Dorrough 380 Technical Instruction Manual
Digital Loudness Meters
Model 280 and 380
Technical Instruction Manual
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U.S.A. 380-D
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MODEL 280-E U.S.A.
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MODEL 280-D U.S.A.
Model 280-D
Model 280-E
Digital Loudness Meters
Model 280 and 380
April, 1999
Copyrigh t © 1994 and 1999 by Dorroug h Electronics, 20434
Corisco S t., Chats wort h Ca li fo rni a, 91 311.
PH 818. 998.2824, FAX 818. 998.1507.
Dorrough Electronics reserves the right to make changes and
improvements in product specifications without notice.
Introduction 1
Introduction 1
1.1. Loudness Monitoring
Double Standards
For nearly 60 years the world has used two different standards for audio
monitoring. In the United States, the VU meter, introduced in 1937, was the
standard for level monitoring. In Europe, the PPM (Program Peak Meter)
was the standard.
The VU meter is a quasi-average reading device. Basically a voltmeter
calibrated in power with ballistics chosen to represent early radio and film
program material, it was never intended to indicate the peak excursions
found in today’s program material.
The PPM addressed the limitations of the VU meter, but because it displays
and holds only the peak level of the waveform, the integration time of the
quasi-average program level is almost completely ignored.
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 of these systems. Even the switchable bar graph
meters offered as a solution by some console manufacturers suffer from the
same ballistic limitations.
Unification
In 1980, after years of hands-on experience and frustration with both
conventional VU and PPM metering, Dorrough research led to the
introduction of the Dorrough Model 40 Loudness Meter. By providing an
easy to understand display showing the relationship between integration of
RMS and peak level display, the model 40 was an overnight success. Today
the model 40 is regarded as the standard in audio monitoring and is used
throughout recording and broadcast facilities around the world.
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2 Introduction
The Dorrough Loudness Meter gives you a much more accurate picture of
the actual energy content of audio program material than conventional
metering. By simultaneously displaying two ballistics, the Dorrough
Loudness Meter shows you the relationship between average and peak.
You need only adjust the program 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.
1.2. Digital Audio an d the Do r rou gh Loudne ss Meter
Into the Digital Domain
The Audio Engineering Society (AES), together with the European
Broadcasting Union (EBU), have established a digital audio interface
standard known as the AES/EBU interface. This standard provides robust
formats for the exchange of digital audio information between professional
audio devices, yet also provides flexibility for specialized applications. The
International Electrotechnical Commission (IEC) has also endorsed a
format based on the AES/EBU standard for consumer digital audio devices.
Briefly, the AES/EBU format standard defines how two channels of audio
information are periodically sampled, uniformly quantized and transmitted
over a twisted wire pair. Left and Right audio channels are multiplexed, and
the channel is self-clocking and self-synchronizing. The format is
independent of sampling frequency and can be used with any sampling
frequency including 32 kHz, 44.1 kHz, and 48 kHz, which are those
recommended by AES for PCM applications.
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LOUDNESS MONITOR MODEL 40-A
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Introduction 3
New Challenges
The wider dynamic range provided by this standard also poses new
challenges in monitoring. The trend to obtain a “hotter” signal typically
involves more sophisticated processing and compression. The narrowing
gap between average level and peak level means more accurate monitoring
is necessary to obtain desired results.
Another important consideration in today’s digital recording and
broadcasting include monitoring the “crash point”, or the point of reaching
the maximum input level the system or equipment can handle.
The Dorrough Digital Level Meters have been designed to meet these needs
with unprecedented accuracy, flexibility and convenience in the Dorrough
tradition.
1.3. The Dorrough 280 and 380
The Dorrough model 280 and 380 Digital Loudness Monitors (DLMs)
provide the same basic functionality as the classic 40 series analog loudness
meter except that they accept a digital data signal and display two channels.
Horizontal or Vertical Mounting
The model 280 is designed for horizontal mounting while the model 380 is
designed for vertical mounting. Both models are offered with two scale
ranges, a standard 40 dB range (-D suffix), and an expanded 60 dB range
(-E suffix). Figure 1-1 illustrates the model 280 with both scale options,
while Figure 1-2 shows the model 380 with both scales.
Figure 1-1. 280 Front Vie
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-57 -54 -51 -48 -45 -42 -39 -36 -33 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0
MODEL 280-E U.S.A.
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MODEL 280-D U.S.A.
Model 280-D
Model 280-E
4 Introduction
Two Channel Display
As defined by the AES/EBU Digital Audio specification, two audio
channels (A and B) are encoded into the serial datastream. On the model
280, Channel A (corresponds to Left), is displayed on the top scale, while
Channel B (Right) is displayed on the lower scale. On the model 380,
Channel A is displayed on the left scale, and B on the right.
When multiple meters are installed in a console, channel designation can be
made on the meter bezel (if used), or the meter bridge front panel.
Figure 1-2. Model 380 Front Vie
40 dB or 60 dB Scale
Both the model 280 and 380 are available with either 40 dB or 60 dB scale
ranges. The “D” suffix (40 dB) uses 40 discrete LED indicators, each
representing one dB. This scale provides an absolutely linear cadence of the
display as a function of level, which is not obtainable with conventional VU
metering where the metering ballistics vary with signal level.
The 60 dB scale (“E” suffix) is available for applications requiring
observation of a wider range of signal levels. This scale also provides one
dB indications from 0 to -30dB, with the remaining nine LEDs indicating
three dB steps (-33 to -60 dB).
Either scale is available from the factory as an option.
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U.S.A. 380-D
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U.S.A. 380-E
380-D
(40 dB
scale)
380-E
(60 dB
scale)
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