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DVD Audio Too Little, Too Late?
By Jim Taylor
DVD Format Incomplete
When DVD was first introduced, many people were disappointed to learn that the format was incomplete. Only DVD-ROM and DVD-Video were finalized, with variations such as recordable DVD and DVD-Audio left for later definition. The DVD Forum, a multi-industry group dedicated to the development of a single DVD format, wanted DVD-Audio to benefit from the advice of recording industry groups such as the Recording Industry Association of America (RIAA), Europe's International Federation of Phonographic Industries (IFPI) and the Recording Industry Association of Japan (RIAJ). Representatives of these groups formed the International Steering Committee (ISC), which handed a set of recommendations for DVD-Audio to the DVD Forum's Working Group 4 (WG-4). Today, about two years after the debut of DVD and after repeated delays, DVD-Audio is almost ready for prime time. But will anyone care?
Definition Detour
As usual, a slight digression is in order to make sense of the jargon and acronyms. After all, this is a magazine for videophiles, not digital audio engineers.
PCM (pulse-code modulation) audio, specifically LPCM (linear PCM), is the same digital audio format used by audio CDs and LaserDiscs. It's an uncompressed digital representation of an analog waveform. The PCM signal used in audio CDs and Laser-Discs is sampled 96,000 times a second (96kHz), with 16 bits used to store the amplitude of each sample. DVD-Video and DVD-Audio offer variations with more samples and more bits.
In order to save storage space and thus achieve a longer playing time, digital audio signals can be compressed. There are two basic types of compression: lossless and lossy. Lossless compression removes redundant information in such a way that the original data can be completely restored. Lossy compression is based on analysis of human perception, and permanently removes data that is least likely to be noticed. The audio on DVD-Video discs can be uncompressed or lossily compressed. The lossy compression schemes supported by DVD-Video are Dolby® Digital, MPEG-2 audio, and DTS® Digital Surround.* Dolby Digital and MPEG-2 encoding reduce the data by about 93 percent, while DTS reduces it by about 76 percent. DVD-Audio optionally supports the DVD-Video formats and adds Meridian Lossless Packing (MLP). MLP produces about a 50 percent reduction.
What's The Diff?
The existing DVD-Video format already has excellent audio capabilities. In fact, most audio production studios still have not caught up to the level of quality supported by DVD-Video. The rare 24-bit systems in upgraded studios don't often fully achieve the expected level of digital resolution; their analog-digital converters and other components are simply not accurate enough. It took many years before digital audio production equipment was able to fully exploit the 16 bits of resolution provided by CDs (and some would argue that there's still room for improvement). It will likewise take years before production equipment can even get close to the raised bar of 24-bit, 96kHz PCM audio provided by DVD-Video. So it's no surprise that people wonder why anyone needs an even higher sampling rate. Does the reproduction of audio frequencies above 48kHz really benefit anyone other than dogs?** Can today's loudspeaker technology even do justice to the signals?
Other features of DVD-Audio aren't much more compelling than higher sampling frequencies. Lossless compression is nice, providing for longer playing times with no degradation of the original digital signal. Uncompressed (lossless) multichannel audio also seems like an improvement, but tests have shown that most listeners can't tell the difference between an uncompressed PCM signal and a compressed one. In order to enjoy multichannel audio, the listener must be in the sweet spot, surrounded by speakers. But people don't usually sit still when listening to music. Proponents of DVD-Audio are fond of pointing out that an automobile is an ideal environment for surrounding the listener with speakers. However, the noise level in a car makes it impossible to hear the subtle difference between compressed and uncompressed audio. So lossy compressed audio from DVD-Video discs is perfectly adequate. Ironically, the place where multichannel audio quality is most important, the room with the expensive receiver and speakers, is not often used for sitting in one place and listening to audio. A home theatre, of course, adds video that keeps the viewer in one place. But when motion video is added to a DVD-Audio disc, the audio is limited to the formats supported by the DVD-Video spec. This is a very important point: DVD-Audio does not change or improve soundtracks for movies or for any other kind of video on DVD.
Some of the other features of DVD-Audio, such as copyright identification and anti-copy measures, benefit the music industry, not the consumer. The WG-4, in a clever dodge, declined to go beyond the technical parameters of the DVD-Audio format. The independent Copy Protection Technical Working Group (CPTWG) is still evaluating proposals for encryption and for watermarking, a way of embedding extra information into the signal that supposedly doesn't affect the quality but can't easily be stripped out. One bright spot that will come as a welcome surprise to DVD-Video fans, especially in other countries, is that there is no regional coding on DVD-Audio discs.
ony And Philips And SACD, Oh My!
ABack when the WG-4 began accepting proposals for the audio version of DVD, Sony and Philips proposed a system based on their new Direct Stream Digital (DSD) encoding technology. For compatibility with CD players, they recommended discs with both a CD-type data layer and a DVD-type data layer. Their proposal was rejected, ostensibly because the other eight DVD Forum companies were trying to get away from Sony/ Philips-controlled CD technology patents while Sony and Philips were trying to perpetuate them. Sony and Philips, though still members of the DVD Forum, decided to turn their proposal into a competing audio product. Thus was born Super Audio CD (SACD).
The SACD camp claims that single-bit DSD technology is superior to PCM, especially for studio work. But until new DSD receivers appear, the DSD signal must be converted to multichannel PCM before it can be fed to a digital audio receiver. SACDs have the distinct advantage of playing in CD players as well as in new SACD/DVD players. Unfortunately, the physical watermarking used for copy protection on SACDs requires new optical pickup circuitry, so the high-resolution layer won't be readable in the millions of DVD-ROM PCs on the market. And the big disappointment for those interested in video is that SACD adds only text and graphics.
Thanks, But No Thanks
So what's the appeal of DVD-Audio and SACD to the home theatre fan? Not much. The additional technologies mean you must buy new equipment to play the new discs. SACD doesn't include video, and all video on a DVD-Audio disc must conform to the DVD-Video scheme. In other words, the high-quality audio already provided on DVDs is as good as it gets for movies and music video.
In spite of its lackluster benefits, DVD-Audio will succeed, partly because it will ride on the shoulders of DVD-Video and DVD-ROM, and partly because the music industry will promote it in order to gain copy protection features. Within a few years, almost all DVD-Video players will be "universal players," able to play both DVD-Video and DVD-Audio discs.*** DVD-Audio will eventually enter your life, probably when you replace your first DVD player with a new one. But unless you're a fanatical audiophile (you know who you are, with monoblock amplifiers, oxygen-free Teflon speaker cables and sand in your speaker enclosures), the new audio discs just don't give you much to get excited about. They're like cup holders and trip computers in a new car: nice to have, but hardly worth going out and buying a new car for.
* At High Enough bit rates, DTS can achieve lossless compression.
** The Nyquist sampling theorem states that to digitize an analog waveform without aliasing errors in the frequency domain, the sampling rate must be at least twice that of the maximum desired frequency. The average human can hear frequencies up to 20kHz, dictating a sampling rate of at least 40 kHz. Of course, a higher sampling rate is needed to accommodate those with more golfer ears. And some experts argue that subtle overtones and harmonics disappear if very high frequencies are not reproduced.
*** Although it will be a while before universal DVD players appear, producers have the option of creating universal discs from the get go. Any DVD Audio Disc dan be designed to play in all DVD players by adding a Dolby Digital or DTS Digital Surround version of the PCM audio tracks. If this compatibility is important to you, let the music labels know that you demand universal DVD-Audio discs.
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