A new 3D audio technology has been in the news recently. What's notable about this latest approach is that it works with stereo loudspeakers - not headphones - for proper playback and can be used to enhance existing stereo recordings.
The technique, developed by Edgar Choueiri, a professor of applied physics and aerospace engineering at Princeton University, uses optimized crosstalk cancellation filters to allow binaural cues in a recorded signal to reach a listener's ears with minimal degradation. During normal (non-filtered) playback of binaural sound through loudspeakers, these spatial cues are significantly degraded as a result of the crosstalk that exists between the respective loudspeakers and listener's ears.
This approach appears to offer advantages over other loudspeaker-based 3D audio techniques (such as ambisonics and wavefield synthesis) as it requires only two loudspeakers for playback and is compatible with existing stereo recordings. In fact Choueiri claims that crosstalk cancellation will "significantly benefit the realism" of such recordings, since most contain significant binaural cues.
Of course, there's no such thing as a free lunch and most audiophiles will no doubt cringe at the thought of adding extra circuitry - especially crosstalk cancellation filters, which have a reputation for adding significant spectral coloration to the sound - into their audio playback system signal path. However, Choueiri, an audiophile himself, claims that his processing technique was developed with that concern in mind and that it adds nothing artificial to the sound.
Implementation in an end-user audio system is achieved through a digital processor unit that applies - in real time - a customized digital filter to any stereo sound input. The filter is created using on-site, in-position acoustic measurements of the entire listening chain and recordings made from miniature microphones placed at the entrance of the listener's ear canals.
This technique isn't limited to consumer in-home audio system use. Other applications mentioned include 3D audio for 3D TV and 3D cinema, as well as advanced hearing aids.
An interesting short (6:44) video - "Introduction to 3D Audio with Professor Choueiri" - is available on the home page of Choueiri's 3-D Audio and Applied Acoustics Laboratory web site. The video includes animations demonstrating the 3D audio technique, as well as some actual 3D audio demos. (Check out the buzzing fly!)
Other resources include a technical paper on Optimal Crosstalk Cancellation for Binaural Audio with Two Loudspeakers and a list of 20 Questions and Answers about Pure Audio, the name under which the technique is licensed. Also, an experimental survey on loudspeaker directivity - a key related loudspeaker property - includes measured directivity data for a number of loudspeakers.