Article from Dolby Laboratories Inc.
Below: "What is the LFE channel?"
Dolby Digital is an advanced form of digital audio coding that makes it possible to store and transmit high-quality digital sound far more efficiently than was previously possible. First used in movie theaters in 1992, it is the result of decades spent by Dolby Laboratories developing signal-processing systems that exploit the characteristics of human hearing.
2. What program sources deliver Dolby Digital audio?
Dolby Digital audio is available via laser discs, DVD-Video discs, DVD-ROM discs for computers, digital cable systems, direct broadcast satellite (DBS) systems, and digital broadcast TV (DTV). They are usually identified with the Dolby Digital logo.
3. Can I hear Dolby Digital programs over a regular stereo or Dolby Surround Pro Logic system?
Yes, you can use most of the new Dolby Digital program sources with your current playback system, because they incorporate Dolby Digital decoders and provide conventional analog stereo outputs.
However, with many DVD-Video players, digital cable set-top boxes, and other sources, you need a separate multichannel Dolby Digital decoder to experience the thrilling 5.1-channel surround sound used on many Dolby Digital programs.
4. What is "5.1-channel" Dolby Digital?
At the option of their producers, Dolby Digital programs can deliver surround sound with five discrete full-range channels�left, center, right, left surround, and right surround�plus a sixth channel for those powerful low-frequency effects (LFE) that are felt more than heard in movie theaters. As it needs only about one-tenth the bandwidth of the others, the LFE channel is referred to as a ".1" channel (and sometimes erroneously as the "subwoofer" channel). Figure 4-1 illustrates a typical 5.1 playback system; see question 14 on page 4 for further information on speakers, including subwoofers.
5. How does 5.1-channel Dolby Digital differ from Dolby Surround?
5.1-channel Dolby Digital provides two surround channels to Dolby Surround�s one for more precise localization of sounds and a more convincing, realistic ambiance. Also, the surround channels cover the entire audible range (20 Hz � 20,000 Hz), whereas the range of Dolby Surround�s single surround channel is limited (100 Hz � 7,000 Hz). This further heightens realism and gives sound mixers more creative freedom.
In addition, Dolby Digital�s multiple discrete channels enable more sharply-delineated spatial effects, and its ".1" LFE track makes it possible to reproduce low bass effects with stunning impact (twice as loud as the other channels). ...
Read the entire PDF document:
High level description of the Low-Frequency Effects channel (PDF: 17KB)
