Specifications

2
Technology Overview
The Dolby
®
Professional Loudness Metering solution combines the use of standards-based loudness estimation algorithms with Dolby
Dialogue Intelligence™ technology. Supported algorithms are those most prominently in use worldwide: Leq(A), ITU-R BS.1770-1,
ITU-R BS.1770-2, and EBU R 128. These algorithms create a value that can be assigned as the loudness level of a program, using
a combination of tools that include frequency-weighting curves to account for the human ear’s particular sensitivity to audio in the
middle of the hearing spectrum.
In addition to loudness metering, the license program includes support for true-peak measurement. Current peak-metering methods
for digital signals often display only the largest sample value, but the actual peak of the audio signal often occurs between samples.
True peak gives a better indication of actual location of the peak.
The license also includes the ability to measure and correct a wide range of audio streams, including Dolby E, Dolby Digital, and Dolby
Digital Plus, in many cases without the need for separate encoder and/or decoder agreements.
Loudness meters provide a great way to measure the dialogue normalization (dialnorm) value for inclusion in metadata. Meter
products can also verify the dialnorm value in preencoded streams. Both Dolby Digital and Dolby Digital Plus—used for audio
encoding in many broadcast standards around the world—include full support for Dolby audio metadata. At the core of this
metadata is the dialnorm value, which decoders use to adjust the audio content’s replay level in the home. Dolby audio metadata is
implemented in all Dolby Digital and Dolby Digital Plus decoders, such as in TVs, set-top boxes, and A/V receivers.
File-based loudness correction products such as the Dolby Professional Loudness Correction solution perform dual-pass loudness
correction to ensure balanced audio loudness levels without any of the artifacts introduced by real-time correction processes. The
rst pass measures the audio level, and the second pass corrects it, thus fully retaining the content creator’s intent and the original
dynamics of the content.
For more information on loudness estimation algorithms and Dialogue Intelligence, please refer to these publications:
Dolby broadcast loudness solutions overview
ITU-R BS.1770-1 and ITU-R BS.1770-2, Algorithms to Measure Audio Programme Loudness and True-Peak Audio Level
EBU R 128, Loudness Normalisation and Permitted Maximum Level of Audio Signals
For further information on Dolby Digital Plus and metadata, please refer to these publications:
All About Audio Metadata
Introduction to Dolby Digital Plus, an Enhancement to the Dolby Digital Coding System