 kit (optional) allows mounting of one 533 in a
standard 19" USASI rack. The unit occupies two standard spaces
(3-1/2" high). The SR-21 kit should contain the following items:
QUANTITY
2
2
4
4
4
4
4
DESCRIPTION
Rack Adapter Angles
Rack Extensions
#6-32 Oval Head Screws
#6 Lock Washers
#6-32 Nuts
#8-32 Pan Head Screws
#8 Lock Washers
-8-
UREI PART NUMBER
25-12108
25-12109

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The
SR-21
Installation
Procedure
is
as
follows:
(Refer
to
Figure
4)
1.
Using
the
#6-32
screws,
lockwashers,
and
nuts,
mount
the
angles
to
the
back
side
of
the
rack
extensions.
Do
not
tighten
the
screws
at
this
time.
2.
Using
the
#8-32
screws
and
lock
washers,
mount
the
angle
and
rack
extension
assemblies
to
the
tapped
holes
in
the
sides
of
the
533.
Do
not
tighten
the
screws
at
this
time.
3.
The
533
front
panel
is
adjustable
to
allow
optimum
alignment
of
the
front
panel
with
the
rack
extensions.
For
precise
alignment,
loosen
the
front
panel
mounting
screws,
as
well
as
the
top
and
bottom
cover
screws
(1/2
turn
is
adequate).
Adjust
the
relative
positions
of
the
brackets
and
panels,
and
then
tighten
all
hardware.
SEE SECTION
2.5
BEFORE
INSTALLING
THE
ASSEMBLY
IN
A
RACK.
2.10
RACK
MOUNTING
TWO
UNITS
(MODEL
533)
The
DR-21
kit
(optional)
allows
mounting
of
two
533's
side
by
side
in
a
standard
19"
USASI
rack.
The
assembly
occupies
two
standard
spaces
(3-1/2"
high).
The
DR-21
kit
should
contain
the
following
items:
QUANTITY
2
2
2
4
4
DESCRIPTION
Joining
Plates
Rack
Mounting
Angles
Spacer
Plates
#8-32
Pan
Head
Screws
#8
Lock
Washers
The
DR-21
Installation
Procedure
is
as
follows:
(Refer
to
Figure
5)
URE!
PART
NUMBER
25-11168
25-12106
25-12107
1.
Place
the
two
533's
side
by
side,
with
front
panels
touching.
Remove
four
screws
from
the
top
of
each
unit~
as
illustrated,
to
permit
positioning
of
the
joining
plate.
Replace
the
screws
through
the
plate
and
covers,
but
do
not
tighten
completely
at
this
time.
2.
Turn
the
assembly
upside
down,
and
install
the
bottom
joining
plate
in
the
same
fashion
as
the
top
joining
plate
(step
1).
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3.
Using
the
#8-32
screws
and
lock
washers,
mount
one
angle
and
one
spacer
plate
to
each
side
of
the
533
assembly.
The
spacer
plates
should
be
located
between
the
angles
and
the
533
chassis.
The
mounting
holes
in
the
533
are
tapped,
so
nuts
are
not
required.
Do
not
tighten
the
screws
at
this
time.
4.
The
533
front
panels
are
adjustable
to
allow
optimum
alignment
of
the
front
panels
with
the
rack
mounting
angles.
For
precise
alignment,
loosen
the
front
panel
mounting
screws,
as
well
as
the
top
and
bottom
cover
screws
(1/2
turn
is
adequate).
Adjust
the
relative
positions
of
the
angles
and
panels,
and
then
tighten
all
hardware.
SEE SECTION
2.5
BEFORE INSTALLING
THE
ASSEMBLY
IN
A
RACK.
18-32
Pan
Head
Screw
18
Lock
Washer
16-32
Nut
16
Lock
Washer
#6-32
Oval
Head
Screw
screws
Rack
Extension
front
panel
mounting
screws
FIGURE
4.
MOUNTING
DETAILS
FOR
SR-21
RACK
MOUNT
KIT.
cover
screws
18-32
Screw
18
Lock
Washer
€,)
11
$0
II
II
II
11
~:6)
II
II
$110
Joining
Plate
Spacer
Plate
Angle
FIGURE
5.
MOUNTING
DETAILS
FOR
DR-21
RACK
MOUNT
KIT.
-10-

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SECTION
III
OPERATING INSTRUCTIONS
3.1
GENERAL
After
the
Model
535
Graphic
Equalizer
has
been
installed
and
is
connected
to
both
the
signal
source
and
the
succeeding
equipment
according
to
Section
II,
power
may
be
switched
ON.
Set
controls:
Gain
Control
All
Frequency
Controls
3.2
SYSTEM
CHECK
To
unity
gain.
To
the
zero
line
of
the
front
panel,
producing
no
effect
on
the
frequency
response.
Apply
program
material
and
monitor
the
output
signal
while
the
EQ
switch
is
in
the
OUT
position.
The
signal
should
be
passed
through
the
Model
535
without
loss
or
gain
in
amplitude,
or
frequency
alteration.
No
change
should
be
noticeable
when
the
EQ
switch
is
set
to
the
IN
position.
3.3
EXPERIMENTATION
To
become
familiar
with
the
range
and
effect
of
the
individual
filters
and
their
almost
unlimited
number
of
combinations,
it
is
helpful
to
"play"
with
the
controls
and
listen
to
the
change
in
-
some
familiar
program
material.
The
EQ
switch
is
very
useful
to
make
an
instant
A-B
comparison
while
altering
adjustments.
3.4
DOCUMENTATION
The
very
nature
of
a
graphic
equalizer
will
result
in
many
different
control
settings.
For
later
duplication
of
a
certain
sound,
or
of
a
corrective
filter
shape,
it
is
necessary
to
document
the
position
of
the
controls
(frequency,
boost
and/or
cut,
and
gain).
This
is
made
convenient
by
the
graphic
layout
of
the
Model
535's
front
panel
and
its
calibrated
markings.
In
addition,
a
frequency
curve
may
be
drawn
with
a
suitable
sweep
generator
and
X-Y
recorder
system,
such
as
the
UREI
Model
200/2000.
3.5
APPLICATION
It
will
be
helpful
to
study
the
editorial
in
the
following
paragraphs.
Although
the
section
is
not
intended
to
be
a
complete
textbook,
it
shares
some
of
the
experiences
we
have
gained
during
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the
years
our
equalizers
have
been
in
use.
Also,
it
should
serve
as
a
stimulant
to
experiment
with
the
instrument.
We
believe
that
it
is
of
primary
importance
for
the
user
to
know
and
understand
the
equipment
and
its
capabilities.
Some
sections
may
not
be
of
interest
at
this
time,
however
it
is
beneficial
to
read
through
the
entire
text.
As
in
any
other
field,
"practice
is
the
key
to
success."
Just
as
it
is
not
reasonable
to
expect
to
get
beautiful
music
out
of
a
musical
instrument
the
first
time
you
play
on
it,
it
is
also
not
reasonable
to
expect
to
immediately
master
the
techniques
necessary
to
adjust
the
Model
535
for
the
desired
sound
the
first
time
you
work
with
it.
Some
of
its
many
uses
are
listed
below:
(1)
Recording
studio
frequency
shaping
of
recorded
material.
The
very
low
output
noise
and
high
signal
handling
capability
make
the
Model
535
suitable
for
use
in
any
studio
situation.
(2)
Reduction
of
proximity
effect
due
to
close-talking
use
of
cardioid
microphones.
A
decrease
of
only
2 dB
or
so
in
the
200
to
400
Hz
region
may
significantly
improve
the
intelligi-
bility
of
what
otherwise
would
be
a
very
"boomy"
sound.
(3)
Elimination
of
excess
high
frequencies
and
sibilance,
especially
at
high
sound
pressure
levels.
A
slight
reduction
in
level
at
8 kHz
may
eliminate
much
of
the
harshness
which
is
experienced
when
loudspeakers
and
amplifiers
are
operated
close
to
their
power
limits.
(4)
Sound
effect
processing
such
as
"Telephone
Sound."
(5)
Room
equalization.
(6)
Sound
effects
tapes
for
theatrical
productions
may
be
made
through
the
Model
535
to
ensure
consistency
of
quality
of
the
recorded
material,
and
to
pre-equalize
for
correct
sound
from
the
particular
loudspeakers
to
be
used.
If
the
tapes
are
correctly
equalized,
adjustments
during
the
show
are
reduced
to
volume
adjustments
and
speaker
selection.
If
the
show
goes
on
the
road
to
some
other
auditorium,
the
Model
535
may
be
inserted
in
the
line
to
account
-
for
different
acoustics
while
retaining
the
original
total
balance
of
sounds
from
effect
to
effect.
(7)
Many
sound
systems
are
required
to
serve
rooms
in
which
dif-
ferent
acoustic
environments
prevail
in
different
areas:
for
example,
the
under
balcony
area
of
a
theatre
versus
the
balcony
area.
For
such
installations,
use
of
one
half
of
a
Model
535
for
one
area
and
the
other
half
of
a
Model
535
for
another
area
may
allow
for
more
consistent
response
throughout
the
room.
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3.5.1.
OBJECTIVE
MEASUREMENTS
vs.
SUBJECTIVE
HEARING
Since
the
hearing
process
is
subjective,
each
individual
will
have
a
different
opinion
of
what
constitutes
"good
sound"
or
"bad
sound".
Until
science
has
found
all
the
answers
about
the
phenomenon
of
hearing,
we
will
have
to
use
the
available
tools
to
modify
sound
with
a
certain
imprecision.
This
lack
of
ability
to
quantify
the
relationship
which
exists
between
the
subjective
response
of
the
listener,
and
the
objective
measurements
of
amplitude-vs-frequency
response,
phase,
distortion,
etc.,
need
not
be
a
barrier
to
our
efforts
to
"improve"
the
sounds
that
we
hear.
We
have
a
most
sophisticated
quality
assessment
mechanism
which
is
specifically
suited
to
do
this
job
..•
the
human
ear.
Therefore,
the
educated
listener
with
good
hearing
will
probably
always
be
the
standard
of
reference
to
decide
if
a
sound
has
been
accurately
reproduced.
However,
accurate
faithful
reproduction
is
not
always
the
goal,
and
in
many
circumstances
it
may
not
even
be
possible
or
desirable.
3.5.2.
ADDITIONAL HINTS
The
Model
535
Graphic
Equalizer
is
a
powerful
tool
for
the
audio
engineer
to
modify,
adjust,
alter,
enhance,
destroy
or
reclaim
the
audio
signal.
The
extreme
result
would
be
a
sound
that
never
existed
before.
In
such
instances,
there
are
very
few
rules
for
what
to
do
and
what
not
to
do
with
the
equalizer
controls
..•
in
creative
equalization:
whatever
works
is
right.
It
is
good
to
begin
the
work
in
a
controlled
environment
where
there
is
enough
time
to
experiment,
and
the
freedom
to
do
it
''wrong"
without
offending
someone
else.
Doing
it
the
wrong
way
means
to
know
what
does
not
work!
Start
out
with
simple
program
material
of
various
types
and
try
to
make
it
sound
"better."
Different
program
material
will
require
different
control
settings.
Extreme
filter
settings
are
generally
to
be
avoided.
Of
course
special
effects
and
corrective
equalization
of
program
material
which
must
be
saved
may
require
such
settings.
The
important
thing
is
to
avoid
creating
a new
problem
while
correcting
another.
Whenever
a
big
notch
in
the
frequency
response
of
the
filter
is
selected,
it
can
cause
important
parts
of
the
program
material
to
be
removed.
It
is
possible
to
make
adjacent
notes
on
the
musical
scale
differ
considerably
in
level.
If
that's
what
is
desired,
fine.
However,
if
you
are
trying
to
correct
for
problems
which
would
better
be
dealt
with
by
choice
of
microphone,
microphone
positioning,
acoustic
control,
etc.,
you
may
run
into
trouble.
The
535
(or
any
other
such
device)
is
not
a
lifesaver
in
an
ocean
of
problems.
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3.5.3.
SPECTRAL DISTRIBUTION IN
THE
AUDIO
SIGNAL
It
may
seem
obvious,
but
we'll
point
it
out
anyway;
a
major
advantage
of
a
graphic
equalizer
is
to
be
able
to
see
at
·a
glance
what
the
instrument
is
doing.
The
shape
of
the
filter
response
is
apparent
immediately
from
the
positions
of
the
slide
controls.
This
information,
together
with
the
knowledge
of
the
spectral
distribution
of
the
program
material,
is
very
advantageous
in
arriving
at
a
desired
frequency
response.
We
can
arbitrarily
divide
the
audible
frequency
spectrum
into
four
sections:
bass,
lower
midrange,
upper
midrange,
and
high
frequencies.
When we
are
concerned
with
wide
bandwidth
program
material,
we
should
remember
that
each
of
these
frequency
bands
is
important
for
its
contribution
to
a
full
and
balanced
sound.
Lack
of
bass
frequencies
will
make
the
sound
thin,
while
too
much
will
make
it
boom.
The
lower
midrange,
which
provides
much
of
the
rich
and
mellow
texture
to
music,
may
make
the
program
material
sound
muffled
if
too
abundant.
The
upper
midrange
is
necessary
for
clarity
and
articulation,
but
gives
the
program
a
"canned''
quality
if
overused.
The
high
frequencies
in
excess
create
a
harsh
sound,
but
if
balanced,
give
the
audio
program
a
spaciousness
which
it
would
not
otherwise
have.
3.5.4.
EQ
SYSTEMS
AND
LIMITERS
The
use
of
a
compressor
or
limiter
in
the
audio
chain
is
frequently
dictated
by
the
system's
headroom
restraint,
the
dynamic
range
of
program
material,
or
aesthetic
reasons.
The
question
then
arises,
"do
I
put
the
limiter
before
or
after
the
equalizer?"
The
answer
is
that
generally
the
equalizer
should
be
ahead
of
the
limiter
in
the
chain.
The
equalizer,
by
its
very
nature,
changes
the
frequency
balance
and
harmonic
relationships
of
the
input
signal.
Frequencies
that
were
greatest
in
amplitude
at
the
input
may
not
be
so
at
the
output.
Conversely,
some
frequencies
may
be
at
a
high
level
at
the
output
due
to
the
equalizer's
action.
The
limiter,
which
is
actuated
by
the
level
of
the
signal,
should
see
the
equalized
or
balanced
signal.
The
use
of
the
equalizer
prior
to
the
limiter
offers
a
further
advantage,
i.e.,
the
program
material
may
be
equalized
to
optimize
the
limiter
output
by
adjusting
the
input
signal
to
the
limiter.
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As
an
example,
if
a
recording
has
a
large
dynamic
range
and
an
excess
of
low
frequencies,
the
equalizer
would
be
able
to
reduce
the
level
of
the
low
frequencies
fed
to
the
limiter,
thereby
reducing
the
amount
of
limiting
needed.
It
also
enables
the
user
to
select
a
faster
attack
and
release
time
on
the
limiter
if
needed
for
peak
limiting.
The
excessive
low
frequencies
would
have
restricted
the
speed
at
which
the
limiter
could
operate
and
still
achieve
the
desired
low
distortion.
There
are
a
few
instances
where
the
equalizer
might
be
placed
after
the
limiter,
and
that
would
be
in
a
system
where
extreme
uncontrollable
dynamics
are
expected.
These
might
otherwise
overload
the
Model
535.
However,
these
cases
are
very
rare,
and
the
exceptionally
wide
dynamic
range
of
the
535
makes
this
situation
even
more
unlikely.
3.6
DISCUSSION
OF
EQUALIZATION
The
main
reason
for
frequency
response
tailoring
of
audio
systems
is
to
compensate
for
response
anomalies
occurring
in
the
system
and
its
environment,
and
to
adjust
the
system
response
curve
to
some
desired
shape.
In
some
systems
this
means
adjusting
for
best
overall
flatness
of
response
through
the
entire
audio
range,
and
in
other
instances
some
different
response
shape
is
desirable.
Three
important
characteristics
of
audio
systems
may
be
improved
by
judicious
application
of
corrective
equalization
techniques.
They
are:
(1 )
( 2 )
DISTORTION
OF
FREQUENCY
RESPONSE
BALANCE.
_
Sources
of
sound
which
may
be
amplified
through
a
sound
system
start
out
with
some
specific
frequency
balance.
If,
in
being
processed
through
an
audio
system
this
balance
is
disturbed
by
variation
in
frequency
response,
then
truly
the
sound
has
been
distorted.
For
example,
an
instrument
has
a
specific
characteristic
with
regard
to
the
levels
of
the
various
harmonics
compared
to
the
fundamental
tone.
If
these
signals
are
processed
through
an
audio
system
with
non-linear
frequency
response,
then
the
resultant
sound
is
simply
not
the
distinctive
sound
which
that
instrument
orignally
produced.
SUSCEPTIBILITY
TO
FEEDBACK.
In
public
address
and
sound
reinforcement
systems,
the
maximum
acoustic
gain
that
may
be
obtained
for
a
micro-
phone
in
the
vicinity
of
a
loudspeaker
which
is
part
of
that
system,
will
be
determined
by
the
positive
feedback
loop
created
when
sound
from
the
loudspeaker
en
·
ters
the
microphone,
reinforcing
the
signal
level
until
the
system
goes
into
oscillation.
This
positive
feedback
problem
is
aggravated
if
some
frequencies
in
the
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