Dorrough 280 Owner's 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

Corisco St., Chatsworth California, 91311.

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

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

RMSand peak level display, the model 40 was an overnightsuccess. Today

the model 40 is regarded as the standard in audio monitoring and is used

throughout recording and broadcast facilities around the world.

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 and the Dorrough Loudness 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. Leftand Rightaudio 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.

LOUDNESS MONITOR MODEL 40-A

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 leveland 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 functionalityas the classic 40 series analog loudness

meter except that they accept a digital data signaland 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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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 multiplemetersare 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 providesan absolutely linearcadence of the

display as a functionoflevel, whichis 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)

Introduction 5

Overrange Indication

Overrange indication occurs whentheinput signal reaches a point one count

over maximum allowed input level. When this happens, the top three LEDs

(0, -1, and -2) all change color to red while tracking the program level.

Overrange indication is set atthe factory to occur at the point one count over

the maximum signal level (the maximum level is the point at which the

signal becomes all binary 1’s). This point can alternately be set to 4 counts

over the maximum signal level by moving a jumper.

Peak Hold Functions

Both the model 280 and 380 provide three peak hold functions: 3-second

peak hold (normal), indefinite peak hold, and no peak hold. These functions

are selected through a three-position toggle switch (supplied), or if only a

single function is desired, jumper selected on the DLM main circuit board.

Normal operation (peak hold for 3-seconds) is provided at the center

position of the toggle switch, or through jumpering as described in Section

4 of this book. In this mode, the highest peak is held for 3-seconds before

being reset.

Indefinite peak hold retains the highest peak that has occurred for an

indefinite period while constantly resampling. This function is particularly

useful for unattended operation where the engineer wishes to record the

highest audio peak occurring during a mastering operation, or at a remote

transmitter site, etc. The peak is cleared by switching the toggle switch to

normal, then back to indefinite peak hold.

Peak hold operation may also be completely defeated. In this mode, peaks

are displayed in real time.

1.4. Specifications

Compatibilit

Conforms to all formats defined within the AES/EBU Digital Audio

specification, including IEC 958, S/PDIF, and EIAJ CP-340 interface

standards.These standards include professional 24-bit and consumer 16-bit

formats. Sampling frequencies include 32 kHz, 44.1 kHz, and 48 kHz.

Signal Interface

RS-422 levels over 75-ohm single-ended and 110-ohm balanced inputs.

Transformer isolated (as dictated by the EBU specification) with series DC

blocking capacitor on input and output. A buffered feed-through is also

provided. These signals are not polarized.

Scales

“D:” 40 dB in one-dB steps

“E:” 60 dB in one dB steps from 0 to -30 dB, and 3-dB steps from -33 to

-60 dB.

6 Introduction

Accuracy (both scales)

Worst case error: +1.4% to -0.8% of full scale. Typical: better than 0.35%

of full scale error.

Peak Hold Functions

Normal (3-Second Peak Hold), Indefinite Peak Hold, or no Peak Hold.

Overrange Indication

Top/rightmost 3 LEDs change color to red while tracking the programlevel

peaks when the overrange trigger point is reached. The trigger point is

jumper selectable between 1-count over (factory default), or 4-counts over

the maximum input level.

Electrical Connections

All signal, power, and peak hold functions are made to the unit through an

eight-pin Euroconnector. Electrical connections are made through screw

terminals in the connector.

Power Requirements

7 VDC at approximately 600 mA.

Dimensions

Bezel: 1.45” x 5.00”.

Mounting

Fits standard 1.45” console opening (minimum 5.0”height and 5.5” depth).

Bezel supplied.

Weight

Approximately 1 pound.

Options

– Rack mount adapter for one to three units (model 280 only).

– 40 dB or 60 dB scale overlay.

Accessories Supplied

– 120VAC or 220VAC power adapter

– Peak Hold Toggle Switch (3-position) with cable and plug

– Mounting bezel

– Technical Instruction Manual

Installation 7

Installation 2

2.1. General

Installation of the DLM is straightforward and easy. When multiple DLMs

are installed in a console the use of a common power supply is

recommended. Installation procedures are provided in the following

sections.

Your Dorrough model 280 or 380 Digital Loudness Meter is warranted for

a period of one year from date of purchase. Be sure to complete and return

the Warranty Registration Form to activate the warranty.

2.2. Unpacking

All Dorrough Digital Loudness Meters are carefully packed at the factory,

however, if any damage is evident, retain the packaging 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

the installation procedure.

2.3. Mounting

280

The model 280 is designed for horizontalmounting in a console or rack. For

console installation, the unit mounts in a standard 1.45” by 5.0” cutout. If

you intend to install the unit in a rack, a optional rack adapter are available

as shown in Figure 2-1. Contact the factory or your sales representative for

ordering information.

380

The model 380 is designed for vertical mounting in a console having

standard 1.45” by 5.0” cutouts. If plan to install the meter in a custom

console or equipments and do not wish to use the bezel supplied, cutout

dimensions can be taken from the inside opening of the bezel.

Contact the factory for alternate mounting options.

An illustration ofdetailed measurements useful for mounting the model 380

in a console is provided at the rear of this book.

8Installation

Figure 2-1. Model 280 Rack Mount Adapters

2.4. Electrical

There are three types of electrical connections to the DLM: digital signal

input (and optional output), peak hold function selection, and DC power.

Signal Connection

The DLM is designed to operate with either professional balanced input

lines using a shielded twisted pair, or unbalanced lines using coaxial cable.

Wiring foreach is shown in Figure 2-2. Signal connections should be made

to the corresponding terminal of the meter’s Euroconnector.

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MODEL 280-E U.S.A.

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MODEL 280-E U.S.A.

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MODEL 280-E U.S.A.

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MODEL 280-E U.S.A.

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