LM100 Broadcast Loudness Meter

Dolby Broadcast Loudness Meter LM100

The Dolby® Broadcast Loudness Meter LM100 is a tool for measuring the subjective loudness of dialogue within broadcast programming.

Differences in audio levels between programs, or between programs and commercials, are a major annoyance to TV viewers. However, although obvious to the viewer, these differences have proven difficult for broadcasters to measure with conventional methods and equipment. The Dolby Broadcast Loudness Meter LM100 solves that problem through Dialogue Intelligence™, a revolutionary technology developed specifically to measure the perceived loudness of dialogue.

Research shows that most viewers adjust TV volume to normalize dialogue levels. By analyzing the input signal and measuring program loudness only during the presence of speech, Dialogue Intelligence objectively measures what viewers subjectively experience.

Dolby LM100 Applications

Applications for the LM100 range from postproduction and quality control to final transmission, program turnaround, and cable head-end facilities.

Easy-to-Read Measurements on the LM100

The LM100 can use ITU-R BS.1770-1 and BS.1770-2 as the core measurement algorithm. Users can also select Leq(A) or EBU R128. For units manufactured prior to September 2011, Dolby offers a software upgrade option that adds the latest features, including the ITU-R BS.1770-2 algorithm.

The LM100 presents its measurements in an easy-to-understand numerical format. This eliminates the variations in results that multiple operators often find when using VU or PPM meters, neither of which was designed to measure subjective loudness. The LM100 can also determine the unweighted peak and a range of other information about the signal, including the Loudness Range measurement specified by the EBU. The unit can simultaneously display the incoming dialogue normalization (dialnorm) value of a Dolby Digital program (or any program within a Dolby E bitstream) for direct comparison to the actual measured value.

Front- and rear-panel serial interfaces provide capabilities for software updates and the LM100 software remote application. The remote application will assist users with advanced loudness measurement, logging features, and enhanced error reporting.

A set of user-definable alarms and monitoring functions can inform an operator of input loss, signal clipping, overmodulation (LM100-NTSC version), high or low signal levels, silence, and incorrectly set dialnorm values.

Dolby LM100 Configurations

The LM100-LTC includes a timecode input, which allows alarm and other signal conditions to be logged to either the internal time-of-day clock or external timecode. The LM100-NTSC includes an RF input specifically for NTSC CATV and “off-air” television measurement applications. Because the RF tuner replaces the linear timecode input in this version, logging is referenced to the internal clock.

LM100 Broadcast Loudness Meter Front View Medium
LM100 Broadcast Loudness Meter Rear View Medium
ENLARGE green arrow wht bkg

LM100 Front Panel

Display and Controls

Intuitive, easy-to-read user interface; input source selection determines display parameters


Enables local control of setup functions and status display

Alarm LEDs

Audio alarm, fault, and error

Headphone Output

6.35 mm (1/4-inch) standard stereo headphone jack, level-adjustable for confidence monitoring

RS-232 Serial Remote Control Input Port

8-pin female mini-DIN connector for the LM100 software remote application and software upgrades

LM100 Rear Panel

Digital Audio Input

BNC female connector with loop-through, unbalanced, 75Ω, signal levels per AES-3ID-1995 (SMPTE 276M), external 75Ω termination required
Formats supported: PCM data up to 24 bits; Dolby E data supported in 16-, 20-, and 24-bit modes at 48 kHz; Dolby Digital (AC-3) data at 32, 44.1, and 48 kHz sample rates

Analog Audio Inputs

Two Neutrik® combination XLR/¼-inch TRS connectors, electronically balanced; maximum input level: ~ +22 dBu
Input impedance: 10 kΩ; user-definable nominal operating levels

Analog Audio Outputs

Two RCA-type connectors, unbalanced, stereo; maximum output level: 2 Vrms into a 10 kΩ load per IEC 61938

Timecode Input (LM100-LTC version)

BNC female, unbalanced, per SMPTE 12M-1999

RF Input (LM100-NTSC version)*

F-type female connector with internal 75Ω termination; tuner frequency range: 55.25–801.25 MHz; supports BTSC encoded stereo signals
Selectable CATV or “off-air” modes; CATV mode supports the Cable Television Channel Identification Plan per EIA 542 (user-selectable: Standard, HRC, or IRC); video output: composite, BNC female

RS-485 Serial Remote Control

Input port 9-pin female D-connector for remote control and software upgrades

Alarm Port

9-pin female D-connector, 0–5 V TTL level; user-definable alarms: input clip detection, modulation overload, loudness above threshold, loudness below threshold (silence), dialnorm threshold, and AES input loss

General Purpose Input/Output Port

9-pin female D-connector, 0–5 V TTL level
Functions include: measurement pause, measurement reset, input source select, channel up/down (LM100-NTSC only), measurement state


*The NTSC input replaces the LTC input on this version.

Core Measurement Algorithm (User Selectable)

EBU R128
ITU-R BS.1770-2
ITU-R BS.1770-1

Dialogue Intelligence Algorithm

Proprietary; patent pending

Audio Sampling Rates

32, 44.1, and 48 kHz

Measurement/Analysis System Log

480 events stored in internal nonvolatile RAM
Unlimited event storage and retrieval with use of LM100 software remote application on a PC

Power Requirements

90–264 VAC, 50–60 Hz, auto-sensing, 15 W maximum; designed to operate from a centrally switched power source

Dimensions and Weight

1-U rackmount: 44 × 483 × 375 mm (1.75 × 19 × 14.75 inches)
Net: 2.5 kg (5.5 lb)

Environmental Conditions

Operating: 0°C–50°C (32°F–122°F), natural convection cooling, 0%–98% relative humidity (noncondensing)
Nonoperating: –20°C to +70°C (–4°F to 158°F)

Regulatory Notices

North America: This unit complies with the limits for a Class A digital device pursuant to Part 15 of the FCC rules and Industry Canada ICES-003 Class A requirements. It is UL Listed for the US and Canada.
Europe: This unit complies with the requirements of Low Voltage Directive 73/23/EEC and EMC Directive 89/336/EEC and carries the CE marking accordingly.

Choose from the drop-down menus below to get Dolby professional reference material.