AAC Metadata

Audio-specific metadata play a significant role in controlling program loudness, dynamic range and downmixing of the broadcast audio bit stream. With MPEG-4 AAC and HE-AAC now being a popular choice for digital broadcasting services worldwide, the importance of loudness-related metadata as a standardized feature of these codecs becomes even more relevant when the requirements of program loudness normalization are taken into account. One requirement is that the audio of TV commercials have the same loudness than the TV program they accompany. The MPEG AAC formats natively support all required metadata parameters (e.g. for loudness control) included in professional audio codec and broadcast systems. In addition, Fraunhofer IIS offers implementations for transcoding of existing and generation of new metadata.

Loudness Normalization

The Dialogue Normalization is used to adjust and achieve a constant long-term average level of the main program components across various program materials, e.g., a feature film interspersed by commercials.

Dynamic Range Control

The Dynamic Range Control (DRC) facilitates control of the final dynamic range of the audio and adjusts compression to suit individual listening requirements.

Downmixing

The Downmix maps the channels of a multichannel signal to the user`s mono or two-channel stereo speaker configuration.

Loudness control regulations, such as the recent CALM Act (Commercial Advertisement Loudness Mitigation), are being put in place to address consumer complaints about disturbing loudness differences between TV programs and commercials. AAC family of audio codecs, including AAC and HE-AAC, offer the ability to carry the original broadcast metadata to meet the requirements of the CALM Act and other legislative/regulatory loudness specifications e.g. EBU R128, D-Book and others.

Metadata allows broadcasters and service providers considerable control over how the original program material is reproduced for the listener. With Fraunhofer IIS Audio Metadata Transcoding Technology, it is possible not only to create new AAC metadata streams, but also to convert existing metadata to the AAC format.

The AAC Metadata Technology is available for all Fraunhofer HE-AAC en- and decoders. Optionally the AAC Encoder can be supplemented with the Fraunhofer IIS Audio Metadata Transcoding Technology.

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