Frequently asked QUESTIONS about DOLBY DIGITAL

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6 L C R and right speakers, add 1 ms of delay for each foot it is closer. For example, if dimension C in Figure 11-b is one foot less than L or R, set the time delay to 1 ms. If your seating area is wide, with several viewers in a row as in a movie theatre, it’s best to place the left, right, and center speakers all in line, as shown in Figure 11-c, and use no center time delay. Finally, if it is necessary to place the center speaker further back than the left and right speakers (not illustrated), select a –1 ms delay (for a one foot difference) or –2 ms delay (for two feet), if these options are provided. If they are not provided, use “0” delay. 22. What is the “Midnight Mode” on my new Dolby Digital A/V receiver? Dolby Digital soundtracks can have a very wide dynamic range between soft and loud sounds. At a full playback level, this can be thrilling, providing a truly theatrical experience, particularly for movies. Late at night, however, the loud sound effects found on some movie soundtracks could disturb your family or neighbors. But if you turn down the volume to “keep the peace,” the dialogue will be hard to hear, and subtle low-level effects may get lost altogether. What you’d really like to do is turn down the volume on just the loud effects, turn up the volume on quiet sounds, and keep the dialogue at the same level. This is exactly what Dolby Digital’s Dynamic Range Control feature does. To help explain its function, manufacturers of Dolby Digital L C R L C R L = C = R: L = R > C, small seating area: L = R > C, wide seating area: Center delay = 0. Center delay (ms) = L or R – C (ft.). Center delay = 0. Figure 11-a. Figure 11-b. Figure 11-c. Figure 11: Setting center channel time delay. decoders have come up with names like “Midnight Mode” for this feature (see Figure 12). Figure 12: With Dynamic Range Control on, the full dynamic range (A) of the program is reduced (B), as predermined by the producers. The amount of compression is not arbitrary, but is decided in advance by the soundtrack’s producers, and coded right onto the soundtrack. Some Dolby Digital decoders let you select various amounts of the available compression (e.g., 50%, 75%, 100%), while others provide only 100% when the compression mode is selected. 23. I’m tired of having to adjust the volume every time the program changes or I switch sources or TV channels. Can Dolby Digital help? Yes. Conventional program sources often force you to readjust the volume when you change channels or play a different video. With Dolby Digital program sources, on the other hand, a feature called Dialogue Normalization lets you set playback volume and forget it. Dialogue Normalization automatically adjusts the volume when you change Dolby Digital programs so that the level of the dialogue remains constant. It does not alter the dynamic range, only the overall playback level, based on data <strong>about</strong> the average soundtrack loudness that is coded into the program signal (see Figures 13 and 14). Figure 13: The average level of conventional program sources, and even individual programs, varies greatly. Figure 14: Dolby Digital’s Dialog Normalization maintains a consistent playback level for all programs keyed to their dialogue level. With Dialog Normalization, you can “channel surf” when watching digital TV without having to adjust the volume each time you change channels. And you can play an evening’s worth of DVD-Video discs without ever touching the volume control. 24. What equipment do I need to play Dolby Digital laser discs? Dolby Digital laser disc players do not have a built-in Dolby Digital decoder; they output the Dolby Digital data stream from laser discs on a radio-frequency (RF) carrier that requires demodulation prior to Dolby Digital decoding. If you wish to play the Dolby Digital soundtrack on laser discs, therefore, be sure that the disc player has a “Dolby AC-3 RF” output, and that your Dolby Digital decoder unit includes an RF demodulator specifically for laser disc use. Not all decoder units provide the demodulator, because no other Dolby Digital program source, including DVD, requires it. If you have an older laser disc player and don’t want to decode the Dolby Digital tracks
on newer discs, they will play perfectly well on your older player. On laser discs, the Dolby Digital track is encoded on what used to be the right FM analog track, leaving the standard PCM digital stereo tracks intact for conventional stereo and Dolby Surround Pro Logic playback. The left FM analog track may contain a mono version of the soundtrack, commentary, or other material (see Figure 15). One final note: laser discs with 5.1-channel Dolby Digital soundtracks were originally identified as Dolby Surround AC-3, “AC-3” being the technical term for the digital audio Figure 15: Soundtrack configurations of conventional laser discs (top) and those with Dolby Digital audio (bottom). coding upon which Dolby Digital is based. Today the simpler term “Dolby Digital” is used instead to identify laser discs, like other formats, that have Dolby Digital soundtracks. 25. What equipment do I need to receive satellite broadcasts with 5.1channel Dolby Digital sound? To receive the 5.1-channel soundtrack on broadcasts such as Dolby Digital-encoded theatrical films, you’ll need a satellite receiver that provides a Dolby Digital output (the generic “Digital” output on conventional satellite receivers does not handle Dolby Digital signals). As with other Dolby Digital components, you connect the receiver’s Dolby Digital coaxial or optical output to a digital input on your Dolby Digital decoder unit. Standard stereo audio, usually Dolby Surround-encoded, is broadcast simultaneously, so you need a new satellite receiver only if you wish to receive the Dolby Digital soundtrack. 26. How can I receive high-definition (HD) satellite TV transmissions with Dolby Digital sound? To receive high-definition programming transmitted via satellite, you will need an HD satellite receiver, and possibly a new, larger dish. Most receivers are equipped like most DVD- Video players, that is, with a built-in, two-channel Dolby Digital decoder with analog stereo outputs, and a Dolby Digital output for 5.1-channel sound with an external 5.1-channel Dolby Digital decoder unit. 27. Can my Dolby Digital home theater system decode the new digital TV broadcasts? Yes, it will. Whether highdefinition (HD) or standarddefinition (SD), all digital television (DTV) broadcasts in the U.S., Canada, and other countries that have adopted the ATSC television standard (www.atsc.org) are transmitted with Dolby Digital. Dolby Digital audio is also an option for broadcasts in areas such as Europe using the DVB digital TV standard. All such broadcasts are compatible with existing Dolby Digital decoders. Like other Dolby Digital program material, the audio format of DTV broadcasts varies from mono to full 5.1-channel surround sound. Because most TV facilities have to gear up for multichannel audio production and distribution, many DTV programs are being broadcast initially in two-channel Dolby Digital (often Dolby Surroundencoded for four-channel playback with Dolby Surround Pro Logic decoding). DTV sets and tuners also vary with respect to the number of audio channels they provide. Some have built-in two-channel Dolby Digital decoders, while others have 5.1-channel Dolby Digital decoders for connection to a Dolby Digital-ready A/V receiver (see question 12). Others include not only Dolby Digital decoding but also amplifiers and speakers. Most DTV receivers have a separate digital output that provides the undecoded Dolby Digital signal for connection to your A/V receiver or other unit with 5.1-channel Dolby Digital decoding. As a result, you can add a DTV receiver to your Dolby Digital home theater system at any time, without fear of obsolescence or costly equipment duplication. 28. How can I receive digital cable programs with Dolby Digital sound? Digital cable television systems can provide you with another source of programming for Dolby Digital playback. The number of channels with Dolby Digital cable transmissions varies as with DTV broadcasts and other Dolby Digital program sources. All digital cable set-top boxes incorporate a two-channel Dolby Digital decoder with stereo analog outputs for compatibility with conventional stereo and home theater systems, while some units also provide a digital output for multichannel playback via an A/V receiver or other unit with a 5.1-channel Dolby Digital decoder. 29. Can I purchase DVD- Video discs with Dolby Digital soundtracks in Europe? Yes, Dolby Digital audio is used on DVD-Video discs throughout the world (see question 9). A word of caution, though: while the audio and video technical standards are the same for DVD-Video worldwide, discs purchased in one part of the world may not play at all in another part of the world due to “regional coding.” 7
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Frequently asked QUESTIONS about DOLBY DIGITAL

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