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article last updated on
5.29.2003 | printer-friendly
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What is Dolby Headphone?
 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.)
What are the benefits of Dolby Headphone?
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.
 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.
 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.
 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.
How
does Dolby Headphone work?
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.
 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. Up
to three simulated environments
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 in stereo mode
 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). What
do you need to use Dolby Headphone?
So what do you need to enjoy or try Dolby
Headphone? There are at least two ways:
-
Dolby Headphone decoder: The most
typical way to enjoy Dolby Headphone technology is to buy it as part
of an A/V receiver, DVD-Video or DVD-Audio player, desktop or laptop
PC, MP3 player, game console, portable stereo, or conventional and
digital TV. In terms of software for your desktop or laptop
computer, you can use Sonic's CinePlayer
1.5 Surround DVD player, which provides a Dolby Headphone
soundtrack through the headphone jack. Though the possibilities of hardware incorporating Dolby Headphone is almost limitless, few products
today actually offer Dolby Headphone processing. Visit this Dolby
Headphone web page to see what other products are available
with the Dolby Headphone feature.
-
Dolby Headphone
pre-encoded soundtrack:
The most readily available way to enjoy Dolby Headphone is a DVD-Video
title that includes a Dolby Headphone pre-encoded soundtrack.
Just plug in your favorite pair of headphones into the headphone
jack of your DVD player or A/V receiver and select the Dolby
Headphone soundtrack from the DVD menu and you're all
set. Any set of headphones will do, but as with most things in audio, better quality
or reference quality headphones will provide a richer sonic
experience. Beyond that, no special hardware or decoder
required because Dolby Headphone processing was already applied and the resulting signals are
pre-encoded as a special
Dolby Headphone soundtrack.
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.
Pearl Harbor DVD: an example of a
pre-encoded Dolby Headphone soundtrack
 The first DVD-Video title to feature
a
pre-encoded Dolby Headphone soundtrack is Pearl
Harbor, first released to DVD on December 4, 2001. (Click here to read our full
review of the Pearl Harbor: 60th Anniversary Commemorative Edition
DVD. Pearl Harbor is available in three
versions. Read about them here.)
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.
So how does Dolby
Headphone sound? 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.
Does Dolby Headphone
have any limitations? 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
ever replace surround sound loudspeakers?
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? What
audio/video components are available with Dolby Headphone?
 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. Should
you upgrade to audio/video hardware with Dolby Headphones?
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:
-
How often will you use headphones for
listening?
-
Do you suffer from "listener
fatigue"?
-
How much of a premium are you willing to pay
for a product that has Dolby Headphone vs. one that you would
buy if Dolby Headphone was not a consideration?
-
How long can you put off your purchase?
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.
Additional Info:
What do you want to do next?
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you find this Dolby Headphone overview helpful? Let us know your
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Note: All logos and diagrams relating to Dolby Headphones on this web page are courtesy of
Dolby Laboratories and/or Lake
Technologies.
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