The audio renderer has long been a bone of contention in the standardisation work on Next Generation Audio (NGA), writes EBU Senior Project Manager Roger Miles.
Rather than precisely mapping audio channels in programme production to loudspeaker channels in reproduction, NGA uses a more intelligent method. It assigns audio to appropriate reproduction channels by labelling each snippet or portion of audio programme with metadata containing all necessary technical information needed to reproduce it optimally in the reception equipment.
This allows broadcasters to produce a single audio version for their programme that can include accessibility services and is ready for distribution and reproduction on a whole host of platforms.
To make NGA viable for all potential adopters and end-users it would need to be defined as an open system, free of unexpected licensing and proprietary idiosyncrasies. This has largely been achieved within the ITU by specifying a suitable
64-bit audio file format (BF64), the Audio Data Model (ADM) that defines the metadata necessary, and all the target loudspeaker layouts that have been identified (stereo, 5.1, 10.1, 22.2, etc).
The work in specifying NGA is by no means complete. Issues such as loudness measurement, for example, need addressing and the ADM is being further developed to make it suitable for streaming environments.
And then there’s the renderer. A piece of software buried in hardware or apps, the renderer’s fundamental purpose is to act on the metadata received and to present all the different audio elements and streams to the reproduction hardware. The reception equipment will, via the renderer, make sense of the metadata and will assign audio appropriately to its replay hardware. The renderer will also present many of its variables to the end user, giving the opportunity to ‘mix’ his/her ideal programme by selecting and varying the gain of all the available audio resources delivered.
Broadcasters have little knowledge and next to no control over the listening and viewing environments used by audiences. The only known is that multiple distribution platforms, including satellite, terrestrial, cable, internet and mobile data, and replay devices such as smartphones, tablets, computers, radios, smart TVs, car receivers, home theatre systems are used.
“Broadcasters have little knowledge and next to no control over the listening and viewing environments used by audiences”
It would be impossible to dictate the exclusive use of a known commercial NGA system (and renderer) in this signal chain. The best that can happen is universal access to an open NGA system standardised by an internationally recognised standards body, including a renderer capable of use directly with ADM metadata.
All reception equipment and apps would need to have this ADM renderer available as an option, and/or the proprietary renderers built into the reception equipment would need to readily parse and convert the ADM into an equivalent, proprietary dataset for their processing.
So far, the progress in defining a unique, open, standardised renderer has been marginal. The commercial giants in the audio industry understandably all have their vested interests in defining their own renderer with special adaptations to their own metadata.
Their aim is to achieve a repeatable level of audio excellence and, of course, to consolidate their market share in the new technology. While this approach may be extremely viable in clearly defined vertical businesses such as cinema, packaged media, subscription broadcasting and OTT, for open broadcast, which is by its nature a transversal business, this is not the case.
In March 2018 the EBU published a specification (EBU Tech 3388) for the EBU ADM Renderer: the EAR! It was developed by BBC, France Télévisions, IRT and technology partners to fulfil the needs of broadcasters. In its initial form the EAR is file-based and does not accommodate a complete set of potential audio formats. In the fullness of time its functionalities will be enhanced, and Tech 3388 will be updated.
It has been offered to the ITU for incorporation in its standard and it is hoped that the respective vendors can accommodate the EAR in their commercial systems, as outlined above. It will be demonstrated on the EBU stand 10.F20.