Dolby Headphone Overview - TimeForDVD.com

Dolby Headphone™ is a new and powerful digital signal processing (DSP) algorithm that simulates the acoustic soundscape of a 5.1-channel home theater surround sound loudspeaker system through the use of an ordinary pair of stereo headphones. Dolby Headphone potentially works with any multi-channel program source, from Dolby Digital encoded DVD-Video discs, to Dolby Surround Pro-Logic encoded Hi-Fi VHS tapes, to high-resolution multi-channel DVD-Audio discs.

Dolby Headphone allows the listener to enjoy a simulated
5.1-channel home theater system with
an ordinary pair of stereo headphones.
Any pair of stereo headphones will work.

With Dolby Headphone, any multi-channel audio source can be converted into a special 2-channel Dolby Headphone soundtrack. The trick is that the two-channel Dolby Headphone soundtrack contains audio signals that have been manipulated to include sonic spatial cues and ambient information that trick our ears into believing that we're listening to a real multi-channel home theater loudspeaker system. The best analogy is that it's like watching a 3-D movie. The Dolby Headphone soundtrack is analogous to the 3-D encoded image and the special 3-D glasses that trick our eyes into believing that we're seeing a three-dimensional picture.

What Dolby Headphone is not: to be crystal clear, Dolby Headphone is not another noise-canceling technology for headphone listening. (Pun intended.)

The problem with using headphones for an extended period of time is that most listeners suffer from what's called "listener fatigue". Before we explain what that is, let's discuss how listening to loudspeakers works and compare that with listening to headphones.

direct and reflected sounds (diagram courtesy of Dolby Laboratories)

When we listen to a pair of loudspeakers, we hear sounds coming from those loudspeakers and to a lesser extent sounds that are reflected off any side or rear walls. These direct and reflected sounds provide spatial cues to our brains telling us where the loudspeakers are located and how big the room is. With a pair of quality loudspeakers that are set up properly, we can actually hear sounds emanating from a soundstage that is directly in front of us, spread between and sometimes beyond the loudspeakers in the horizontal and vertical planes. This is what audio literature refers to as a three-dimensional soundstage. This ability to precisely image sounds provides a far richer sonic experience than hearing sounds from just the two distinct locations of the loudspeakers. Detailed imaging and the resultant three-dimensional soundstage is one of the key hallmarks of a quality audio system.

5-channel surround sound (diagram courtesy of Dolby Laboratories)

For home theater, the soundstage takes on added dimensionality when a center channel and a pair of surround loudspeakers are added as part of a 5-channel home theater system. With these speakers, movie sound designers can precisely locate any sound in virtually any location in the home theater room. The gives us the illusion of "being there" in the middle of the movie. The point is, when we listen to a system of home theater loudspeakers, we hear the sound coming from various directions: in front of us, from the left, from the right, from either side, or from somewhere in the middle of the room.

When we listen to a pair of headphones, the sounds are fed directly to our ears. What we hear are sounds that come from just outside our left ear, from just outside our right ear, or from outside of both our ears. When the same sound is heard from both ears, it sounds as if it's coming from somewhere inside our head. For most people, this "in-the-head" effect is an unnatural psycho-acoustic effect. After an extended listening session with this unnatural effect, some headphone listeners will experience "listener fatigue". Listener fatigue is a state of mental fatigue caused by the cognitive dissonance that the brain experiences. In other words, our brains know better and get confused since they don't believe the source of the sounds that our ears are hearing.

headphone imaging (diagram courtesy of Dolby Laboratories)

The powerful digital signal processing in Dolby Headphone manipulates the audio signal so that when it is reproduced by a pair of headphones, the imaging sounds as though you're listening to loudspeakers in a room, instead of imaging that's "in-the-head". This more natural "out-of-head" effect not only allows us to fully enjoy a spacious three-dimensional soundstage as intended by the movie sound designer or audio recording engineer, but it allows us to enjoy headphone listening much longer since "listener fatigue" is less likely to be an issue.

The powerful digital signal processing algorithm defined by Dolby Headphone takes any multi-channel audio source (up to 5-channels), processes it to add all sorts of spatial cues and ambient effects through simulated direct and reflected sounds, and outputs a special two-channel audio signal that is reproduced through a pair of conventional headphones.

location cue by differential volume levels and time (diagram courtesy of Dolby Laboratories)

How does Dolby Headphone re-create a sound emanating from one part of the room? Depending on where a particular sound is emanating from, our ears hear the sound at slightly different volume levels and at slightly different times. For example, if the sound comes from the left speaker, then our left ear will hear the sound slightly louder and slightly before our right ear, because the left speaker is slight closer to our left ear than our right ear. This differential effect is how we're able to locate a person that is calling to us from within a crowd. Similarly, each loudspeaker in a 5-channel home theater system has a different acoustic-time signature. By exploiting this phenomenon for each of the five channels, Dolby Headphone is able to re-create the acoustic environment of a 5-channel loudspeaker home theater environment.

What about the ".1" low frequency effects (LFE) channel? The deep bass in the LFE channel is simply folded into the Dolby Headphone soundtrack. Imaging is not as important with low bass frequencies, which are pretty much direction-independent.

For products incorporating Dolby Headphone processing, there are up to three possible simulated environments:

DH1: Reference Room
This setting recreates the acoustic environment of a small, relatively well damped room that is ideal for a home theater. This setting is most appropriate for movies and does well for music listening also.

DH2: Live "Wet" Room
This setting simulates a medium-sized live or "wet" room, which is ideal for music listening.

DH3: Large Room
This setting is designed to simulate the acoustic environment of a large, commercial movie theater.

Not all Dolby Headphone products will provide all three options. Those that only have one setting typically uses the DH1 reference room environment by default. Those that offer multiple Dolby Headphone settings will allow the listener to select among its available choices.

Dolby Headphone can also simulate the acoustic environment of a 2-channel stereo loudspeaker system. Technically speaking, Dolby Headphone stereo mode is simply a subset of the five channel experience in that only the left and right speakers are active. Like the example we discussed above, the Dolby Headphone output re-creates a wide and detailed soundstage that appears in front of the Dolby Headphone listener very much like performers and instruments spread across a stage in a live performance. This works with virtually any 2-channel program source, such as audio CD, tape, MP3-encoded file, and WMA-encoded file (Windows Media Audio).

So what do you need to enjoy or try Dolby Headphone? There are at least two ways:

Editor's Note: If your DVD player does not have a headphone jack, try connecting your DVD player to a TV or A/V receiver with a stereo headphone jack. Just use a pair of RCA stereo audio connectors and connect the left and right stereo audio outputs to your TV or A/V receiver. If you are attempting to use a TV's headphone jack, make sure it does not have any simulated surround sound mode turned on. If you are attempting to use a A/V receiver's headphone jack, make sure any digital signal processing (DSP) modes or simulated soundfield modes are disabled. Any such processing will severely degrade the Dolby Headphone soundtrack.

On June 3, 2003, Artisan Home Entertainment will release T2: Extreme DVD, the second DVD-Video title to feature a pre-encoded Dolby Headphone soundtrack.

As a test of Dolby Headphone, we took the pre-encoded Dolby Headphone soundtrack on the Pearl Harbor DVD for a test spin. From the opening scene of Chapter 1 with the biplane flying over the Tennessee farm field, we were amazed with the realistic "out-of-head" imaging. Skipping to Chapter 3, when Rafe and Danny play chicken with their WWII fighters, we could hear the two aircraft separate into the left surround and right front speakers as they roll right and barely miss each other. Then in Chapter 11, when Rafe engages the Germans in a gruesome dogfight, on-screen and off-screen sounds were pretty well-placed in comparison to our reference 5-channel home theater loudspeaker system. That being a testament to the accurate imaging capability of Dolby Headphone. Starting with Chapter 21, when the Japanese attack began, the flyover and the fly-by sound effects pans of the Japanese Zeros were realistically reproduced by Dolby Headphone.

The true test to any soundstaging and imaging capability is the "closed eyes" test. When our eyes are open and watching the on-screen action, the visual cues help our brains interpret where we're hearing certain sounds. With eyes closed, our brains no longer have the benefit of the visual cues. So we listened to the same segments again with our eyes closed, and were amazed with the accurate three-dimensional soundstage. The imaging from the center channel and surround channels were impeccable. The imaging from the left and right front speakers were less precise, as they sometimes smeared into their same-side surround channel. Most of the time, the imaging from the front left and right channels were pretty good. Readers who don't yet have a real 5.1-channel home theater system will get a flavor of what they've been missing in home theater surround sound. Dolby Headphone is that good.

The bottom line: We were amazed with the Dolby Headphone soundtrack
and give it our emphatic nod of approval.

One limitation of Dolby Headphone is its inability to re-create the surround back channels of Extended Surround sound formats such as THX Surround EX (Dolby Digital EX) or DTS Extended Surround (DTS-ES). Remember that 5.1-channel surround sound formats call for surround sound channel speakers to be placed beside the primary listening location, as shown in the figure above. In the 6.1-channel Extended Surround formats, the additional surround sound speakers (two are usually recommended) are placed behind the primary listening location, for complete 360-degree envelopment. So Dolby Headphone, if it were to ever support these 6.1-channel surround sound formats, would have to re-create sounds coming from behind the listener. The front-to-back imaging is tricky when all you've got to work with are two headphone mini-speakers that are placed side-by-side.

The best way to realize what we mean is to take your Dolby Headphone program and listen to it with your headphones on backwards. Wear them reversed, with the right side earcup/mini-speaker on your left ear and vice versa. With the headphones on backwards, where do you now hear the sounds that originally came from the front? Sure, right-to-left imaging is reversed as can be expected, but forget that for a moment. Try closing your eyes or turning off your TV. What you may notice is that the front-to-back imaging is not so clearly placed anymore. That is, you're probably not as sure whether the sound is coming from in front of you or from behind you. When we're facing the TV screen and our eyes are open, our brains help our ears interpret where sounds should be coming from. Without the visual cues, Dolby Headphone loses some of its ability to image front-to-back. This limitation is easily explained by physics and the classic geometric triangulation problem, and should not be misunderstood as a fundamental deficiency in the Dolby Headphone algorithm. To be fair, Dolby Headphone was never meant to simulate any of the 6.1-channel Extended Surround sound formats, with their back surround channels.

Will Dolby Headphone replace real-world 5.1-channel home theater loudspeaker systems? As good as it is, our opinion is "probably not". Part of the appeal of home theater is sharing the movie experience with your family or friends. If everyone had a pair of headphones on, personal interactions would be difficult. From a pure surround sound performance perspective, Dolby Headphone comes amazingly close to simulating the immersive soundfield of a quality home theater system, though it doesn't quite match the imaging and soundstage of a real system. Additionally, loudspeakers can impart a visceral impact that even the best reference quality headphones cannot possibly deliver. When was the last time you heard your room or furniture rumble while listening to a movie soundtrack on your headphones?

Dolby Headphone is a fairly new technology, having been introduced in 2001. As with most new technologies, it takes a little while for the technology to catch on. But before you know it, you'll be among many who will wonder how they've gotten along without it. We're optimistic that Dolby Headphone will find practical applications in many areas, from portable DVD/CD/MP3/WMA players, to desktop and notebook computers, to in-car and in-flight entertainment systems, to stand-alone DVD players, and to digital TVs. Give it a few years. Then look for the Dolby Headphone logo whenever you shop for an audio/video hardware.

Since we primarily focus on DVD and home theater, we're particularly interested in seeing Dolby Headphone incorporated into A/V receivers. That's the most logical component to incorporate this technology since it serves as the hub of every home audio or home theater system, with all audio sources connected to it.

One of the first A/V receivers to feature Dolby Headphone processing and output is the new Denon AVR-5803, scheduled for market introduction in March 2002. Unfortunately, the price of admission is beyond most "everyday consumers", at a very steep $4,300! We expect many new A/V receivers to include Dolby Headphone in the near future, later in 2002 and certainly more in 2003. At first, only the more expensive models will have Dolby Headphone, like many new technologies at first. But we're confident that Dolby Headphone will eventually find its way into affordable A/V receivers. The intense competition amongst all the A/V receiver manufacturers to provide the most features and maximize "bang-for-the-buck" virtually guarantees that this will be the case. In a couple of years, say by 2004-2005, we expect to see Dolby Headphone processing incorporated into entry-level A/V receivers below $500.

Denon AVR-5803 A/V receiver ($4,300) - one of the first
products to feature Dolby Headphone output

In the portable DVD player and in-car DVD-based entertainment systems market segments, we expect to see Dolby Headphone processing introduced in the next couple of product generations. Dolby Headphone is perfect for the portable audio/video segment. To see what products are available with the Dolby Headphone feature today, visit this Dolby Headphone web page.

Some of you may be asking the question, "should I upgrade to audio/video hardware with the Dolby Headphone feature now?" Only you can answer this question. But consider how you would answer these questions:

In a few years time, Dolby Headphone may be so widespread that this decision becomes a non-issue, especially when it becomes available on hardware at consumer-friendly price points.

Did you find this Dolby Headphone overview helpful? Let us know your thoughts, send an e-mail to us at Feedback@TimeForDVD.com.

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