This is a continuation of the post I started a couple of days ago about the 3D Audio that I experienced in the ballroom next door to the HRA Marketplace at the recent CES 2015 event. You can read the initial installment by clicking here. When I entered the room the setup was as shown in the photograph below:
Figure 1 – The 3D Audio setup prepared by Dr. Edgar Choureiri.
The first thing you notice is the single chair. This is a demonstration for one person in the ideal sweet spot. The two speakers are about 5-6 feet away for the head position of the listener and there is some aggressive baffling on the floor in front of the Barcelona Chair (I guess if you’re going to do a great demo using a classic piece of furniture designed by Mies van der Rohe is a must have rental item).
From a the website I found this statement on the concept behind Dr. Choureiri’s work at Princeton:
“If you ask a room full of people how many have listened to stereo sound through loudspeakers, chances are, everyone will raise their hands. The truth, however, is, that no one has. To faithfully reproduce stereo, the sound source for each channel must be separated. Unfortunately, with conventional two-loudspeakers based audio systems, true stereo cannot be reproduced. Sound from the left speaker ‘spills’ to your right ear and vice versa, resulting in significant crosstalk. On top of that, severe interference and comb-filtering are resulted when the sound from the left speaker meets that from the right speaker. Short of building a wall between the left and right speaker that extends from the front wall all the way to your nose, it seems impossible to avoid this fundamental problem. With crosstalk, your brain is confused by the corruption of information cues, and will not be able to reconstruct stereo images as recorded and intended. Instead of listening to true stereo images, a crosstalk-polluted stereo playback system will only produce phantom images. This fundamental and significant crosstalk problem has plagued two-loudspeakers based stereo playback since day one.”
The following image is included to show the crosstalk created by the two stereo speakers:
Figure 2 – Illustration from the BACCH-SP website showing the crosstalk caused by speakers delivering sound to the wrong ears.
I don’t agree with the statement above. The concept of stereo as first described and implemented by Alan Blumleim in 1931 describes a process of using a pair of microphones (he used omnis at the time but included directional mikes in his patent application) to capture the sound in an acoustic space. The two microphones share many of the same sound sources but have slightly different phase, amplitude, and timbral components. When played back through a pair of headphones (he did refer to his work as “binaural” audio) the idea was to have the listener experience the sound at the location of the stereo pair. This means that the entire panorama of sounds would be audible not merely a center located monophonic reproduction.
When playing back a “true stereo” or Blumlein recording using speakers there will be some crosstalk but no more than would have been in the actual acoustic space. This exclusive separation is only true for binaural stereo…not speaker based reproduction. You can get isolation of left and right by listening to a stereo program on a pair of headphones. I personally don’t particularly like the sound coming from the center of my head. I much prefer to have a pair of stereo speakers reproducing the sound of traditional stereo recording.
The challenge that Dr. Choureiri and others have been dealing with is trying to make binaural recording work outside of headphones, where crosstalk is not a problem, in a pair of loudspeakers. There are plenty of wonderful stereo recordings that present an accurate stereo field without the compromises mentioned in the test above. The real problem with this approach to 3D Audio is that it requires the source recording to be made using a binaural head. And if you think there’s a shortage of real high-resolution audio recordings available, just wait until you try to find binaural recordings at any resolution.