FAQ: Home Cinema AudioFormat

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Dolby Digital & Dolby Surround Pro Logic & Pro Logic II

1. What is Dolby Digital technology?

Dolby® Digital technology 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, Dolby Digital technology is the result of decades spent by Dolby Laboratories developing signal-processing systems that exploit the characteristics of human hearing.

2. What programs deliver Dolby Digital audio?

Dolby Digital can be enjoyed via DVDs, DVD recordable and playback discs for computers, laser discs, digital cable systems, direct broadcast satellite (DBS) and direct-to-home (DTH) systems, and digital broadcast television (DTV/DVB). Sources are usually identified with the Dolby Digital logo.

3. What is 5.1-channel Dolby Digital?

Dolby Digital programs can deliver surround sound with up to five discrete full-range channels: Left, Center, Right, Left Surround, Right Surround-plus a sixth channel for powerful low-frequency effects. 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).

4. How does 5.1-channel Dolby Digital differ from Dolby Surround?

The technology behind 5.1-channel Dolby Digital provides two surround channels, instead of the one from Dolby Surround, for more precise localization of sounds and a more convincing, realistic ambience. Also, Dolby Digital's 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). The increased range of Dolby Digital 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 the ".1" LFE track makes it possible to reproduce low bass effects with stunning impact (twice as loud as the other channels).

5. Does 5.1-channel Dolby Digital make Dolby Surround obsolete?

No. Dolby Surround will continue to be a preferred method for delivering surround encoded content within the space of a stereo signal. This is why all Dolby Digital decoder units also incorporate a digitally implemented Dolby Surround Pro Logic® decoder.

Programs encoded in Dolby Surround can be played back in mono, stereo, or with a Dolby Surround Pro Logic decoder that recovers the four original channels. These programs can also be played in Dolby Pro Logic II for five independent full-range channels.

6. Can I hear 5.1-channel Dolby Digital programs over a regular stereo, Dolby Pro Logic, or Dolby Pro Logic II system?

Yes. All Dolby Digital decoders, whether 5.1-channel or two-channel, have a unique feature called "downmixing" that assures full compatibility with any playback system. At your choice, the decoder will create "on the fly" from 5.1-channel programs a two-channel mix encoded in Dolby Surround for playback over a home theater system with Dolby Pro Logic decoding; a two-channel stereo mix for regular stereo and headphone playback; a mono mix for playback over a mono TV set; and even five independent full-range channels through a Dolby Pro Logic II system. A system equipped with Dolby Pro Logic II can decode five full-range channels from the two-channel Dolby Digital downmix source.

Thus, producers of 5.1-channel programs need only provide the one 5.1-channel mix. The decoder in the playback system does the rest, automatically making the signal conform to the particular playback circumstances.

7. Do all Dolby Digital programs provide 5.1 channels?

No. Dolby Digital soundtracks can provide anything from mono to full 5.1-channel surround sound. DVDs of movies can even carry multiple versions of the soundtrack that differ in number of channels. A disc might contain a 5.1-channel sound mix with the dialogue in one language, a two-channel mix encoded in Dolby Surround in another language, and a mono track with the director's comments or other supplementary information. The default soundtrack will vary from disc to disc, so always check the DVD's language menu for the choices offered.

8. Do all DVDs have Dolby Digital soundtracks?

Discs in countries such as the US that use the NTSC broadcast TV standard must provide at least one soundtrack in either of two formats: Dolby Digital or PCM (the format used on CDs). In countries using the PAL TV standard, including much of Europe, the discs must include at least one soundtrack in any one of three formats: Dolby Digital, PCM, or MPEG. Due to these requirements and the options they permit, not all discs may have Dolby Digital soundtracks.

Dolby Digital, however, is the only universal multichannel standard, and every DVD player sold worldwide incorporates Dolby Digital decoding. The vast majority of discs, therefore, do include at least one soundtrack in Dolby Digital.

9. How can I determine the soundtrack's format?

The Dolby Digital logo on a DVD or other program source indicates that it has one or more soundtracks encoded in Dolby Digital, but it does not indicate the number of channels. To help identify the number of channels, Dolby Laboratories is encouraging the use of the channel format symbols on program packaging.

In addition, to prevent confusion at playback, data identifying the original production format of a program's soundtrack is incorporated right into the Dolby Digital signal. Some Dolby Digital decoder units use this data to display the soundtrack type on the display panel.

10. Do all program sources with Dolby Digital decoding provide 5.1-channel sound?

As with Dolby Digital program material, "Dolby Digital" on a component such as a DVD player indicates that it incorporates Dolby Digital decoding, but not the number of channels.

Many program sources, including all DVD players and digital cable set-top boxes, provide a built-in, two-channel Dolby Digital decoder with analog stereo outputs. For 5.1-channel playback, most units have a separate digital output for connection to an external unit, such as an A/V receiver, that has its own 5.1-channel Dolby Digital decoder.

Some DVD players do provide a built-in Dolby Digital 5.1-channel decoder with multiple analog outputs that can be connected directly to a "Dolby Digital-ready" receiver, as described in question 11, for 5.1-channel sound. However, you will not be able to use the internal Dolby Digital decoder for other program sources, and these players don't offer the full range of options provided by external Dolby Digital decoder units. On the other hand, they are an inexpensive way to upgrade to 5.1-channel Dolby Digital initially, and provide a digital output so that you can later bypass the built-in decoder and use an external one.

11. How do I convert my current Dolby Surround Pro Logic system to 5.1-channel playback?

If your current system consists of separate audio components, you will need a 5.1-channel Dolby Digital processor.

If you have a newer "Dolby Digital-ready" A/V receiver with analog multichannel connectors for an external Dolby Digital decoder, you can add a decoder anytime, using the receiver's built-in Dolby Surround Pro Logic decoder in the meantime for satisfying home theater sound. You can also connect the multichannel outputs of a DVD-Video player that has built-in 5.1-channel Dolby Digital decoding to this kind of receiver. An external decoder is still needed, however, for other Dolby Digital program sources (see question 10).

Note: Be sure that the new decoder unit has a sufficient number of digital inputs to accommodate all the Dolby Digital program sources you expect to use (for example, DVD-Video player, digital cable set-top box, digital TV receiver). Also, if you plan to play Dolby Digital laser discs, be sure that the unit also includes the necessary RF demodulator (only laser discs require this feature).

12. If I convert to a 5.1-channel system, will I still be able to play Dolby Surround program material?

Yes, all Dolby Digital decoders are compatible with Dolby Surround Pro Logic technologies, so you can continue to enjoy Dolby Surround programs after converting your system.

13. Can I use my current speakers after I convert my system?

Yes, you can use your current speakers, because the configuration for Dolby Digital's five main channels is essentially the same as that for Dolby Surround.

14. What kind of speakers should I get for an all-new Dolby Digita system?

The ideal Dolby Digital playback system uses identical full-range speakers for the Left, Center, Right, and each Surround channel. If you do not have identical speakers, be sure that the overall tonal characteristic, or timbre, of all the speakers is similar. This is equally important for both Dolby Pro Logic and Dolby Digital playback.

Most speaker manufacturers offer timbre-matched home theater speakers. Many also offer systems combining matched compact speakers for the five main channels with one or more separate subwoofers for the non-directional bass; such a "satellite" system can prove an effective, space-saving solution.

15. My DVD player has two digital outputs, one optical and one coaxial, and my Dolby Digital decoder has both kinds of inputs. Which should I use?

Under most conditions, optical and coaxial digital connections work equally well. Under some rare circumstances, however, coaxial cables, particularly very long ones, can pick up radio frequency (RF) interference generated by household appliances or nearby high-tension power lines or broadcast towers.

If you hear RF interference, you can try relocating the cables, moving your components closer together, or changing to optical cables.

Note: Some DVD players and Dolby Digital decoders have either a coaxial or an optical connector. Be sure that the units you purchase both use the same type.

16. Why does my Dolby Digital decoder provide time delays?

The delay ensures that the viewer hears sound from the surround and front speakers simultaneously, as the surround speakers in a home theater system are usually closer to viewers than the front speakers. For Dolby Surround Pro Logic, which has less inherent channel separation than Dolby Digital, a slightly longer (by 15 milliseconds) delay ensures that sound from the surrounds arrives just after sound from the front. This delay reduces the audibility of sound leakage from the front to the surround speakers.

Some Dolby Digital decoder units also provide an adjustable Center-channel delay to ensure that the viewer hears sound from all three front speakers simultaneously.

17. How do I set the surround time delays?

The time delays in your Dolby Digital decoder are preset to provide good results in most home theater installations. If you wish to fine-tune the adjustments, consult the decoder's instruction manual.

Most units allow you to adjust the surround delay in either the Dolby Digital or Dolby Pro Logic mode. Because the relationship between the two delays is fixed, you only need to set the delay in one mode. The decoder will automatically provide the appropriate delay whenever you switch to the other mode.

To establish the proper surround delays for your system, you need to know the distances between your viewing position and a front speaker and a surround speaker. Then, using Dolby Pro Logic mode or Dolby Digital mode, find the distance to the surround speaker on the graph's vertical axis, and the distance to the front speaker on the horizontal axis. Lines drawn from these points will intersect on the graph at the recommended delay setting.

18. How do I set the Center channel time delay?

You do not need a center delay (that is, the delay can be set at 0) if your seating area is small, and with the three front speakers positioned equidistant from the viewers. If the Center speaker in such a small area must be placed more in line with the Left and Right speakers, thereby bringing it closer to the viewers than the Left and Right speakers, add 1 ms of delay for each foot it is closer.

If your seating area is wide, with several viewers in a row as in a movie theater, it is best to place the Left, Right, and Center speakers all in line and use no center time delay.

If it is necessary to place the Center speaker further back than the left and right speakers, select -1 ms (for a one foot difference) delay or -2 ms (two feet) delay, if these options are provided. If they are not provided, set the delay at 0.

19. What is the "Midnight mode" on my new Dolby Digital A/V receiver?

Midnight mode allows low-volume listening with high-volume benefits, reducing the volume on just the loud effects of a program, increasing the volume on quiet sounds, and maintaining dialogue at a consistent level. A Dolby Digital feature applies dynamic range compression that preserves low-level sounds, prevents dramatic passages from getting too loud, and keeps dialogue intelligible during lower-level listening.

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 (for example, 50, 75, 100 percent), while others provide only 100 percent when the compression mode is selected.

20. 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, 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 about the dialogue that is coded into the program signal.

With dialogue normalization, you can "channel surf" when watching digital TV without having to adjust the volume each time you change channels. Those extra-loud commercials will be tamed. And you can play an evening's worth of DVD-Video discs without ever touching the volume control.

21. What equipment do I need to receive satellite broadcasts with 5.1-channel Dolby Digital sound?

You need a new satellite receiver that provides a Dolby Digital output (the "digital" output on conventional satellite receivers does not pass Dolby Digital signals). As with other Dolby Digital components, you connect the Dolby Digital coaxial or optical output to a digital input on your Dolby Digital decoder unit.

Standard stereo audio, usually encoded in Dolby Surround, is broadcast simultaneously, so you need a new satellite receiver only if you wish to receive the Dolby Digital soundtrack.

22. 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 dish. Most satellite receivers are equipped like most DVD-Video players: 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.

23. Can I use my Dolby Digital home theater system for the new digital TV broadcasts?

Yes, you can. Whether high-definition (HD) or standard-definition (SD), all digital television (DTV) broadcasts use Dolby Digital audio in the US, Canada, and other countries that have adopted the ATSC television standard (www.atsc.org). Dolby Digital audio is also used in some countries like Australia in conjunction with other transmission standards, and is an optional multichannel audio delivery format in DVB and DTH broadcasts in Great Britain and Europe.

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 (or sometimes encoded in Dolby Surround for four-channel playback with Dolby Surround Pro Logic decoding). Movies prepared with 5.1-channel Dolby Digital soundtracks for theatrical release are the primary source of multichannel Dolby Digital DTV programming.

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 may have 5.1-channel Dolby Digital decoders for connection to a Dolby Digital-ready A/V receiver (see question 11).

Most DTV receivers have a separate coaxial or optical digital output for connection to your A/V receiver or other unit with 5.1-channel Dolby Digital decoding. You can add a DTV receiver to your Dolby Digital home theater system at any time, without fear of obsolescence or costly equipment duplication.

24. 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 varies, but all digital cable set-top boxes in the US incorporate a two-channel Dolby Digital decoder with stereo analog outputs for compatibility with conventional stereo and home theater systems, and fully equipped units also provide a digital output for connection to your A/V receiver or other unit for 5.1-channel playback with an external multichannel Dolby Digital decoder.

25. Can I purchase DVDs with Dolby Digital soundtracks in Europe?

Yes, Dolby Digital audio is used on DVDs throughout the world (see question 8). 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, or TV format (such as PAL or NTSC). Check the packaging to find out if the disc has any regional limitations or if it is recorded in a TV format that is incompatible with your system.

26. I'm thinking about getting a PC with a DVD-ROM drive. Will it give me 5.1-channel Dolby Digital sound?

That depends on the computer's configuration and its DVD/audio card, so check the specifications carefully to be sure you get the audio capability you want.

Most PCs can be connected to external playback equipment ranging from amplified stereo speakers to a full 5.1-channel playback system. The latter includes not only full home theater systems, but compact, multichannel PC speaker systems incorporating amplifiers and Dolby Digital and/or Dolby Surround Pro Logic decoding. PCs bundled with stereo amplifiers and speakers may have a built-in two-channel Dolby Digital decoder for the DVD-ROM player that will downmix 5.1-channel soundtracks.

PC audio outputs may include analog power amplifier outputs, line level outputs for external amplifiers, headphone jacks, and RF carriers. They may also provide conventional PCM digital audio outputs, and/or outputs that provide the undecoded Dolby Digital data stream via S/PDIF (IEC 61937), USB, IEEE 1394, LAN, wireless link, or other format connections.



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Απάντηση: FAQ: Home Cinema AudioFormat

Dolby Pro Logic IIx

1. What is Dolby® Pro Logic® IIx?

Dolby Pro Logic IIx is an extension of Dolby Pro Logic II technology. This highly sophisticated algorithm processes native stereo- and 5.1-channel material to produce 6.1 or 7.1 output channels.

Dolby Pro Logic IIx expands choice in playback system configuration (allowing 5.1, 6.1, or 7.1 playback channels) and, when incorporated into an audio/video (AV) receiver or processor, allows a convenient upgrade path from a traditional 5.1-channel sound system to 7.1 output channels.

2. Does Dolby Pro Logic IIx replace Dolby Pro Logic II?

No. Dolby Pro Logic IIx uses the same core technology as Dolby Pro Logic II, but extends its functionality. Dolby Pro Logic II technology will continue as the primary surround decoder for two to 5.1-channel material. Pro Logic IIx will be integrated by manufacturers into hardware components that offer 6.1 or 7.1 output capability.

3. Why does Dolby Pro Logic IIx sound more natural than competing formats?

For a few reasons. One is the newly developed approach in steering logic design, which provides unprecedented smoothness and precise dynamics. Another is the lack of signal coloration achieved by employing the simplest audio path, with as little filtering of the audio as possible.

4. What were the sonic goals in developing Dolby Pro Logic IIx?

* Improved surround envelopment
* Enhanced sense of spatial depth
* Improved directionality
* Larger listening area, commonly referred to as the "sweet spot"
* Compatibility of all native stereo and 5.1-channel content with 6.1 and 7.1 playback configurations

5. What are the key differences between Dolby Pro Logic IIx and other existing 6.1- and 7.1-channel offerings?

* Dolby Pro Logic IIx is the only technology package that covers both 6.1 and 7.1 speaker configurations.
* Dolby Pro Logic IIx maintains the sonic clarity of Dolby Pro Logic II across all sources and output modes, ensuring unmatched aesthetic consistency and purity.

Dolby Pro Logic IIx introduces no artificial coloration during playback. It remains true to the artist�s intent.

6. Are the Surround and Back channels full range?

Yes, with a 20 Hz to 20 kHz frequency response.

7. Will manufacturers offer Dolby Pro Logic IIx in a 7.1 satellite/sub configuration?

Yes. With proper bass management executed within the receiver, a 7.1 satellite/subwoofer configuration�where all low frequencies are routed to the subwoofer�is indeed possible.

8. Will Dolby Pro Logic IIx process DTS 5.1 content, and is it compatible with DTS-ES discrete and matrix-encoded software?

Processing of DTS content is an available option. While Dolby Pro Logic IIx technology is fully compatible with DTS and DTS-ES, whether a product supports them is, of course, dependent upon DSP capability and hardware design.

9. Will Dolby Pro Logic IIx process multichannel DVD-Audio or SACD content to 7.1-channel playback?

Yes, it will process both technologies. That is one purpose of the Music mode. It is important to note that in order for this to occur, your A/V receiver or processor must be able to perform digital signal processing of the external input signal (on IEEE1394, six analog line-level inputs, or some other proprietary connection) from a DVD-Audio player. A receiver that simply passes the six analog channels through and applies some preamplification gain to the signals will be incapable of processing a 5.1 source into a 7.1-channel output.

10. Does Dolby Pro Logic IIx introduce any sound delay?

There is some surround delay in certain modes, as in all other Dolby Pro Logic decoder systems. Otherwise, no.

11. Is any front-channel information being mixed into the Rear speakers by Dolby Pro Logic IIx?


12. What happens in signal processing behind the Center Width control?

When a logic decoder �steers� the Center signal, it is, in essence, removing Center channel signals from the Left and Right outputs. The Center Width control allows the amount of steering that is applied to Center signals to be modified. It reduces the "hard Center channel" that sometimes results from Center steering of stereo encoded soundtracks.

13. Is the Panorama mode more, or less, useful in a 7.1 environment?

The function of the Panorama mode is to create a more enveloping front surround field. It is equally useful when applied to Dolby Pro Logic IIx processing.

14. What are the differences between Music mode and Movie mode?

Surround programs are primarily mixed like movies. When shows are mixed in surround, they are monitored through the surround decoder that will be used for playback in the cinema or home. Movie mode is the reference decoder mode for any such surround-encoded program.

Music mode brings the benefits of a highly natural and balanced multichannel surround soundfield to content that was not specifically encoded for surround playback.

15. Why is there a Game mode on what is generally regarded as a traditional home theater device?

Video games represent a significant and expanding percentage of home theater use. In fact, more than 30 percent of gamers are connected to a home theater system. Also, video games today are extremely sophisticated, with high-resolution video performance and dramatic 5.1 surround audio tracks. The ideal gaming experience, of course, is on a large-screen television connected to a high-power audio system.

16. What specific signal processing is occurring during Game mode?

The Game mode was implemented to ensure that the bass impact from pure surround effects is delivered to the subwoofer, fully optimizing the visceral impact of panned rear effects.

17. Is there a height element to Dolby Pro Logic IIx?

No, because content is not being made with specifically encoded height information. Without encoded content, any effect created, however pleasurable, would be mere speculation.

18. What is the effect of the Surround and Back speakers?

The Surround and Back speakers enable a more enveloping, more involving, and more precise listening experience.

19. Are the Surrounds and Backs stereo channels?

Yes, but they are not discrete. The Surround and Back channels are each derived from Dolby Pro Logic IIx logic decoding, so the separation varies in response to the input signal.

20. Does Dolby have a preference for Rear and Back Surround speaker configurations?

Not necessarily, since different rooms often benefit from different solutions. However, direct radiators often provide maximum clarity and detail and, therefore are often recommended.

21. Will you develop Dolby Pro Logic IIx matrix encoders for the entertainment industry?

Possibly. But it is worth noting that unlike Dolby Pro Logic II, which requires its own encoders to achieve maximum benefit, Dolby Pro Logic IIx can be fully exploited using today�s encoding tools and mixing consoles.

22. What components are necessary to upgrade from Dolby Digital EX/Dolby Pro Logic II to Dolby Pro Logic IIx?

Aside from an A/V processor equipped with the new Dolby Pro Logic IIx algorithm, you would need an additional amplifier and an additional speaker matched to the existing back speaker for full integration of Dolby Pro Logic IIx.

Most A/V receivers equipped with Dolby Pro Logic IIx, on the other hand, will include the additional amplifier necessary to upgrade from 6.1 Dolby Digital EX to 7.1-channel Dolby Pro Logic IIx.


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