One unexpected consequence of the mobile revolution is a renewed interest in headphone technology, which is entering a second generation after the first surge of research and development in the 1960s and 1970s on the back of stereophonic audio systems.
This time round, though, it is broadcasters, rather than producers of sound systems or for that matter mobile operators, that seem to be taking the lead.
The first generation was all about hi fidelity and audio quality, aiming to exploit the stereophonic separation of sound through very clear reproduction in each of the two head pieces. But, this time, the focus is not so much on the audial impact, which is already at a high level on even modestly priced headphones, but in harnessing sound more closely to the video to improve the overall audio-visual experience, as well as enhance special effects. The focus now is on the sound production itself rather than on the headphone hardware, through technology known as "binaural sound," that is surround sound dedicated to delivery over headphones.
This was discussed at a recent EBU workshop on "Immersive Audio over Headphones," comprising 3D audio experts and practitioners. This had nothing directly to do with 3D TV, though, since the technology will be equally applicable to conventional TV display. Like so many ideas, it has been around for decades. But, it is now deemed feasible as a result of progress in signal processing, as well as better understanding of the role in sound perception of the head and the pinna, which is the visible part of the ear alternatively known as the auricle.
The pinna’s job is to collect sound, amplifying it by acting as a funnel, while also performing spectral transformation to give the brain the information it needs to localize the source. The angle at which sound waves hit the pinna determines the reflections obtained from different parts of the surface, creating phase effects that help identify at least the direction of a sound source if not the distance.
Binaural sound attempts to replicate some of these affects through headphones, creating delays and phases designed to mimic the effect of a particular sound source. If the video was, say, of a person suddenly hearing a lion roar from somewhere behind but a bit to the left, the binaural production aims to mimic that.
One of the challenges is that individual external processing of sound through the pinna depends on the head and ear shape, which, for broadcasters, could represent both a problem and opportunity. Personalized surround sound could be a competitive winner but the question is how to mimic the dynamics of the user’s hearing system. This could be done via a client app, but it remains to be seen how this would be personalized.
That was one of the issues discussed at the EBU conference, along with the implications for content producers, which already have to grapple with 3-D and increasing HD resolutions for video. At any rate, the EBU is now convinced that binaural sound is the next big thing in audio, fueled by the headphone boom.
