Dolby Metadata

Dolby Audio Metadata

Dolby® audio metadata gives you a powerful—and simple—way to ensure the best audio quality for your customers, regardless of the playback device and environment. It gives you control over essential signal parameters, including the critical three Ds: dialogue normalization, dynamic range, and downmixing.

Metadata is data about the data. More precisely in broadcasting, it’s descriptive data that accompanies the audio program. It enables broadcasters and operators to deliver audio that sounds just the way they want, whether their viewers listen in full surround, stereo, or mono. Dolby audio metadata specifies key program parameters for all downstream processing—including the final transmission to consumer decoders—and enables the delivery of exciting, dynamic surround sound and more compressed, uniform stereo sound within a single audio stream.

If you’re working in production or postproduction, metadata gives you the means to ensure that consumers hear the program as you intended, no matter what equipment they’re using.

In transmission applications, metadata lets you monitor and QC program parameters and correct any erroneous settings. At the playback end, metadata instructs TVs and set-top boxes (STBs) on proper loudness control, allows configurable dynamic range modes, and specifies downmixing parameters when necessary.

Integrating Dolby Metadata in Your Workflow

All Dolby Digital Plus and Dolby Digital transmissions include metadata. However, there are several approaches for setting metadata; these vary depending on the degree of control required and the diversity of program genres to be transmitted.

At the simplest level, a single preset of metadata can be chosen to suit the audio style of the channel and applied in the transmission encoder. This can work acceptably where all programs are of a single genre and where the audio is prepared in a uniform way—for example, where programs already have consistent loudness. Where this is not the case, some method of setting metadata on a program-by-program basis is advisable. This can be achieved through genre-based presets, but ideally metadata should be set at ingest and carried with the content.

Basic Workflow

In the basic workflow, metadata is:

Set at the content ingest

Carried alongside the multichannel audio program content through the infrastructure

Encoded into the delivery codec at the final transmission point

Extracted by the consumer playback decoder in the TV or STB

Metadata can be carried alongside audio using a number of methods—for example, as a separate data file or serial data stream, or packaged together with the audio as Dolby E.

Workflow with Dolby E

Dolby E is a professional audio coding system capable of carrying up to eight channels of 24-bit audio and its metadata through a two-channel broadcast infrastructure. The metadata carried in Dolby E can interface directly with Dolby Digital Plus or Dolby Digital.

Dolby E is very robust and can be encoded and decoded multiple times through the broadcast chain with no audible degradation. All elements of a Dolby E bitstream are locked together so that the metadata and audio always maintain their timing relationship. Dolby E bitstreams are video frame–based, with a complete metadata set encoded into each frame.

Dolby E can be embedded into HD-SDI and also carried inside BWAV, MXF, and MPEG-2 transport streams.

Alternatives to Dolby E for Dolby Metadata Insertion and Carriage

Serial metadata, SMPTE RDD 6; video frame–based

VANC metadata, SMPTE 2020

DMDB Chunk, EBU Tech 3285 Supplement 6; storage within BWAV

XML

MXF, SMPTE 382, and SMPTE 380 DMS-1

Transport Stream, SMPTE 2038, and SMPTE RDD-11

See the Working with PCM tab for more detail on Dolby E alternatives.

Partner Products for Working with Dolby E and Dolby Metadata

Many of our partners manufacture equipment that can encode, decode, pass through, and analyze Dolby E and Dolby metadata.

Key Dolby Metadata Parameters

Consumers' listening systems vary widely, from full multichannel home theaters to conventional stereo to mono TVs. Dolby metadata provides a number of key parameters designed to give consumers the optimal sound for any program, no matter the listening system.

These key parameters are the three Ds:

Dialogue normalization

Dynamic range control

Downmixing

Proper setting of the three Ds offers a simple and easily used method that provides the best quality sound reproduction without regard to the number of speaker channels, ambient noise levels, or playback equipment quality.

Dialogue Normalization

The dialogue level parameter, known as dialogue normalization or dialnorm, provides a loudness level normalization value to the home decoder. Dialnorm helps in level-matching between programs or between media.

Dialnorm measures average program loudness based on speech, rather than signal peaks. The loudness value is measured (referenced to dBFS using an algorithm such as ITU-R BS-1770) and carried by Dolby Digital Plus directly to a home’s STB or TV.

Setting dialnorm is simply a matter of monitoring program loudness with a dedicated loudness meter and entering that loudness level within the metadata stream. Alternatively, you can mix the program to achieve the target loudness level on the meter.

Dynamic Range Control

Dynamic range control (or dynamic range compression, DRC, or “midnight mode”) allows the consumer to listen with a reduced dynamic range. This lets viewers watch TV without disturbing neighbors or others in the household. (The control is optional on consumer equipment.)

The dynamic range control essentially raises the level of softer program portions while lowering the level of loud segments. The listener can hear everything without having to continually reach for the volume control.

The dynamic range control in Dolby metadata involves two parameters, RF mode and Line mode.

RF mode:

Matches the delivery of conventional analog broadcasts

Closely approximates dynamic range levels of DTV with MPEG stereo audio

Includes a level shift that boosts the audio by 11 dB

Line mode:

Provides lighter compression

Allows user adjustment of low-level boost and high-level cut

Before setting dynamic range values, you need to select the appropriate dialnorm value. You then preview the source mix before choosing a dynamic range preset.

Downmixing

Downmixing is a feature of Dolby Digital Plus (and Dolby Digital) that allows a multichannel program to be reproduced by fewer speakers. Viewers do not need a 5.1-channel system to enjoy a digital TV broadcast.

The downmixing parameter lets you adjust the levels of the surround and center channels that are mixed into the stereo outputs. You have considerable flexibility in making surround sound work effectively in stereo.

Stereo output can be of two types:

A stereo-compatible Lt/Rt downmix suitable for Dolby Pro Logic® decoding

A simple stereo Lo/Ro downmix for stereo hi-fi or headphones

Specific parameters also allow you to select which stereo analog signal is preferred as the default. Other, separate parameters adjust the Lo/Ro and Lt/Rt downmix conditions.

Using Presets

Metadata can be set for each specific program. Dolby also provides genre-specific presets optimized for various program types. It’s important that you consider which presets to use.

Another consideration in choosing metadata is the delivery specifications set by downstream operators, who may require specific presets.

See our Settings tab for charts with typical presets.

Equipment

Dolby offers a number of solutions to help in setting metadata.

Dolby’s solutions for automated, non-real-time control:

Dolby DP600 Program Optimizer

Dolby Media Emulator software

Dolby’s solutions for real-time metadata generation and emulation:

Dolby DP570 Multichannel Audio Tool

Dolby Media Emulator software

Our partners also offer a wide array of hardware and software.

Assistance

We offer extensive training resources. Please contact a Dolby representative for details. We also have a network of full-service consultants who can provide everything from training to turnkey operations. Additionally, you can contact our partners for advice and products for metadata carriage.

For facilities not using Dolby E, working with Dolby metadata and PCM presents few obstacles in today’s broadcast environments. All metadata formats used in the professional environment will achieve the same degree of controlled audio optimization in the consumers’ homes. And all of the methods are standardized, offering identical behavior to the equivalent Dolby E systems.

Workflow Considerations: Adding Channels, Integrating Metadata

Many professional systems already have the capacity to handle multichannel PCM audio and metadata. The transition from stereo PCM is very easily accomplished, with many options for carrying metadata alongside the audio. Adding multichannel audio does not necessitate removal of the stereo audio, which may be required for legacy SD service. In fact, the 16-channel–capable HD-SDI signal can accommodate many combinations of audio channels, including multiple language or audio description services.

Working with File Containers: Flexibility, Speed, and Partner Support

HD broadcasting is often married with smarter workflows in the professional headend. This brings increased capacity and speed that is fully supportive of multichannel PCM audio. MXF, BWAV, and XML all bring benefits in workflows and allow metadata to be handled in a way that suits specific applications, such as NLE stations or transmission encoding.

Working with HD-SDI: Some Considerations and Best Practices

The same best practices that apply to stereo broadcasting—for instance, timing relationships between channels or A/V sync—also apply to multichannel broadcasting. Many professional monitoring units now offer these analyses. Additionally, many current HD-SDI embedders, de-embedders, and other processing units transparently pass or process the embedded PCM audio.

Reference Specifications

Visit these sites for current reference specifications:

SMPTE

EBU

Please see below for examples of Dolby metadata settings for various types of content.

Extended bitstream information parameters are in italics.

Parameter

Cinema Production

Drama

Documentary

Music

Live Sport

Dialogue level

–27

–23

–23

–23

–23

Channel mode

3/2

3/2

3/2

3/2

3/2

LFE channel

Enable

Enable

Enable

Enable

Enable

Bitstream mode

Main Complete

Main Complete

Main Complete

Main Complete

Main Complete

Line mode pro

Film Standard

Film Light

Film Light

Music Light

Film Light

RF mode pro

Film Standard

Film Light

Film Light

Music Light

Film Light

RF overmodulation protection

Disable

Disable

Disable

Disable

Disable

Center downmix level 

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB)

Surround downmix level

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB)

Dolby Surround mode

N/A

N/A

N/A

N/A

N/A

Audio production information

Yes

Yes

Yes

Yes

Yes

Mix level

105 dB

85 dB

85 dB

95 dB

85 dB

Room type

Large

Small

Small

Small

Small

Copyright

Yes

Yes

Yes

Yes

Yes

Original bitstream

Yes

Yes

Yes

Yes

Yes

Preferred
stereo
downmix 

Lt/Rt

Lo/Ro

Lo/Ro

Lo/Ro

Lo/Ro

Lt/Rt center downmix level

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB) 

0.707
(–3 dB) 

0.707
(–3 dB) 

Lt/Rt surround downmix level

0.707
(–3 dB)

0.707
(–3 dB) 

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB)

Lo/Ro center downmix level

0.707
(–3 dB)

0.707
(–3 dB) 

0.707
(–3 dB)

0.707
(–3 dB)

0.707
(–3 dB) 

Lo/Ro surround downmix level

0.707
(–3 dB)

0.707
(–3 dB) 

0.707
(–3 dB)

0.707
(–3 dB) 

0.707
(–3 dB)

Dolby Surround EX mode

Not Indicated

Not Indicated

Not
Indicated

Not Indicated

Not Surround EX

A/D converter type

Standard

Standard

Standard

Standard

Standard

DC filter

Enable

Enable

Enable

Enable

Enable

Lowpass filter

Enable

Enable

Enable

Enable

Enable

LFE lowpass filter

Enable

Enable

Enable

Enable

Enable

Surround 3 dB attenuation

Enable

Disable

Disable

Disable

Disable

Surround phase shift

Enable

Enable

Enable

Disable

Enable


 
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