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DVD-Audio is a digital format for delivering high-fidelity audio content on a DVD. The first discs entered the marketplace in 2000 and, as of 2006, titles are still being released. It is currently in a format war with Super Audio CD, another format for delivering high-fidelity audio content.
Audio specificationsDVD-Audio Whitepaper
DVD-Audio offers many possible configurations of audio channels, ranging from single-channel mono to 7.1-channel surround sound, at various sampling frequencies and sample rates. (The _.1 denotes a Low frequency channel sub woofer for bass.) Compared to the compact disc, the much higher capacity DVD format enables the inclusion of either:
- Considerably more music (with respect to total running time and quantity of songs) or
- Far higher audio quality, reflected by higher linear sampling rates and higher bit-per-sample resolution, and/or additional channels for spatial sound reproduction.
Audio on a DVD-Audio disc can be stored in many different bit-rate/sampling rate/channel combinations:
| 16-, 20- or 24-bit | ||||||
|---|---|---|---|---|---|---|
| 44.1 kHz | 48 kHz | 88.2 kHz | 96 kHz | 176.4 kHz | 192 kHz | |
| Mono (1.0) | ||||||
| Stereo (2.0) | ||||||
| Quad (4.0) | ||||||
| Surround (5.1) | ||||||
Different bit-rate/sampling rate/channel combinations can be used on a single disc as well. For instance, a DVD-Audio disc may contain a 24-bit/96 kHz 5.1-channel audio track as well as a 24-bit/192 kHz stereo audio track. Audio is stored on the disc in LPCM format, which is either uncompressed or losslessly compressed with Meridian Lossless Packing. In uncompressed modes, it is possible to get up to 24/48 in 5.1, and 24/192 in stereo. For 5.1 tracks in either 24/88.2 or 24/96 then MLP encoding is mandatory. If no native stereo audio exists on the disc, the DVD-Audio player may be able to downmix the 5.1-channel audio to two-channel stereo audio if the listener does not have a surround sound setup (provided that the coefficients were set in the stream at authoring). Downmixing can only be done to two-channel stereo, not to other configurations, such as 4.0 quad. DVD-Audio may also feature menus, text subtitles, still images and video, plus in high end authoring systems it is also possible to link directly into a Video_TS folder that might contain Video tracks, as well as PCM stereo and other "bonus" features.
The maximum permissible total bitrate for all streams is 9.6 Megabits per second.
Player compatibility
The introduction of the DVD-Audio format required some kind of backward compatibility with existing DVD-Video players. To address this, most DVD-Audio discs contain, at a minimum, a Dolby Digital 5.1-channel audio track on the discCrutchfield Advisor: SACD & DVD-Audio: Ultra-High-Resolution Music (which can be downmixed to two channels for listeners with no surround sound setup). Some discs also include a native Dolby Digital 2.0 stereo, and even a DTS 5.1-channel, audio track5dot1.com: What is DVD-Audio?.
Some have stated that the cheap optical disc players are most likely to play all formats used by the various burner hardware and software manufacturers.
In addition to a standard single-sided disc, a "hybrid" DVD-Audio disc (HDAD) also exists. One side of the disc contains content that can be played in a standard DVD-Video player (such as the album in Dolby Digital 5.1 audio) and the other side contains content for DVD-Audio players (such as the album in 24-bit 96kHz PCM 5.1-channel audio). An example of a popular album released on an HDAD is The Beach Boys' 1966 album Pet Sounds.
Preamplifier/Surround Processor interface
In order to play DVD-Audio, a preamplifier or surround controller with six analogue inputs was originally requiredTimeForDVD.com: DVD-Audio Tutorial. Whereas DVD-Video audio formats such as Dolby Digital and DTS can be sent via the player's digital output to a receiver for conversion to analogue form and distribution to speakers, DVD-Audio cannot be delivered via unencrypted digital audio link at sample rates higher than 48 kHz (ie ordinary DVD-Video quality) due to concerns about digital copying.
However encrypted digital formats have now been approved by the DVD Forum, the first of which was Meridian Audio's MHR (Meridian High Resolution). The latest incarnation of HDMI (High Definition Multimedia Interface) also allows encrypted digital audio to be carried up to DVD-Audio specification (6 x 24-bit/96kHz channels or 2 x 24-bit/192kHz channels), and future versions will handle additional channels. The six channels of audio information can thus be sent to the amplifier by several different methods:
- The 6 audio channels can be decrypted and extracted in the player and sent to the amplifier along 6 standard analogue cables.
- The 6 audio channels can be decrypted and then re-encrypted into an IEEE-1394 (Firewire) signal and sent to the amplifier, which will then decrypt the digital signal and then extract the 6 channels of Audio. The IEEE-1394 encryption is different to the DVD-A encryption and was designed as a general standard for a high quality digital interface. The amplifier has to be equipped with a valid decryption key or it won't play the disk.
- The third option is via the S/PDIF (or TOSLINK) digital interface. However, because of concerns over unauthorised copying, DVD-A players are required to handle this digital interface in one of the following ways:
- Turn such an interface off completely. This option is preferred by the music publishers.
- Downconvert the audio to a 2 channel 16 bit/48 kHz PCM signal. The music publishers are not enthusiastic about this because it permits the production of a CD quality copy, something they still expect to sell, besides DVD-A.
- Downconvert the audio to 2 channels, but keeping the original sample size and bit rate if the producer sets a flag on the DVD-A disc telling the player to do so.
- Encrypt the digital multichannel signal at the original high sample rate and send it, typically via three S/PDIF digital paths (L/R front, L/R surround, CF/LFE) or HDMI to the processor/preamp for decryption, such that the digital signal is never available 'in the clear' for potential copying.
- A final option is to modify the player, capturing the high resolution digital signals before they are fed to internal D/A converters and convert it to S/PDIF, giving full range digital (but only stereo) sound. There exist already do-it-yourself solutions for some players.
Sound quality
From a purely technical standpoint, the audio resolution of a DVD-Audio disc (sampled at 24-bit and up to 192 kHz) is substantially higher than a standard Compact Disc (which is sampled at 16-bit/44.1 kHz). The original sound recording may have been made at 24-bit, 96kHz (typical for surround) or 24-bit, 192kHz - or even at 64-bit, 384kHz and down-converted for the disc (though this is currently very unusual). However, virtually no hard evidence exists to suggest that people are able to hear a difference between DVD-Audio and CD-Audio. In any case, most consumers do not regard any supposed quality improvements offered as sufficient reason to justify purchasing new playback equipment and repurchasing albums in high-resolution (DVD-Audio or SACD) formats.
Three of the major music labels, Universal Music, EMI and especially Warner Bros. Records, are continuing to release albums on DVD-Audio, but standalone DVD-Audio releases are now rare. Instead, new titles tend to be released as CD/DVD packages (which usually include the album on both CD and DVD-Audio) or DualDisc (which can contain DVD-Audio on the DVD side of the disc). In addition, some titles that were initially released as a standalone DVD-Audio disc, such as The Grateful Dead's "American Beauty" and R.E.M.'s "Automatic for the People", have since been rereleased as a CD/DVD package or as a DualDisc.
See also Comparison of SACD, DVD-Audio, and CD
Copy protection
DVD-Audio discs employ a copy protection mechanism called Content Protection for Prerecorded Media (CPPM)Labriola, Don. August 25, 2003. Digital Content Protection, Part II. ExtremeTech.com. CPPM, managed by the 4C Entity, prevents users from extracting audio to computers and portable media players.
Because DVD-Video's content-scrambling system (CSS) was quickly broken, DVD-Audio's developers sought a better method of blocking unauthorized duplications. They developed CPPM, which uses a media key block (MKB) to authenticate DVD-Audio players. In order to decrypt the audio, players must obtain a media key from the MKB, which also is encrypted. The player must use its own unique key to decrypt the MKB. If a DVD-Audio player's decryption key is compromised, that key can be rendered useless for decrypting future DVD-Audio discs. DVD-Audio discs also can utilize digital watermarking technology developed by the Verance Corporation.
The 4C Entity also developed a similar specification, Content Protection for Recordable Media (CPRM), which is used on Secure Digital cards.
DVD-Audio's copy protection was overcome in 2005Robinson, Stuart M. Robinson. June 7, 2005. DVD-Audio Copy Protection Defeated via WinDVD Software Hack. highfidelityreview.com by tools which allow data to be decrypted or converted to 6 channel .WAV files without going through lossy digital-to-analogue conversion. Previously that conversion had required expensive equipment to retain all 6 channels of audio rather than having it downmixed to stereo. In the digital method, the decryption is done by a commercial software player which has been patched to allow access to the unprotected audio. The method is still in early stages, for example having problems with watermarked disks. As the DVD-A format has not gained wide commercial interest or acceptance, decryption tools are still very primitive.
Such tools are most likely illegal in the United States under the Digital Millennium Copyright Act, and the Recording Industry Association of America has been successful in keeping them off websites. Like much software of dubious legality, they are still distributed from person to person and on the peer to peer networksSlashdot: DVD-Audio's CPPM Circumvented.
References
External links
- All about DVD Part 4: DVD-Audio and SACD at DVDSoftwareGuide.com
- The 4C Entity LLC - licensors of the Content Protection for Prerecorded Media (CPPM) specification
- What DVD-Audio titles are available today?
"DVD-Audio"