DVD - Audio versus SACD technology
Technology Wars Episode 5: DVD-Audio vs. SACD

Beta vs. VHS. Pepsi vs. Coca-Cola. Mac vs. PC. Gamecube vs. Xbox. And now DVD-Audio vs. SACD.

The two latest developments in home audio that seem most likely to obtain critical mass with consumers are DVD-Audio and Super Audio Compact Disc (SACD). Each is its own quantum leap from the current CD audio format technology-each offers vastly greater storage capacity and greater quality sound.

The biggest difference between the CD, DVD-Audio, and SACD formats is in how they encode data. Both the DVD format and the CD format accomplish the digital encoding of an analog signal via a process called pulse code modulation (PCM). Essentially, PCM takes a series of digital snapshots of the analog signal wave at various points in the wave’s motion. Your CD player reads the data on a CD, then converts these snapshots back into sound waves by interpolating approximate values for the aspects of the waveform and filling them in between the digital "snapshots" taken by the PCM process, which can then be rendered as music by your amplifier.

The DVD-Video format represented a step format in the quality of the PCM process. The DVDs currently widely available with your favorite movies (except for the original Star Wars trilogy) offer audio quality superior to CD audio. The video data on these discs takes up a large portion of the storage capacity of the disc, though, and therefore the audio portion of the data is compressed, which does not allow for optimum audio quality. DVD-Audio doesn’t have this limitation, so it can offer even higher quality audio, and potential hold an incredible quantity of recorded audio.

DVD-Audio's has a much finer PCM capability than the current CD format. CD offers 16-bit, 44.1 kHz, two-channel data, while DVD-Audio offers 24-bit data, with a sampling rate of 96kHz for six-channel audio, or 129 kHz for two channel stereo. DVD-Audio also offers a storage capacity of up to 7 times as great (approx. 4.7 GB of data) as that of current CD technology. The additional capacity can be used for advanced resolution quality sound, or for longer recordings, plus visual content accessible via your television or PC-liner notes, song lyrics, artist bios, photo galleries, or video clips.

SACD, on the other, features a new technology called Direct Stream Digital (DSD), which is being touted as a “PCM killer” by its backers, Sony and Philips. DSD increases the resolution of music even more than DVD-Audio by closely following the original waveform of the music. By using the DSD process rather than PCM encoding, SACD recordings don't have to subject the original sound waves to the decimation and interpolation stages associated with PCM. DSD records music at a much higher sampling frequency--approximately 2.8224 MHz--and coverts it to 1-bit data. The result is sound that is . . .at least theoretically . . .superior even to DVD-Audio sound. SACD offers up to 6 times the storage capacity of the current CD format.

Now for the bad news. Although many of these new discs include lesser quality audio that will play in a DVD-Video (for DVD-Audio discs) or CD player (SACD discs), each of these new audio formats will require you to purchase a new player in order for you to enjoy the benefits of these new media, and although these players are cheaper than they were when they were first sold, they’re still significantly more expensive than standard CD and DVD-Video players. Many DVD-Audio and SACD players now being manufactured will also play both the DVD-Video and CD formats, though, so you don’t have to add another component to your already cluttered stereo cabinet.

While the difference between ordinary CDs and both new formats is fairly obvious, it’s not clear if the SACD’s DSD technology is really capable of producing sound quality superior to the high quality PCM of DVD-Audio. At current, there are few if any titles available in both formats, so truly scientific evaluation would be difficult. My unprofessional ears we unable to determine a significant difference in sound quality.

It’s still to early to which—if either—of these formats will emerge as the new standard, but either is a step up from what we’re buying today, so, with any luck, regardless of which is left standing after the two formats have slugged it out for a few more years, the CD may soon go the way of the 8-track.

--Matt Parks

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