Background

To deliver Dolby Atmos and other new audio experiences, the broadcast industry needs audio technology that provides a smooth transition from traditional stereo and 5.1 channel workflows using existing infrastructure.

Dolby ED2 is an extension to the Dolby E codec to support immersive audio, as well as to provide new tools to solve audio production issues. Dolby ED2 is backward compatible with Dolby E-capable pass-through and decoding products to allow broadcasters to integrate next generation audio using existing contribution encoders, decoders, routers, and monitoring tools.

Key Features and Benefits

Dolby ED2 is an extension to the proven Dolby E mezzanine audio codec and enables the carriage of immersive audio and metadata. While Dolby E supports surround sound audio and the carriage of multiple streams, it does not have the extensions necessary to carry Dolby Atmos audio, loudness information, and other important metadata. Dolby ED2 extends Dolby E to introduce a new metadata system and provides the ability to package and synchronize multiple Dolby ED2 substreams to carry more audio. To minimize outboard equipment and to guarantee sample accurate channel alignment, all Dolby ED2 decoders and transcoders have inbuilt sample-accurate multi-stream frame synchronizers as standard. A new metadata framework provides carriage of the metadata required to deliver immersive audio experiences alongside existing audio formats in the same professional broadcast workflow.

Figure 1. Example layout of audio elements and metadata before encoding

 

Key Features • Next generation audio mezzanine codec designed for SDI infrastructure and satellite backhaul • Backward compatible with Dolby E pass-through and decoding products • Supports up to 16 audio channels with 8 channels carried per Dolby ED2 substream on a single AES3/SDI audio pair • Provides new metadata to manage immersive audio and rendering to existing formats

 

 

Dolby ED2 is backward compatible with Dolby E-based products. Any product that supports Dolby E pass-through will also support Dolby ED2 pass-through. In addition, any existing product that can decode Dolby E can also decode the audio elements and Dolby E-compatible metadata in a Dolby ED2 stream. Products that implement Dolby ED2 will understand the topology of a Dolby ED2 bitstream and can:

• Render complete audio presentations

• Actively process audio elements

• Perform loudness compliance

• Support full metadata status and diagnostic analysis

Bitstream Topology

Dolby ED2 builds upon Dolby E where each bitstream carries a maximum of 8 channels of audio. Dolby Atmos requires the carriage of more than 8 channels of audio. For example, a Dolby Atmos immersive audio presentation may be delivered as 5.1.4 or 5.1.2 channel-based audio, or as many audio objects with three-dimensional positions, or a combination of both channels and objects. Dolby ED2 supports these higher channel counts by providing metadata that describes the topology and synchronization of each audio presentation that is distributed across multiple Dolby ED2 substreams. This functionality allows for higher channel count audio to be sent via bandwidth constrained satellite or fiber contribution links in a compressed format with guaranteed, sample-accurate alignment on reception.

Metadata Carriage

Dolby ED2 is capable of delivering new immersive experiences, not previously possible with Dolby E, through a new metadata format. This metadata can be categorized as follows:

• Audio stream structure

• Description of audio elements

The audio stream structure is described by identifying a collection of audio elements that are either audio objects or beds. Objects are mono sources whereas beds describe an audio scene with a conventional channel-based layout. Audio object element descriptions provide the location of the object and other details for binaural rendering or VR usecases. Audio bed elements descriptions specify the layout of the bed and the gains of the individual channels. The metadata is carried alongside the audio essence in a frame-based structure that supports real-time switching of streams like Dolby E.

Figure-2. Basic structure of Dolby ED2 with Metadata

Dolby ED2 in Live Workflows

From the audio mixing console, the program music/effects, dialogue objects, and other audio elements are input to a Dolby ED2 encoder as independent audio channels. The Dolby ED2 encoder, in conjunction with an object-based audio authoring tool, encodes the audio and generates metadata parameters, e.g., audio object positions and audio presentations. The encoder outputs a Dolby ED2 stream for contribution delivery.

Existing contribution encoders and integrated receiver-decoders (IRDs) that support Dolby E will support Dolby ED2 so long as the encoders support multiple pairs of Dolby E for contribution. The efficiency benefits of Dolby ED2 allow conventional stereo and 5.1-channel presentations to be delivered alongside object-based audio presentations for redundancy and multi-format delivery.

At a broadcast head-end, Dolby ED2 can be decoded into PCM with Serial ADM to support uncompressed SDI or IP audio workflows. Dolby ED2 can be recorded or played out for live-to-file or file-to-live use cases. For emission, Dolby ED2 can be transcoded into a next generation audio format such as Dolby Digital Plus with Dolby Atmos or Dolby AC-4 for efficient consumer delivery.

 

Figure-3. Dolby ED2 Live Workflow

Dolby ED2 Monitoring

Dolby ED2 decoders provide full monitoring capabilities for the multiple audio presentations and metadata in a Dolby ED2 stream. A Dolby ED2 decoder can render immersive, surround, and stereo presentations of the carried audio. The backward compatibility of Dolby ED2 allows a Dolby E decoder in an existing contribution/distribution chain to provide basic audio metering and confidence monitoring of a Dolby ED2 stream.

Conclusion

Dolby ED2 provides a low-friction path to integrating next-generation audio into existing live/linear workflows. The efficiency of Dolby ED2 allows it to be carried alongside existing stereo and 5.1-channel audio for redundancy and multi-format delivery. The backward compatibility of Dolby ED2 allows it to be transmitted, received, and decoded by a large install-base of Dolby E decoders. Professional metadata defines new parameters to specify audio topology, describe presentations, and improve loudness control. Dolby ED2 provides the foundation for state-of-the-art, scalable next-generation audio solutions for authoring and contribution of live and post-produced content.

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