For those readers new to the game, DVD-Audio and SACD are audio formats that make use of the high data capacity and bandwidth originally developed for DVD-Video. The two formats are incompatible, using different technologies and making different demands on playback devices. It took a couple of years after their introduction before the first universal disc player was introduced, by Pioneer.

Both DVD-A and SACD avoid the use of lossy compression such as Dolby Digital and DTS, which throws away "redundant data." The new formats promise not only greatly enhanced resolution and dynamic range compared to any other consumer music format, but, in most cases, multichannel sound.

DVD-A and SACD accomplish these goals in very different ways. DVD-A uses Pulse Code Modulation (PCM) digital encoding. CD also uses PCM, but in that format, the digital resolution is limited to 16 bits with a sample frequency of 44.1kHz. DVD-A, thanks to the vastly increased capacity of DVD, can operate in full 5.1-channel mode at digital specs up to 24-bit/ 96kHz, or in 2-channel mode at 24/192. Some multichannel DVD-A discs use less than 24/96 encoding—check those jackets carefully—and 24/192 recordings are comparatively rare. DVD-A is being promoted heavily as a multichannel format, and has even begun finding its way into car audio.

In addition to the high-resolution track, most DVD-A discs include a Dolby Digital (and perhaps DTS) version. This makes them playable in standard DVD players, though the resolution will be limited to that of those data-compressed formats. But DVD-As have no CD track and therefore cannot be played in conventional CD players, either home or mobile.

DVD-A can't carry much video, but most of the recordings do include graphics in some form, though they're largely limited to stills and perhaps a few brief full-motion sequences. Navigating some DVD-A discs can be difficult without turning on your video monitor. This can be a minor nuisance for home theater fans, but it's a major pain in the neck for audiophiles who do not have video displays anywhere near their music systems.

SACD, jointly developed by Sony and Philips, has been promoted and sold from the beginning as an audiophile format. While not a DVD per se, an SACD is designed to have a comparably high data capacity. It employs a digital coding format called Direct Stream Digital (DSD), which samples the music at a rate of 2.8 million times per second. Many SACD recordings are 2-channel, reflecting the format's early promotion to the high-end audio market, but there is now a reasonably good selection of multichannel releases as well. If you're looking only for multichannel recordings, check SACD jackets carefully.

Unlike DVD-Audio recordings, many SACDs carry a conventional CD mix on a separate layer. This makes them appealing to collectors, who can listen to the CD version virtually anywhere. Not all SACD releases use this "hybrid" configuration, but an increasing number do. SACD is also strictly an audio format, carrying no video information whatsoever. There are even dedicated players that play nothing but SACD and CD (no DVD-Video). Some of these, in fact, are 2-channel only—multichannel SACDs need not apply!

Because the primary benefits of SACD and DVD-A are a frequency response well above the audible range and increased dynamic range beyond CD's already formidable level, some listeners have argued that these higher-resolution formats offer no significant audible advantage over CD, apart from their multichannel capabilities. Many audiophiles disagree, definitely hearing an improvement over the sound of CD, which many of them have never been completely comfortable with in the first place.

What audiophiles don't hear, however, is the thunderous sound of a flood of releases in either format. SACD appears to have more titles, but the numbers released in either format, while growing, are still minuscule compared to what you'll find on CD or DVD-V. And before you champion either format as the answer to the prayers of audiophiles everywhere, remember that the technical quality of any recording—not to mention its artistic worth—depends more on the talent in the recording studio than the technology used on the disc.—TJN