‘Audibility’ Could Be Object-Based Audio’s ‘Biggest Win,’ Says BBC Technologist
Much of the recent talk about immersive, object-based audio for next-generation DTV systems like ATSC 3.0 has dwelled on enhanced surround sound to complement pristine Ultra HD pictures. But a somewhat overlooked benefit of immersive broadcast audio will be the opportunity for radio listeners and TV viewers to balance the level of speech against background audio to suit personal taste, the BBC’s technology point man told a London meeting last month of the International Moving Image Society.
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For broadcasters, "audibility" could well become the “biggest win” from object-based immersive audio, said Simon Tuff, BBC principal technologist. “The population is aging and people suffer from age-related hearing loss,” said Tuff. “One of the most common complaints is that music is too loud for speech, or stadium noise drowns the commentary. Unlocking dialogue is very important. The BBC takes this very seriously and you can expect to see a solution based on object-based audio very soon.”
The essence of object-based audio is much like that of multi-track recording, in which the sounds of individual instruments, voices or musical effects are captured separately, said Tuff. Metadata in the digital bit stream of the recording can be manipulated to instruct a capable receiver how to mix and play those individual components according to preset rules or individual listeners’ tastes, he said. “It’s not about broadcasters defining the basic technology, it’s already happening now” with systems like Dolby Atmos and DTS:X, he said.
Metadata with digital signal processing lets the receiver render the same object-based audio reproduction “for headphones, or for any number of speakers, even where someone has put all their 5.1 speakers in a row on the bookshelf, which is remarkably common,” said Tuff. One need not have “20 speakers hanging from the ceiling,” he said. Object-based audio “works well with a few speakers or headphones, and you only have to travel on public transport to see how many people are now using headphones,” he said.
To test theory and turn it into practice, the BBC built an immersive audio lab with 34 speakers at its Salford studios near Manchester, England, and an immersive audio test control room at the network's Broadcasting House in London, said Tuff. Everything in the test control room is IP-based and touch-screen-controlled instead of being operable through a more conventional mixing desk, he said.
The public broadcaster also is developing apps that enable object-based audio to be reproduced on mobile devices, said Tuff. PowerPoints of a prototype device shown at the London meeting by Tuff and his team depicted a virtual slider on a player screen that lets the user adjust the balance between foreground speech and background sound or music.
Object-based audio “can be sent in existing radio channels, without extra bandwidth, and be fully backwards-compatible between new and existing stereo receivers,” Tuff said when we asked whether new object-based content would need to be distributed over IP broadband services, rather than via conventional over-the-air broadcasts. Over-the-air tests at the BBC will begin “as soon as possible,” with consumer product availability “likely” to take up to two years, “depending on standards-setting,” he said.
In addition to enhanced audibility through user-defined balance between speech and background sound, object-based audio also will give home theater owners the ability to “curate the audio effect they hear,” said Tuff. That’s why the BBC sees object-based audio as a natural companion to virtual-reality video, he said. It also wants to use it for “venue exploration,” he said. As an example, he said, an orchestral concert can be shot in 4K video and the sound of the individual orchestral instruments captured as separate objects, so a viewer can pan and zoom on the 4K image, and the sound scape automatically mixes to match.