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article last updated on 6.5.2002
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You may have heard of DVD-Audio (sometimes referred to as just
"DVD-A") while shopping for a new DVD player.
So what's the deal with DVD-Audio? What is so
good about the DVD-Audio format? How is it better than the
popular audio CD
format? Is it something worth looking into? What do you need in order to enjoy DVD-Audio
to its fullest potential? For answers these
questions and more, keep reading...
It's a DVD! The first the thing you need to know is
that DVD-Audio is part of DVD specification (you probably guessed that
already). The DVD specification dictates the physical aspects
and data capacities of the DVD format, as described in our DVD
Tutorial. Be sure to read that first, if you haven't done so
already. As you have
guessed, DVD-Audio is the audio application format of the
general DVD specification. DVD-Audio includes:
We will go into more detail about each of these
DVD-Audio unique features. Pulse
Code Modulation (PCM) There are a number of ways
to represent an analog audio signal as a digital signal. Think
of the analog audio signal as a continuously variable voltage that
fluctuates in frequency and
amplitude to represent the frequency of the sound and the loudness of
the sound, respectively. By far the most common method of digitizing
an analog signal (i.e., representing the analog audio signal as a
stream of digital 1's and 0's) is Pulse
Code Modulation (PCM). PCM is the same digital technology as
used by the audio CD format. PCM works by sampling an
analog signal at regular intervals and encoding the amplitude value of
the analog signal in a digital word using. The analog
signal is then represented by a stream of digital words. Without
trying to get too technical, you might be interested in knowing that
digital sampling theory (the Nyquist criterion, to be exact) says that
in order to reproduce an analog signal with a certain frequency, you
must sample at least twice as fast as that frequency.
Given that we humans can hear sounds with frequencies from 20 Hz
to 20,000 Hz, we need to sample at least at 40,000 Hz (or 40,000 times
per second) in order reproduce frequencies up to 20 kHz. That's
why the CD format has a sampling frequency of 44.1 kHz (or 44,100
times per second), which is slightly better than twice the highest
frequency that we can hear. Note, we emphasized the phrase
"at least". While sampling frequencies twice that what
we can hear is a minimum requirement, it can be argued (mathematically
even) that twice is not fast enough to accurately capture the
characteristic of these high frequency signals. That's why in
PCM, higher sampling frequencies offer better accuracy in reproducing
high frequency audio information. The CD format's 44.1 kHz
sampling frequency is barely adequate for reproducing the higher
frequencies in the range of human hearing. The other
part of PCM is word length. Each sample, or snapshot, of
the analog signal is characterized by its magnitude. The
magnitude is represented by the voltage value in the analog signal and
is represented in the digital signal as a data word. A data word
is a series of bits. A bit is binary digit that has a value of
"1" or "0". The longer the data word, the
wider the range of analog voltages that can be represented as well as
finer gradations of values in that range. In other words, the
longer the word length, the wider the dynamic range (i.e., the
difference between the softest sounds and the loudest sounds) and the
finer the nuances of sounds can be recorded. The CD format has a
word length of 16 bits, which is enough to reproduce sounds with about
96 dB (decibels) in dynamic range. Is the 44.1 kHz
sampling rate and 16-bit word of the audio CD format adequate?
While audiophiles and discerning audio enthusiasts would definitely
say "no", we would guess that most "everyday
consumers" would initially think "yes".
Those who are into high fidelity music reproduction say that the audio
CD sounds cold and exhibits occasional "ringing" effects in
the upper most frequencies when compared to high quality analog
recordings on the LP and studio master analog tapes. Many of
these enthusiasts are right, and some of their claims can proven
mathematically and empirically. That is why the consumer
electronics manufacturers have designed the DVD-Audio format. We
would hazard to guess that once the "everyday consumer"
hears the new DVD-Audio format on a properly calibrated, good quality
audio system, they would be able to readily hear the differences and
the improvement over the CD format. High
Resolution Stereo
(2-Channel) Audio
One of the novelties of DVD-Audio is that it
offers much higher resolution Pulse Code Modulation (PCM).
DVD-Audio supports sampling rates of up to 192 kHz (i.e.,
the audio signal is sampled 192,000 times per
second, or more than quadruple (4 times) the sampling rate of audio CD)
and up to 24-bit word length. As we explained above, the higher
sampling rate means more accurate and realistic reproduction of the higher
frequencies. Is the 192 kHz sampling rate enough? At over
nine times the highest frequency of human hearing, you would think
so. But only careful listening tests of a high quality and
well-balanced system will tell.
Though DVD-Audio supports up to 192 kHz sampling,
not all audio program material has to be recorded using the highest
rate. Other sampling rates are supported: 44.1 kHz, 48 kHz, 88.2
kHz, and 96 kHz. For two-channel stereo mode, high resolution
audio usually means a sampling rate of 192 kHz. The
word length is increased up to 24 bits, meaning that a theoretical
dynamic range of 144 dB can be achieved. We say theoretical
because it is not currently possible to achieve such high dynamic
ranges yet, even in the best of high-end components. The
limiting factor is the noise level inherent in the electronics, due to
thermal noise and other factors. The best signal-to-noise ratio
that can be achieved in today's state-of-the-art components is about
120 dB. So it does seem that the 24-bit word length should be
more than enough for the foreseeable future. Thought DVD-Audio
can actually support word lengths of 16-bit and 20-bit, high
resolution stereo usually means a word length of 24-bit.
Multi-Channel Audio
Another novelty of the DVD-Audio format is its
capability for multi-channel discrete
audio reproduction. That is up to six, full-range,
independent audio channels can be recorded. Once you hear your
favorite artists and albums recorded in the multi-channel format, you
too may be convinced that it's wonderful experience and may realize
that there's some missing in stereo recording when you switch
back. There is real strong compelling reasons for multi-channel
music. Among them, it allows us to hear not just the music, but experience
the performance as though it's live in our own living room. No
stereo music program, no matter how wonderfully recorded, can approach
this feeling.
Usually, the sixth
channel is used as the low
frequency effects (LFE) channel, just like in a 5.1-channel
home theater system, to drive the subwoofer. But the sixth
channel is actually full frequency and can be used as a center
surround channel (placed behind the listener, as in a home theater EX
system) or as an overhead channel (placed well above the listener)
for added height dimensionality to the soundstage. The
application and placement of the six audio channels in a multi-channel
DVD-Audio format is only limited by the imagination of the recording
artist and the recording/mixing engineer. Note that
multi-channel DVD-Audio does not always mean 6 channels or 5.1
channels Sometimes it is just 4 channels (left front, right
front, left surround, and right surround) or 3 channels (left front,
center, right front). And in terms of sampling rates and data
words, multi-channel DVD-Audio can use up to 192 kHz and up to 24-bit word length.
But practically speaking, multi-channel DVD-Audio usually uses 96 kHz
sampling, because of data capacity limitation of the DVD-Audio disc.
Remember, 6-channel audio uses three times the data capacity of
two-channel stereo when both use the same sampling rate and word
length. Speaking of data capacity, DVD-Audio uses a form of data compression
in order to fit the high resolution stereo and/or multi-channel
digital information. Lossless Data Compression  To store the massive
quantity of digital audio
information efficiently, the DVD Forum has approved the use of Meridian's proprietary
lossless
(i.e., no digital information is lost
in the encoding and decoding process) encoding/decoding algorithm as
part of the DVD-Audio format. It is appropriately named Meridian
Lossless Packing (MLP) algorithm.
Editor's Note: It should be noted
that some sources erroneously report that DVD-Audio disc does not use
compression for its high-resolution stereo or
multi-channel audio. Such sources are simply wrong. The DVD Forum has chosen Meridian's proprietary
lossless encoding/decoding algorithm. Lossless means that no digital information is lost in the encoding and
decoding processes, and that the original digital bitstream is
re-created bit-for-bit coming out of the decoder. The algorithm is
appropriately named Meridian Lossless Packing (MLP). Such sources are confusing
lossy compression with compression as a
whole. There are two types of compression: lossy
(where data is lost at the compression stage, like MPEG-2,
Dolby Digital,
and DTS) and lossless
(where the data is preserved bit-for-bit through the compression and
decoding processes). It is a fact that the DVD-Audio format still compresses the
digital audio information on the disc, however, the compression format
is lossless. It's analogous
to the use of Winzip or PKZip to compress data files on your personal
computer. When you unzip the zip file on the receiving end, the original file is re-created
bit-for-bit.
Extra Materials
The DVD-Audio application format supports table of contents, lyrics, liner notes,
and still pictures. Additionally, many (if not all) DVD-Audio
titles are actually combination DVD-Audio and DVD-Video disc (or
DVD-Audio/Video for short). As you can guess, record labels can
use the DVD-Video portion of the DVD to include artist interviews,
music videos, and other bonus video programming. Similarly,
DVD-Audio discs may actually include DVD-ROM content, which can be
used for interactivity on a DVD-ROM drive equipped computer. The
possibilities are nearly endless.
Backwards Compatibility with DVD-Video Players In
order to hear the high-resolution stereo (2-channel) or multi-channel
PCM program on the DVD-Audio disc, you will need a DVD-Audio player.
However, in order to
provide some level of backwards compatibility with existing (DVD-Video
only) DVD players, many (if not all) DVD-Audio titles are actually
combination DVD-Audio and DVD-Video disc (or "DVD-Audio/Video"
disc for
short). In the DVD-Video portion on
DVD-Audio/Video discs is a multi-channel soundtrack
using Dolby Digital
and/or optionally DTS
surround sound which can be played back by existing DVD-Video players. The DVD-Video players look for the
DVD-Video portion of the disc and plays the Dolby Digital or DTS
soundtracks. Sure, the Dolby Digital and DTS soundtracks uses
lossy compression and do not feature the high-resolution stereo and
multi-channel information, but you'll be pleased with how good music sounds
in these DVD-Video audio formats, particularly DTS. So when
you're ready to invest in DVD-Audio albums, make it a point to look
for this DVD-Video compatibility feature (look for the
"DVD-Audio/Video" label).
Availability of DVD-Audio Albums
To date, not many titles have been released to DVD-Audio.
In fact, there's only a handful of DVD-Audio titles released since the
format's launch in the summer of 2000. The first label to
release DVD-Audio titles was Silverline / 5.1 Entertainment.
Recently, Warner Records has entered the DVD-Audio market with some
releases.
Other Equipment
We just noted above that to hear the high resolution
stereo (2-channel) or multi-channel PCM programs on the DVD-Audio
discs, you will need a DVD-Audio compatible DVD player.
Additionally, you'll need an A/V receiver that features 5.1-channel
analog inputs and an "analog direct" mode. The
5.1-channel (or 6-channel) analog inputs are required to connect a
DVD-Audio player. Due to copyright concerns, no digital audio
outputs are allowed for DVD-Audio's high-resolution PCM audio
signal, only the 6-channel analog outputs are allowed. The A/V
receiver's "analog direct" mode is strongly recommended so
that the receiver bypasses its normal digital signal processing (DSP)
circuits that usually degrade the high-resolution DVD-Audio signal,
due to the additional analog-to-digital and digital-to-analog
conversion stages. To connect the DVD-Audio player with the
receiver, you will need six sets of interconnects (RCA type) for the
six channels of analog audio. If you plan to listen
to DVD-Audio seriously, ideally you will want to consider five
identical, full-range speakers. But practically, it's difficult
to have a floor-standing center channel speaker if your audio system
also serves as a home theater (since a home theater usually requires a
horizontally-oriented center channel speaker). Another practical
constraint is the additional cost of using four identical speakers for
left/right front and left/right surround channels. So
practically speaking, the same 5.1-channel speaker set-up that you
have for home theater could be used for DVD-Audio playback. Just
make sure that the DVD-Audio player has an adequate bass management
feature that allows you to route the bass frequencies to those
speakers that can handle it. And understand that these
compromises make it less than ideal for the full-fledged DVD-Audio
experience.
If you're planning to listen to DVD-Audio/Video
albums with just your DVD-Video player, then it's like playing back
any DVD-Video title. Your existing DVD-Video player, A/V
receiver, and 5.1-channel surround sound speaker system will do the
job. No additional equipment is necessary.
What About the Super Audio Compact Disc (SACD) Format?
 What about the other high-resolution audio format,
Super Audio Compact Disc (SACD)? SACD poses an interesting and
compelling alternative to the DVD-Audio format. Like DVD-Audio,
SACDs support high-resolution stereo (2-channel) and multi-channel (up
to 6 discrete, full range channels) audio. But unlike DVD-Audio,
it does not use PCM. Instead, SACD technology is based on what's
called Digital Stream Direct (DSD), which is fundamentally different
from PCM and proponents of DSD claim that it is far superior to PCM
technology.
Additionally, hybrid SACDs feature a CD
layer which is completely backwards compatible with the 700 million CD
players worldwide. In other words, the hybrid SACDs look like an
ordinary audio CD to existing CD players. This means you can
listen to hybrid SACDs in your car's CD player, using your current CD
changer in your home audio system, in your Sony WalkMan CD player, or
on your boom box. You can't do this with DVD-Audio albums.
But not all SACD discs are of the hybrid type, however. On the
other hand, SACDs cannot contain video content as do DVD-Audio/Video
discs. Nevertheless, the SACD format poses as a strong contender
for the new high resolution audio format. To learn more about
the SACD format, read our
Super Audio CD Overview.
Should You Buy Into the DVD-Audio Format Now?
With competition (if you want to call it that) from
the SACD camp, does it make sense for you to buy into the DVD-Audio
format now? Well, that's a tough question, and only you can
answer. Everyone's desires, budget, and expectations are
different, so it's hard to generalize. However, you should be
aware that affordable "universal" players promising SACD,
DVD-Audio, DVD-Video, CD, CD-R, and CD-RW compatibility are coming in
late 2001. If you're planning to buy your first DVD player or
upgrade your current DVD-Video player, it may be worth your while
looking into such "universal" players, especially if you
think you're ready to make your venture into the world of
high-resolution stereo and multi-channel music. If you think
you're ready, we'll be back soon with information on these new
"universal" players. Sign
up for our free e-Newsletter,
and we'll keep you informed.
What do you want to do next?
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