A Multichannel Music Primer
Multichannel music is moving into the mainstream, with many musicians and studios exploring the possibilities of the medium in their recordings. Studios are also beginning to reissue older recordings, "remixed" to multichannel formats. The audio advantages of multichannel surround recordings are many. If you're listening to a "live" performance, a multichannel recording will put you in the middle of the audience. In-studio recordings can capture the acoustical ambiance of the studio or concert hall in which they are recorded, or put you right in the middle of the band itself. Let's examine some of the different formats that are available now for multichannel music, as well as some that are on the horizon.

• DVD-Audio.

  DVD-Audio has improved on PCM audio technology used in CDs by taking advantage of higher sampling rates — up to 192 kHz, compared to 44.1 kHz for standard CDs. Plus, DVD-Audio discs use the Meridian Lossless Packing (MLP) system that allows discs to hold up to seven times as much information as standard PCM CDs. The result is richer, more detailed sound.

  More importantly, for our discussion, nearly all DVD-Audio discs are engineered for surround sound with up to six discrete channels of high-definition audio. Most DVD-Audio discs also contain a compressed Dolby® Digital version of the music for backwards compatibility with standard DVD players. DVD-Audio discs typically contain added video and graphics content, although DVD-Audio is primarily a hi-fidelity audio format. As of early 2004, several manufacturers have DVD-Audio car receivers in development or ready for market, including models from Kenwood, Rockford Fosgate, Panasonic, and Alpine.

• Super Audio CDs (SACDs).

  Sony and Philips, the companies that teamed up to create the original audio CD, have reunited to develop Super Audio CD technology. SACD uses a new process of sound recording and reproduction called Direct Stream Digital™ (DSD). DSD enables a much more direct signal path than the Pulse Code Modulation (PCM) format of original CD, which requires a number of interpolation and over-sampling filters during recording and playback. The result of DSD's simplified signal path, and of its ultra-high 2.82 MHz sampling rate, is a more faithful reproduction of the original source material and richer, warmer sound.

  Although SACDs look the same as standard discs, they can hold much more digital information than regular CDs. All SACDs contain a studio-mixed, high-resolution stereo signal, and many also contain a high-resolution surround sound signal, which can carry up to six independent channels.

  Many (but not all) SACD recordings are hybrid discs. They contain two distinct layers of musical information — a Super Audio layer and a standard PCM CD layer. These hybrid discs deliver high-resolution sound when played on SACD players, and they're backwards compatible for standard digital sound with regular CD players. While SACD holds a lot of promise as a high-resolution multichannel format, no manufacturers are, as of yet, producing SACD equipment for the car.

• Dolby® Digital 5.1.

  We usually think of Dolby® Digital 5.1 when we think of multichannel DVD movie soundtracks. The good news for audio enthusiasts is that most DVD-Audio discs also contain a Dolby® Digital 5.1 version of the music for backwards compatibility with standard DVD players. Dolby® Digital 5.1 uses a compression scheme (or codec) to hold the information on the disc, so there is a slight drop-off in quality between DVD-Audio playback and Dolby® Digital 5.1. However, there are numerous DVD receivers available for the car that have Dolby® Digital 5.1 decoding or can be connected to outboard 5.1 surround sound processors. If you're putting together a mobile video system or want to get on board now with multichannel music, purchasing a DVD receiver makes a lot of sense. Remember, if you decide to upgrade your system to DVD-Audio later, the DVD-Audio discs you've bought for your system will sound even better.

• DTS.

  Like Dolby® Digital, DTS® provides 5.1 channels of digital audio. However, DTS® uses less compression than Dolby® Digital. As a result, some say that the sound produced by DTS® is slightly more accurate than the sound produced by Dolby® Digital. A limited number of music discs are available with DTS® 5.1 soundtracks. To use them, your receiver or processor must have DTS® decoding capabilities.

• Dolby® Pro-Logic IIreg;.

  Dolby® Pro-Logic II® processes a stereo (2-channel) recording to create multichannel information, giving any two-channel recording (like a regular audio CD) a more spacious and enveloping feel. Receivers with built-in Dolby® Pro-Logic II® capabilities are available, or will be available soon, from Blaupunkt, Clarion, JVC, Kenwood, and Rockford Fosgate.

• HD Radio technology and satellite radio.

  The ability to receive a digital signal on your car receiver holds great potential for the future of car audio, and there is engineering work being done that will allow digital broadcasts to carry multi-channel music. XM Satellite Radio and Neural Audio unveiled SEE (Spatial Environment Engine) at the 2004 CES show in Las Vegas. This digital signal processing technology allows 2-channel broadcasts with special "watermark" information to reproduce a convincing 5.1 channel surround sound experience when used in conjunction with a decoder. XM hopes to introduce this technology at the consumer level sometime soon. Over-the-air digital radio services may benefit from similar technology, as iBiquity Digital, the developer of HD Radio technology, and SRS Labs are collaborating to develop multi-channel broadcast technology.