Send for the Doctor
What Hi-fi? (time) travelled to Wales to watch an episode of BBC’S Doctor Who being recorded in binaural audio
“The binaural mix of means your ears are fooled into thinking the sound is coming from all around you, rather than in stereo format from your headphones”
The fourth episode of Doctor Who’s 10th series, titled ‘Knock Knock’, has been released on the BBC iplayer with 3D audio. But what does that actually mean? In films and TV, sound makes all the difference. The tension in a horror film’s high-pitched scream, or the impact of a booming explosion, is nothing without detailed and punchy audio.
But when using headphones it’s hard to feel like you’re in the middle of the action – and this is where a binaural soundtrack comes in. It places sounds above, below and around you, giving the listener a greater sense of immersion.
That’s exactly what the BBC has done with Knock Knock – set in a haunted house, the Doctor (played by Peter Capaldi) and his assistant Bill Potts (Pearl Mackie) are fighting an unusual adversary – a plague of extraterrestrial insects that live inside the walls of the house. Sounds come from every direction, as the insects scurry around, adding an extra level of realism to the show. Or, at least, it does if you’re watching via iplayer.
What Hi-fi? travelled to Newport, south Wales for an exclusive look at the technology involved in the making of this episode. Here are five things we learned from the experience...
1) It’s immersive
How does binaural recording actually work? Well, the answer is, exactly as normal hearing. The recordings are made for headphone use and the microphones positioned to create a credible soundstage with headphones, rather than a conventionally positioned pair of speakers.
Knock Knock’s binaural mix means your ears are fooled into thinking the sound is coming from all around you, rather than just in a stereo format from your headphones. The creaks of floorboards come from underfoot, while the sound of scurrying in the attic truly seems as though it’s above your head.
2) Binaural recording technology has changed a lot
Binaural recording isn’t exactly a cutting-edge technology – it was first demonstrated in France in 1881 through the Théâtrophone – but the way binaural recordings are made has changed with the advent of computers and algorithms.
In the early 1970s, dummy head microphones were used. These had extra microphones in each ear cavity, and could account for extra variables such as vibrations or the reflection of sound off the shoulders which external microphones wouldn’t be able to pick up on. TOP 5
However, these had a few practical issues. The dummies aren’t easy to transport, and have to be placed in every location where the show is shot – and also moved for every new take.
For a programme such as Doctor Who, that switches frequently between locations, this can be a challenge. Nowadays the BBC’S soundmixing team uses a piece of software called Nuendo to recreate the effect by artificially adding time delays and gain to a number of mono (single-channel) recordings.
3) We’ll see more of it, particularly in dramas
Binaural audio is something the BBC wants to do more often. But making a binaural mix, as well as the stereo and 5.1 surround mix for the standard and high-definition versions, takes more time than a normal recording.
For Knock Knock, adding a binaural soundtrack took approximately a week of work for the team of sound mixers – not something that can be done for each episode.
However, there are ways to cut the timescale down, such as by developing a sound format that can be decoded into stereo, 5.1 surround and binaural depending on your output. By working in one format, rather than two, this could reduce the amount of time it takes to add a binaural mix from a week to as little as a day.
That said, you still won’t hear binaural audio on every type of show. Right now, the focus will be on dramas, or more specifically, the type of programmes with lucrative foreign markets. Having dialogue over a sound effect makes it more difficult to mix binaurally, but drama programmes often have their audio effects recorded separately so that foreign broadcasters can place dialogue in their native language over the top. This means the sound engineer has a cleaner sound to manage.
4) You have to account for people having bad headphones
It’s easy to play a binaural recording in your home or from your phone – all you need is a pair of headphones. But not everyone places the same degree of importance on sound quality. The BBC’S sound mixers, who usually edit using £100 Beyerdynamic DT100 headphones, need to make adjustments to ensure that people listening through the headphones bundled with their smartphone don’t lose out.
For example, LFE (low frequency effects) need to be moved a little higher into the frequency range to account for headphones that won’t pick up on the low bass. Similarly, those expecting high levels of tension from an insightful treble might be disappointed if they aren’t using a sophisticated pair of cans.
The dynamic range is also compressed a little, so that people using smartphones don’t need the volume turned up to potentially eardamaging levels. Ultimately, the more people using better headphones, the better quality we’ll get from binaural sound.
5) It’s perfect for VR television
While binaural audio might reach more people through the BBC iplayer, it is ideal for use with virtual reality. The Beeb has used this tech before, with Google Daydream projects such as Turning Forest, but the numbers of people using VR products (such as Oculus Rift or Samsung Gear VR) remains low. This might change if streaming services such as Netflix take steps towards VR programming, but so far its efforts are minimal.
In future, we may also be able to get binaural audio without wearing headphones, using head-tracking software to monitor a listener’s movements, but progress is slow, particularly with the complexities of catering for multiple people listening in one room. So for now, the closest thing you’ll get to immersive audio without headphones is still Dolby Atmos.