David Farnor | On 06, May 2017

This weekend, a special binaural version of Doctor Who will be released on BBC iPlayer.

Knock Knock, Episode 4 of Season 10, will be broadcast on BBC One at 7.20pm as usual. When the episode arrives on the Beeb’s catch-up service, though, a remixed version of the episode will also be available to stream.

What is binaural sound? It’s a more immersive way of listening to things. The traditional stereo format is designed to create a frontal sound stage on a pair of loudspeakers, but when listened to on headphones it gives a very different image. Binaural techniques, though, make it possible for sounds to appear to come from a point in space outside of the head. Instead of the simple left-right amplitude panning of stereo, it uses the way the brain recognises and locates sounds to position sounds on a 3D plane (front and behind, above and below), creating a virtual acoustic sound scene around the listener.

“This is not a new concept, it was heavily developed by researchers in the 1990s when virtual reality technology was a hot topic,” explains Chris Pike, Senior Scientist in the BBC Research & Developmen’s Audio wing.

With VR on the up once more, it’s only natural that binaural should be explored once again. BBC R&D has developed tools at BBC Wales in Cardiff to explore and find new ways to use the technology for the broadcaster’s work.

“We believe it can offer BBC audiences a more immersive and engaging experience. We are developing the technology for spatial audio over both loudspeakers and headphones, but for headphones the opportunity to improve things seems particularly strong right now,” adds Pike.

Indeed, with mobile devices and other equipment increasingly used to watch programmes on BBC iPlayer, more and more people are listening to BBC content with headphones.

So how does Doctor Who come into it? In 2015, the BBC released the Fright Night binaural audio drama Ring, with Cathy Robinson working on the sound. On the back of that, BBC R&D were able to show their work to the show’s team, leading to the series deciding to use it for Knock Knock.

The episode in question guest-stars David Suchet as the sinister landlord of a spooky house-share that the Doctor’s companion, Bill, moves into.

“The sounds of the house are definitely paramount here,” we wrote in our spoiler-free review of the episode. “The real business here comes with Murray Gold’s score, his best work of the season so far, and the way in which the noises of the house “settling” heighten the tension throughout the episode… [It’s] well worth listening to on the best speakers possible.”

Robinson and Pike worked with dubbing mixer Darran Clement to remix the episode, working from the surround sound loudspeaker version used for the HD TV broadcast.

“Darren did a fantastic job of enhancing the spatial impression for the binaural mix, giving a more natural sense of the space of the environments and movement of the characters,” says Pike. “In this mix we used an approach often called ‘bed plus objects’, where much of the sound is mixed to a virtual 3D loudspeaker array (the bed) and then certain key sound effects are processed as separate objects within the scene. This has the benefit of speeding up the mixing process, partly due to compatibility with existing production tools such as reverb and dynamics effects. Whilst the tools for spatial positioning are working well, there’s still a long way to go before all of the tools in a sound engineers toolbox support spatial audio.”

In the future, the BBC’s R&D team hope that in the future, when you plug headphones in on BBC iPlayer, you’ll automatically get a binaural version, using the same mix as the surround sound loudspeaker version. For now, a chilling episode of Doctor Who will have to do.

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