3D sound experiments carried out by BBC R&D engineers

By Nicholas Tufnell

Technology reporter

Headphones can give the inaccurate impression that sounds are coming from inside the head

Thanks to the ubiquity of mobile devices, millions of people use headphones to listen to their favourite music, radio shows and TV programmes.

But headphones can give the inaccurate impression that the sounds are coming from inside your head, rather than around it.

To address this, the BBC's Research and Development team is developing new tools for the creation and delivery of binaural audio - a production technique that mimics natural hearing cues created by the head and ears.

In the most recent experiment, the researchers borrowed 10 members of the BBC Philharmonic orchestra last month and surrounded them with a multitude of microphones - placed at different distances and heights from the musicians - to record new raw material to play with.

The BBC played the same pieces several times to simulate different recording scenarios

The advantage of the binaural recording technique is that it can be used to create a richer sense of space, allowing for a more realistic, three-dimensional experience.

Unfortunately current binaural systems, according to the research team, have quality issues that do not allow the audio to be adequately scaled up to a broadcasting standard - at least, not yet.

Dummy heads

One binaural recording technique is known as "dummy head" recording, which involves fitting a dummy with tiny condenser microphones.

The microphones are placed within a dummy's ears to preserve something known as head-related transfer functions (HRTFs).

HRTFs are the variations in sound frequency that are caused by the surrounding structure of the ear, head and shoulders.

But the dummy head technique has become unpopular because of "reasons of quality and practicality," says Mr Pike.

Instead, a more convincing 3D impression can now be achieved by using software to alter six-channel surround-sound recordings - the kind used by 5.1 home audio systems.

Once HRTFs are applied to the captured signals, no special equipment - apart from a pair of headphones - is needed to listen to the result.

However, a "hot area of research" is the addition of a head-tracking device to allow a listener to turn and tilt their head to change their perspective of the audio.

Microphones are placed within dummy ears to help create 3D sound recordings

'Virtual audio reality'

The BBC is far from being the only organisation to experiment with the technique in recent years.

Most famously, the Barber's Haircut video, created by audio software developer QSound Labs in 1996, has amassed nearly 17 million views on YouTube.

Elsewhere, many companies have been releasing binaural sound products, including Fraunhofer, Dolby, and DTS.

There have already been several full-length recordings at the BBC that took advantage of the technique, including the Nine Lessons and Carols concert and a radio drama called Private Peaceful.

In both these programmes, the content was created by converting existing loudspeaker surround sound signals to a binaural signal.

Feedback on these early experiments was positive, eventually prompting Radio 1 to record a show in 3D, an experience that some listeners called "spooky".

             Binaural audio is a production technique that mimics natural hearing cues

Sexing up the sound

"The 3D Sound tag is the usual meaningless marketing nonsense, to sex up the impression of binaural sound," says Hugh Robjohns, technical editor of Sound On Sound magazine, who is not impressed with the technique's re-emergence.

"Binaural stereo is one of those ideas that resurfaces every decade or so, and everyone gets excited about the rediscovery, before getting frustrated and bored with its inherent compromises and imperfections."

Mr Robjohns says while the technique can create spatial effects, it fails to deliver precise and natural soundscapes.

Additionally, he claims binaural recordings do not translate well to stereo loudspeakers.

"The imaging is very vague and the sound can become highly coloured, so it becomes difficult to satisfy both potential audiences, and complaints are not uncommon," he says.

Andy Jones of MusicTech magazine adds that consumers have given the cold shoulder to other claims of increased audio immersion.

"Super Audio CD was supposed to bring surround sound to the masses and replace CD," he says.

"But the mass market doesn't seem to have the appetite for it."

While binaural audio is not a new idea, bringing it to a broad range of broadcasts is unexplored territory.

And the BBC R&D team has another trick that could aid its appeal.

The engineers are experimenting with integrating sound captured via smartphones and tablets into their output. The idea is that members of the public could upload their own audio to enhance professional coverage of live events.

The BBC is experimenting with using consumer devices to enhance binaural recordings

However, Mr Robjohns has one final warning.

"There are actually quite serious potential health and safety risks involved," he says.

"The sound of someone apparently striking a match right behind your left ear can be extremely unsettling and cause people quite literally to jump, which is not a good thing if you're riding a bike or stood on a tube train platform at the time."

Binaural is still in its infancy at the BBC in terms of broadcast output.

But if progress continues to be made, 3D audio might yet succeed where 3D video has struggled - just don't listen to Tech Tent on your bike.

Binaural broadcasting

• Binaural recording is a method of capturing sound that uses two microphones to record "3D" stereo audio
• Such spatial audio, it is claimed, can sound like a more accurate representation of the real world
• Binaural sound itself is not a new idea - a rudimentary form of binaural stereo dates back to 1881.

"There are lots of potential applications for binaural sound and when done really well it's very convincing”

Chris PikeSenior scientist, BBC R&D