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3-D sound real or a gimmick?

Audio — 17 May 2011

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3-D sound real or a gimmick?

So what is 3-dimensional sound? Is it real and can it be achieved with stereo speakers?

With well-placed speakers and some clever engineering tricks, it’s possible to create a “surround sound” audio experience that mimics real life. In fact, most high-end systems have something close to that as a goal; to recreate the sound actually recorded at the original event.

In fact, most people involved with high-end audio are familiar with the idea of soundstage – which is the ability of the stereo system to create a palpable 3-dimensional image behind the loudspeakers. This image can be enhanced by turning off the lights in the listening room or closing ones eyes. Properly done, the acoustic image is divorced from the loudspeakers and freely floats in space giving one the illusion of being at the event itself.

An even simpler example is the center channel of any stereo system. That center channel is, of course, an illusion created by equal sound coming from the left and right loudspeakers and reaching your ears at the same moment in time.

But it’s not surround sound

One of the drawbacks of stereo 2-channel audio attempting to reproduce a 3-dimensional image is the requirement that the listener be in a perfectly positioned location in order to get the full benefit of that sound field. A good example of this is Q Sound, an older technique used to produce true surround sound from 2-channel recordings. A great example of this is Roger Water’s Amused to Death CD. If you get your head positioned perfectly in the center, you can appreciate sound enveloping the listener.

Most surround sound is typically produced via multiple speakers and associated with home theaters, rather than high-end audio systems. However, there has been some development in bringing 3-D sound from 2-channel sources.

A bit of history

The story starts with stereo itself.  Years ago there was only mono.  As the story goes, Alan Blumlein (a British engineer) and his wife were attending one of the new “talkie” movies that had been recently introduced (before World War II).  Sitting in the sudience he noticed an actor walk across the screen (from left to right) but his voice didn’t follow the actor (mono).  He turned to his wife and said “I can fix that”.  His idea was to make an acoustic version of a stereo viewer (you may remember the old stereo 3-D viewers of the day).  It’s really a similar principal and he patented the idea.  For years, stereo has dominated the audio industry until the advent of multi-channel audio (Quadraphonic) which fizzled out in the 1970′s as a primary audio experience and resurfaced later as surround sound focused primarily on home theater.

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The first attempts at bringing surround sound to two channel systems were popularized by processes like Q Sonics, Ambisonics, Polk Audio’s SRS speaker system and Bob Carver’s famous Sonic Holography. These systems all relied on the idea that if the system could prevent the left ear from hearing what only the right ear should be hearing (and vice/versa) the sound would be much closer to what happens in real life. In real life all sound comes from only a single point source. To understand, picture a guitar playing, or a singer singing. The sound comes from a single source. In a two-channel system, there are two sources of sound (the left and right loudspeakers) that are attempting to recreate a single source. This is easily detected by the human hearing system and rejected as “unnatural”.

Using phase cancelation techniques, it is possible to cancel the sound of one speaker while playing from the other and thus fooling the ear into believing there is really only one source of sound. The problem with all these systems is the same problem the basic two-channel audio system has: the sweet spot requirement. To appreciate the cancellation technique employed in pseudo surround systems, the listener must either be wearing headphones or positioned perfectly between the loudspeakers. Listeners off-axis do not appreciate the effects.

Recent innovations

Recent innovations include the Yamaha soundbar, the Bose 3-D television and the Bang an Olufsen $85,000 television set. These innovations are quite complicated but appreciate a wider sweet spot. Recently, there has been even more work released.

Princeton University professor Edgar Choueiri has announced a new system that, while not addressing the sweetspot problem, does address a tonal balance problem common to many of these systems..

“With surround sound you get a feeling of sound around you, but you can’t fool someone into thinking that a person has walked up to you to whisper into your right ear, or that a fly is flying around your ear,” said Choueiri, a mechanical and aerospace engineer.

Choueiri says he’s developed a true 3-D audio system that could revolutionize your next movie experience because it is much truer to life.

People who have experienced a demonstration “had a very positive reaction, almost shocked,” Choueiri said. “People are used to stereo or surround sound and suddenly they hear a person going around their head with a scissors giving them a haircut. They have visceral reaction.”

The challenge

3-D sound does more than merely surround you: It enables your brain to paint a three dimensional image of an event. For example, when listening to a symphony orchestra via just two loudspeakers, you’ll be able to hear the bass playing on one side of the concert hall, the violin on the other, just as you would in the concert hall itself. In real life, though, the sound of the both the violin and bass would combine and reach your left and right ears at different times. Your brain analyzes these impulses near instantaneously and determines exactly where the sound must be coming from.

3Daudio 51211 02 3 D sound real or a gimmick?

So, to record for 3-D audio via two loudspeakers all you need is two microphones, Choueiri said. If the microphones are placed inside the ears of a dummy head, the microphones will record the correct 3-D queues needed for humans to hear in 3-D.

Sound too simple? Indeed. The trick in producing 3-D audio lies not in the recording, but in the playback.

If you play these recorded queues back in two regular loudspeakers, your right ear will hear the queues intended both for right and left ears, as will your left ear. This phenomena is called interaural crosstalk.

“These queues get corrupted when your left ear hears the right speaker and your right ear hears the left speaker,” Choueiri said. “This is called crosstalk. And without cancelling the crosstalk the queues get mixed up and your brain won’t get the information it needs to hear in 3-D.”

The solution

Choueiri used well known phase cancellation filtering techniques to reduce the interaural crosstalk, but what’s unique is his results. The real tricky part — and this is where Choueiri and his team at Princeton’s 3D3A Laboratory came in: The filter had to maintain a sound’s integrity.

“Previously any attempt to do crosstalk cancellation resulted in strongly coloring the sound to the point where you would not accept it as tonally correct,” said Choueiri. “Any listener would just realize that’s not a piano anymore. That sounds like something else. Our contribution was crosstalk cancellation without coloring the sound. That’s what makes this technology commercially feasible and acceptable to the human ear.”

In other words, the piano still sounds like a piano.

3-D sound will enter the commercial market within a few months, Choueiri said. He declined to give details, but suggested that a company that now has a product on the market without 3-D audio will bring out the next generation of that same product with 3-D audio.

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PSTracks Staff

PSTracks staff utilizes the great talents of the staff at PS Audio, including engineering, programming, customer service, sales, marketing and our executives. This is a team of dedicated customer-centric people at our Boulder Colorado facility who care about the connected world, music and the high-end. If you are ever in Boulder Colorado, we would encourage you to stop by and visit. We have two beautiful listening rooms and we give out impromptu tours whenever someone drops by to say hello.

(3) Readers Comments

  1. Soundminded

    February 26, 2012 at 7:25 am

    The technique of binaural recording and playback (as differentiated from stereophonic recording although both are 2 channel systems) has been widely known since at least the 1960s, possibly the 1950s, maybe even earlier. The original idea was to place the microphones inside a dummy head, the dummy sitting where a listener in a concert hall would be, and the playback was through headphones. That would put the same sounds that would have reached you were you there instead right at your ears where they would have been. At least that was the theory. It doesn’t work. When you listen to such an arrangement the sound appears to be coming from inside your head. The problem stems from the fact that when you turn your head the sound turns with it. Your brain comes to the only conclusion possible and very quickly. It appears to be inherent in the way the brain processes sound.

    Multiple proposals and attempts have been made to somehow adapt binaural recordings to loudspeaker playback. One idea was “nearphones” which placed multiple small speakers near your head presumably with multiple binaural recordings made at different angles at the same time. Another used accelerometers to accomplish the same thing by switching or panning recorded tracks fed to headphones when you move your head. The latest high tech incarnations take a different approach, they try to produce something between headphones and speakers. About 4 years ago I became aware of “Ambiophonic” sound invented by Ralph Glassgal. Originally he placed a wall between two closely spaced speakers he calls ambiopoles. This wall extended from the speakers to your seat and you put your head against the wall such that each ear would hear only one speaker just the way the 19th century stereoscopic viewers put an image of a bird on one side of a board and a cage on the other. Each eye saw only one image. When held at the right distance your brain would put the bird inside the cage, at least it seemed that way. Glassgal and Choueiri both devised electronic processors that perform cross speaker phase cancellation. The right channel signal is delayed, phase inverted, and its amplitude adjusted, then fed to the left speaker so that it arrives 180 degrees out of phase at the left ear at the same time the undelayed sound from the right speaker arrives at the left ear, hence they cancel (they also add at the right ear but that inconvenient fact may have at first been ignored. Perhaps Choueiri’s new filter compensates for that too.) The same is done with the signal and speaker to the opposite channel. This is intended to accomplish the same result as the wall but without the objectionable physical wall in the room. As frequency gets higher and wavelengths shorter, the location in space where this cancellation effect occurs satisfactorily becomes more limited. I think the practical effect may be limited to below 4khz and limiting the FR in the processing circuit may be the source of the tonality problem due to additions below 4khz to the uncancelled ear.

    You can experience Glassgal’s result on his website, just Google Ambiophonic (not Ambiosonic) sound. There are some sample processed tracks and instructions on how to use them.

    Glassgal takes his concept several steps further. These include placing additional left and right speakers with delays at 55 degrees to the listener where he says IACC (interaural cross correlation) is at a minimum and a system of surround speakers using additional processing to create longer delays. He’s also added two more ambiopoles directly behind the listener. I visited Ralph last summer at his Ambiophonic Institute, actually his home in Rockleigh NJ. He was most hospitable and spent considerable time demonstrating his very elaborate and clearly very expensive system designed for this purpose. What I heard was about what I’d heard from his web site. To me, when positioned very carefully with respect to the speakers I hear sound floating somewhere in a plane between me and the speakers over a very wide angle, at least 150 degrees horizontally. But that’s all I hear. On Choueiri’s web site I hear the voices in the video-teleconference demonstration at approximately the locations the participants appear to be sitting but that is all. I did not hear the bee buzzing around my head, just moving left and right.

    So far while both of these similar ideas are interesting, faking out the human hearing mechanism to create an unexpected audible illusion, I’m not convinced either of them has the potential to live up to its claim of being able to create concert hall sound. Both strike me as having practical problems as well. Both rely on preventing destructive interference from room reflections at different phase relationships arriving at the listener which would partially or totally negate the desired effect. Both are optimized for binaural recordings but there is an existing library of many millions of stereophonic recordings which cannot be fully adapted to the system. Both rely on placing your head in one fixed spot to work which means that only one person at a time can experience its effects (something I find objectionable in many high end audio systems as well.)

    All of these systems including not just adaptations of binaural recordings but multichannel and other systems have several things in common. They all recognize the inadequacy of the two channel stereophonic paradigm to live up to the promise of accurate reproduction of live music. They all use novel methods that are not compatible with existing recordings. It is not clear existing recordings can be adapted to take advantage of them. And so far I haven’t heard one of them that performs the way it’s claimed to by its inventors. But at least they are trying something different. That’s a step in the right direction as I see it.

    • February 26, 2012 at 8:33 am

      Great article, thank you for taking the time to write it.

      Interaural crosstalk and its elimination through phase cancelation at the opposing ear has been around for years and has taken many different forms – this fellow only using the technique to some different advantage. The first time I ever heard it was when Polk Audio put it in their SDA loudspeaker system many, many years ago.

      Today’s versions still have your head in a vise problem and have interesting effects, sometimes startling.

      I have been working for a few years on a different but similar process that does not have a sweet spot and can be appreciated anywhere in the room and from a single enclosure, not a stereo or multi-speaker approach. While still a prototype, those that have heard it seem to appreciate it.

      • Soundminded

        February 27, 2012 at 5:41 am

        I have been experimenting with an entirely different idea for a very long time. Mine has no sweet spot either. I think anyone who builds anything himself or invents anything novel no matter how simple or elaborate is proud of his brainchild. In this industry hyperbole has been used up, the English language has been exhausted advertising them a long time ago. Only by direct experience can anyone make any reasoned judgments about the value of any new ideas. The opportunities for such experiences seems to me to have become increasingly limited as the industry declines especially at the retail level. Trade shows hardly give much opportunity to demonstrate new ideas to potential customers except at their most superficial esposure. Unless new ideas can be developed by a small business they are likely to go nowhere. Large industry seems to have lost interest in this sector as well. I guess they don’t hold out much hope for potential profits in the mid and long term anymore. Given this industry’s recent history who can blame them?

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