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DVD-Audio Tutorial

High resolution stereo and multi-channel music

article last updated on 6.5.2002 | printer-friendly format click for printer-friendly format   

DVD-Audio logo 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

Meridian Lossless Packing (MLP) logoTo 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).

Aaron Neville's "Devotion" available on DVD-Audio 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?

Super Audio Compact Disc (SACD) logoWhat 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.

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In This Article


> It's a DVD!

> Pulse Code Modulation (PCM)

> High Resolution Stereo (2-Channel) Audio

> Multi-Channel Audio

> Lossless Data Compression

> Extra Materials

> Backwards Compatibility with DVD-Video players

> Availability of DVD-Audio Albums

> Other Equipment

> What About the Super Audio Compact Disc (SACD) Format?

> Should You Buy Into the DVD-Audio Format Now?


Also Read:


> DVD Overview

> DVD Tutorial

> DVD-Video Tutorial

> Super Audio CD Overview


DVD & Blu-ray Release Dates


> August 2010

> September 2010

> October 2010

> November 2010

> December 2010

> January 2011

more >>   


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