[3D Audio] Pure Stereo 3D Audio™

Pure Stereo 3D Audio^™or ("Pure Stereo" for short) is a recent breakthrough in audio technology (licensed by Princeton University) that yields unprecedented spatial realism in loudspeakers-based audio playback allowing the listener to hear, through only two loudspeakers, a truly 3D reproduction of a recorded soundfield with uncanny accuracy and detail, and with a level of high tonal and spatial fidelity that is simply unapproachable by even the most expensive and advanced existing high-end audio systems.


3D Audio Demonstration for 2 speakers. (Please place yourself in the middle of the speakers)



This is quite impressive and probably will be the future of 3D audio. In the paper at this link there is a very good introduction to Pure Stereo 3D Audio™. I did a resume of it in the following lines:


How does Pure Stereo work?
When the stereo recording is played through the two loudspeakers of a standard stereo system, the ILD and ITD cues are largely corrupted because of an important and fundamental problem: the sound recorded on the left channel, which is intended only for the left ear, is heard by both ears. The same applies to the sound on the right channel. Consequently, an audiophile listening to that recording on standard stereo system will not correctly perceive the musician to be standing on the extreme right of the stage but rather at the location of the right speaker.
In order to insure the correct transmission of the ILD and ITD cues to the brain of the audiophile, the sound from the left loudspeaker to the right ear, and that reaching the left ear from the right loudspeaker (called "crosstalk") should be cancelled.
Pure Stereo is based on a breakthrough in XTC (technique of crosstalk cancellation) filter design, that allows producing optimized XTC filters, called BACCH fi lters, that add no coloration to the sound for a listener in the sweet spot . Not only do BACCH fi lters purify the sound from crosstalk, but they also purify it from aberrations by the playback hardware in both the frequency and time domains.
The result is a 3D soundstage with a striking level of spatial and tonal fidelity never experienced before by audiophiles.


Does Pure Stereo require special room treatment?
Abating room reflections with physical room treatment (i.e. using sound absorbers on sound-reflective surfaces) in a listening room is always beneficial to any audiophile-grade sound system. For Pure Stereo the efect of sound treatment is equivalent to using loudspeakers with high directivity. The more directive the loudspeakers are, the less sound treatment is needed for Pure Stereo to produce a full and accurate 3D sound image.Therefore, in a reflective untreated listening room, directive loudspeakers are more desirable. In a well treated listening room with sound-absorbing surfaces,any loudspeakers, even omnidirectional ones, will produce an excellent 3D image.

Does Pure Stereo require sitting in a sweet spot?
Like for standard stereo, where serious listening requires the audiophile to sit in an optimal location called the sweet spot, Pure Stereo also has a sweet spot.
However, unlike standard stereo, where the sweet spot must be at a given location and in a vertical plane that is exactly equidistant from the two loudspeakers, the sweet spot of Pure Stereo can be designed to be anywhere in the listening room, because the Pure Stereo filter can compensate for any asymmetries in the listening configuration.
The Pure Stereo sweet spot is large and robust enough so that a listener sitting in it perceives a high-fidelity 3D image without having to strain to keep his head in a fixed position.

Does Pure Stereo require special positioning of the loudspeakers?

While Pure Stereo filters can be readily designed for a pair loudspeakers and a sweet spot in an any geometric configuration (including the standard stereo triangle configuration), it is highly recommended that the loudspeakers be positioned in the so-called \stereo dipole" configuration, which typically has the loudspeakers about 50 cm apart only.

Is the 3D realism of Pure Stereo the same with all types of stereo recordings?
The stereophonic recording technique that is most accurate at spatially representing an acoustic sound field is, incontestably, the so-called "binaural" recording method, which uses a dummy head with high-quality microphone in its ears. Until the recent advent of Pure Stereo, the only way for an audiophile to experience the spectacular 3D realism of binaural audio was through headphones.
Pure Stereo shines at reproducing binaural recordings through two loudspeakers and gives an uncannily accurate 3D reproduction that is far more stable and realistic than that obtained by playing binaural recordings through headphones.


How does Pure Stereo differ from other 3D audio techniques?
High order ambisonics (HOA) and wave eld synthesis (WFS) are two other techniques for 3D audio over loudspeakers. They are presently being developed by a number of research groups and can, in principle, reconstruct an approximation of a recorded 3D sound eld over a relatively large area (larger than the sweet spot of crosstalk cancellation techniques). However, unlike Pure Stereo, they require a large number of loudspeakers for playback.
Moreover, unlike Pure stereo, both HOA and WFS are incompatible with stereo recordings as they require highly specialized recording techniques involving a large number of microphones.

I let you with a Video explaining what is Pure Stereo 3D Audio™ by the words of it's inventor Professor Edgar Choueiri 

References:
[Studio360 website] http://www.studio360.org/2011/apr/29/adventures-3d-sound/
[3D3A website] http://www.princeton.edu/3D3A/index.html
[Pure Stereo 3D Audio™ Paper] http://www.princeton.edu/3D3A/Publications/Pure%20Stereo.pdf