Dorrough 40-A, 40-B, 10-A, 10-B, 12-A Instruction Manual

Technical Instruction Manual

DORROUGH

LOUDNESS MONITOR

Model 40-A

- 4

- 6

- 8

-10

-12

-14

-16

-18

-20

-22

-25

dB

NORMAL

PERSIS

TENCE

RANGE

- 2

0

+ 2

+ 4

+ 6

+ 8

+10

+12

NORMAL

PEAK

RANGE

+14

dB

LOUDNESS MONITOR

DORROUGH

RELATIVE LOUDNESS

TO PEAK MODULATION

Model 40-B

10

LATION

-30

5

4

-26

-28

% MODU

3.2

2.5

2

1.6

-32

-34

-36

dB

RELATIVE LOUDNESS TO PEAK MODULATION

6.3

-24

-22

8

-20

-18

MODEL 40-A

-10

% MODU

32

- 8

LATION

40

50

63

80

100

125

- 6

- 4

- 2

0

+1

+2

+3

dB

MODEL 40-B

16

12

-16

-14

20

25

-12

Also covers Models 10-A(B), 12-A(B), 20-A(B), and 21-A(B)

DORROUGH ELECTRONICS

5221 Collier Place

Woodland Hills, CA 91364

[phone]

INTRODUCTION

Today’s audio requires careful attention to precise level control. The con­sumer now has audio playback systems that stretch the limits of program
dynamics. With all this new equipment, the modern listener is able to hear
subtle differences in level and distortion within program material and make
critical program choices based on the quality of sound.

Now it is more critical for the engineer to obtain the maximum loudness with
the minimum of distortion components in order to fully utilize the dynamic
range available. With the dynamic range that digital audio offers, and the
bandwidth now available to film and video productions, it has become of
paramount importance that there be a new method of monitoring and
establishing the maximum safe level at which a system can operate.

The Weston (VU) Meter

The American Standard...

80

100

60

40

-2

-1

-3

20

0

-20

VU

-5

+1

-7

-10

+2

+3

The European Standard...

4

3

2

1

5

6

7

The Weston meter, introduced in 1939, was the standard for level monitoring.
It met the then new standard for VU (Volume Unit) meters, and those same
specifications are still the standard for all VU meters in use today. VU
meters are really nothing more than voltmeters calibrated in power, and
their ballistics were chosen to represent program material of the early days of
radio and film.

A VU meter is classified as a quasi-average reading device. It almost com­pletely ignores peak waveforms. With the somewhat arbitrarily chosen rise
time of 300 µs, engineers have developed certain compensations, such as
riding dialogue 3 to 5 dB below music, to control the peak levels in an
attempt to attain consistent listening levels. The standard broadcast practice
is to allow for a crest factor of at least 10 dB to cover the peak excursions of
the waveform that the VU meter is too slow to indicate.

The VU meter was never intended to provide acoustical comparisons be­tween processed and unprocessed program material. Nor was it ever
intended to provide indications of peak excursions. Clearly, the VU meter
has some dramatic shortcomings with today’s dynamic program material .

The PPM Meter

The PPM (Program Peak Meter) meter is not quite as old as the VU meter,
being only about a forty-year-old standard, but like the old VU meter, the
original standards are still on the books today. The PPM meter was the first
answer to the obvious shortcomings of the VU meter, but, because it displays
and holds only the peak level of the waveforms, the integration time of
quasi-average program level is almost completely ignored.

The PPM also has a scale that does not relate directly to measured program
levels, but only indicates relative levels. The numbers are arbitrary and
could be just as well represented by fruit symbols or stick figures. Modern
technology has eliminated the need to stare at a narrow mechanical needle
oscillating in an analog motion to set level.

1

Peak hold circuits have been suggested as a solution, but while holding a
peak reading, they ignore any information that occurs during the decay time.
An engineer must make an adjustment, then wait while the peak hold circuit
decays to get an indication of the new setting. Obviously this method cannot
be used because of the need to respond to program material in real time.

Most contemporary studios have tried to solve their metering problems by
using both VU and PPM meters on the same source in an attempt to get the
maximum usable level out of a piece of program material. This has led to
cramped and overly complex metering bridges and panels, and does not
overcome the limitations inherent in these systems. Even the switchable bar
graph meters offered as a solution by some console manufacturers suffer
from the same ballistic limitations.

Loudness Meter

A new standard...

8

LATION

6.3

5

% MODU

4

3.2

2.5

2

1.6

-34

-36

dB

RELATIVE LOUDNESS TO PEAK MODULATION

-22

-24

-26

-28

-30

-32

Years of hands-on experience and frustration with both VU and PPM meter­ing led to the development of the DORROUGH Loudness Monitors.

10

-16

-18

-20

LATION

32

40

50

63

80

100

-14

-12

-10

125

- 8

- 6

- 4

- 2

0

+1

+2

+3

MODEL 40-B

% MODU

16

12

20

25

DORROUGH’s research has established the relationship between integration
time, RMS metering and the display of peak levels.

dB

The DORROUGH Loudness Monitor displays, in an easy-to-read format, the
actual energy content of the program material, regardless of frequency, while
still indicating the peak amplitude of the complex audio signal. It allows the
operator to ride levels in a manner such that all program material can be
adjusted for equal perceived loudness while protecting the peak of the
waveform. Now, one meter gives you more complete and more usable
information than any combination of peak hold, VU and PPM indicators.

The DORROUGH Loudness Monitor integrates on the same scale, two
ballistics, showing the relationship between the average and the peak. It
simultaneously displays peak and average, and the relative difference, in dB,
between these two ballistics is derived from the integration time of the
persistence scale.

The operator has only to adjust the level until either the peak or persistence
reference is reached. This will result in the maximum level, regardless of
program content. Material with or without compression can easily be
matched for the same listening level.

Each DORROUGH Loudness Monitor features Right and Left inputs for use
in stereo mixing applications. With one instrument, the operator can easily
see the stereo mix and avoid the classic in-phase/out-of-phase problem.
“Center channel build-up,” the addition of in-phase or monophonic material
which causes the mix to be perceived as louder, will appear as a sudden
increase in level. This is especially important in preparing stereo program
material for broadcast, while still being able to maintain monaural compati­bility.

2

INSTALLATION

To install your DORROUGH Loudness Monitor, perform the procedures
described in the following sections.

Unpacking

Your DORROUGH Loudness Monitor was carefully packed at the factory.
Take a moment to examine the unit for any signs of shipping damage. If
damage is evident, retain the carton and notify the transit carrier and your
local distributor about your claim.

Once you are satisfied with the physical integrity of the unit, proceed with
Initial Set-Up to align the meter to match your operating level requirements.

Initial Set-up

You can set the operating level either on the bench or at the installation
location. For set-up at the installation site, refer to the section on Mounting
Considerations prior to performing the following procedure.

1. Plug the AC cord into a convenient AC line and observe that the display
becomes backlit.

☛

☛

NOTE: If you do not see this action, make sure the AC line has power and the
Power Switch (recessed in the back panel) is in the ON (up) poasition, or test the
internal 0.25 A fuse for continuity.

2. While observing polarity, feed a 1000 Hz sine-wave at a standard operat­ing level (i.e., -10, +4, +8, etc.) into the left input, as shown in Fig. 1.

3. Adjust the input level control (Fig. 1) on the rear panel for an indication
of “0” on the meter scale. This step applies to all models.

NOTE: The peak excursion and the persistence amplitude are equal under
steady state sine-wave conditions.

4. Next, remove the signal from the left channel and feed the signal in the
same polarity to the right input, making the same adjustment.

5. Following the adjustments for both the left and right inputs, feed the
signal to both inputs simultaneously. The summing amplifier will
algebraically add the two inputs for an indication of +6, as read on the
PEAK scale. This action applies only to an "A" Type meter; a "B" Type
meter would be "off scale" for the same summing condition.

Continued on Page 4...

3

...Continued from Page 3

In actual practice, a "B" Type meter is generally used as a discrete
monitor to indicate either a left or right channel. However, for Sum and
Difference monitoring, repeat steps 3 and 4 (previous page), and adjust
each input level control for a -6 dB indication on the meter scale for an
individual channel. This action will result in a proper sum of "0" on the
"B" Type meter scale.

☛

ON

NOTE: Different amplitudes and phase angles between the left and right input
signals will produce different algebraic sums. This display is essential in
indicating center channel buildup in some program material and will aid an
operator in making the proper adjustment to program operating level. For mono
signals, use the suggested connections shown in Fig. 2.

PAT. PEND.

+- - +
LIN RIN

Meter Connections

DORROUGH ELECTRONICS USA
WOODLAND HILLS, CA 91364

LR

Recessed
Power Switch

AC Cord

Input Gain Controls
VR13 (L) and VR14 (R)

Fig. 1. Back panel of DORROUGH Loudness Monitor, Model 40-A or
Model 40-B.

Fig. 2. Meter connections for mono and stereo input signals.
For mono use, connect mono input signal to L+ and L- terminals
and turn R Input Gain Control to the full counterclockwise
position.

4

+­Mono

Input

+- - +

Stereo L
Input

Stereo R
Input

Mounting Considerations

The DORROUGH Loudness Monitor is available with or without a case, and
is manufactured in several versions to accommodate differing customer
needs. For example, "A" Type models are the standard Loudness Monitors,
while "B" Type models measure Relative Loudness to Peak Modulation (see
front cover).

Fig. 3 and Fig. 4 show the physical specifications for mounting one or two
meters with their cases in a rack panel. Fig. 5 shows the physical mounting
specifications for each panel mount model (no case), while Fig. 6 illustrates
the procedure for installing a panel mount meter.

19.00 "

3.50 "

- 4

- 6

- 2

- 8

-20

-22

-25

dB

NORMAL

LOUDNESS MONITOR

-10

-12

-14

-16

-18

RANGE

TENCE

PERSIS

0

+ 2

+ 4

+ 6

+ 8

+10

+12

NORMAL

+14

PEAK

dB

RANGE

MODEL 40-A

PANEL #40A-S

3.00 "

-20

-22

-25

dB

NORMAL

LOUDNESS MONITOR

8.125 "

Fig. 3. Physical specifications for mounting a single meter in a rack panel.
As an installation aid, an optional rack panel (40A-S) is available from the
factory. Meter slides in from the back and is fastened to the tray with two
4-40 x 3/4" screws.

PANEL #40A-D

- 4

- 6

- 2

- 8

-10

-12

-14

-16

-18

RANGE

TENCE

PERSIS

0

+ 2

NORMAL

+ 4

+ 6

+ 8

+10

+12

+14

PEAK

dB

RANGE

MODEL 40-A

-25

dB

LOUDNESS MONITOR

-14

-16

-18

-20

-22

TENCE

PERSIS

NORMAL

- 4

- 6

- 2

- 8

-10

-12

RANGE

0

+ 2

+ 4

+ 6

+ 8

+10

+12

NORMAL

+14

PEAK

dB

RANGE

MODEL 40-A

6.50 "

16.250 "

Fig. 4. Physical specifications for mounting two meters in a standard rack
panel. As an installation aid, an optional rack panel (40A-D) is available from
the factory. Meter slides in from the back and is fastened to the tray with
four 4-40 x 3/4" screws.

5