DVD-Audio
| File:DVD-Audio Logo Black.png | |
| Media type | Optical disc |
|---|---|
| Encoding | Meridian Lossless Packing or uncompressed LPCM |
| Capacity | up to 8.5 GB |
| Read mechanism | 640 nm wavelength semiconductor laser |
| Developed by | DVD Forum |
| Usage | Audio storage |
| Extended from | DVD |
DVD-Audio (commonly abbreviated as DVD-A) is a digital format for delivering very high-fidelity audio content on a DVD. DVD-Audio is not intended to be a video delivery format and should not be confused with video DVDs containing concerts and music videos. The first discs entered the marketplace in 2000. Future occasional DVD-Audio releases are expected and/or have been announced. DVD-Audio was in a format war with Super Audio CD (SACD), another format for delivering high-fidelity audio content. Neither has gained a strong position in the marketplace. As media players that can play both DVD-Audio and SACD (and many other formats) are available, both are likely to co-exist.
Audio specifications
DVD-Audio offers many possible configurations of audio channels, ranging from single-channel mono to 5.1-channel surround sound, at various sampling frequencies and sample rates.[1] (The ".1" denotes a Low-frequency effects channel (LFE) for bass and/or special audio effects.)
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) | Yes | Yes | Yes | Yes | Yes | Yes |
| Stereo (2.0) | Yes | Yes | Yes | Yes | Yes | Yes |
| Stereo (2.1) | Yes | Yes | Yes | Yes | No | No |
| Stereo + mono surround (3.0 or 3.1) | Yes | Yes | Yes | Yes | No | No |
| Quad (4.0 or 4.1) | Yes | Yes | Yes | Yes | No | No |
| 3-stereo (3.0 or 3.1) | Yes | Yes | Yes | Yes | No | No |
| 3-stereo + mono surround (4.0 or 4.1) | Yes | Yes | Yes | Yes | No | No |
| Full surround (5.0 or 5.1) | Yes | Yes | Yes | Yes | No | No |
| Optical discs |
|---|
 |
Different bit-rate/sampling rate/channel combinations can be used on a single disc. For instance, a DVD-Audio disc may contain a 96 kHz/24-bit 5.1-channel audio track as well as a 192 kHz/24-bit stereo audio track. Also, the channels of a track can be split into two groups stored at different resolutions. For example, the front speakers could be 96/24, while the surrounds are 48/20.
Audio is stored on the disc in Linear PCM format, which is either uncompressed or losslessly compressed with Meridian Lossless Packing. The maximum permissible total bitrate is 9.6 Megabits per second. Channel/resolution combinations that would exceed this need to be compressed. In uncompressed modes, it is possible to get up to 96/16 or 48/24 in 5.1, and 192/24 in stereo. To store 5.1 tracks in 88.2/20, 88.2/24, 96/20 or 96/24 MLP encoding is mandatory.
The LFE channel is actually full range, and can be recorded at the same resolution as the other channels. This permits it to be used instead as an extra main channel, for example as a "height" speaker above the listening position; this has been done on some releases. Such usage is non-standard, and will often require special set-up by the end user.
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..
Player compatibility
With the introduction of the DVD-Audio format, some kind of backward compatibility with existing DVD-Video players was desired, although not required. To address this, most DVD-Audio discs also contain DVD-Video compatible data that allows the standard DVD-Video Dolby Digital 5.1-channel audio track on the disc[2] (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 96/24 5.1-channel, audio track.[3]
Because the DVD-Audio format is a member of the DVD family, a single disc can have multiple layers and even two sides that contain media. A common configuration includes a "DVD-Video" zone on a DVD-Audio formatted single sided disc. The high-resolution, multichannel audio losslessly encoded using MLP is only playable on DVD-Audio hardware but the DVD-Video zone, which can contain Dolby or DTS 5.1 mixes and even video makes the disc compatible with all DVD players. Other configurations include double layer DVDs (DVD-9) and two-sided discs (DVD-10, DVD-14 or DVD-18). Some labels are releasing DVD titles that are formatted as DVD-Audio on one side and DVD-Video on the other, the DualDisc being one such example.
[4]ELS Surround and Mark Levinson are two of the few vehicle audio systems which can play DVD-A.
Preamplifier/Surround Processor interface
In order to play DVD-Audio, a preamplifier or surround controller with six analog inputs was originally required.[5] 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 analog form and distribution to speakers, DVD-Audio is not allowed to be delivered via unencrypted digital audio link at sample rates higher than 48 kHz (i.e., ordinary DVD-Video quality) due to concerns about digital copying.[5]
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 High Definition Multimedia Interface (HDMI 1.1) also allows encrypted digital audio to be carried up to DVD-Audio specification (6 × 24-bit/96 kHz channels or 2 × 24-bit/192 kHz 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 analog cables.
- The 6 audio channels can be decrypted and then re-encrypted into an HDMI or IEEE-1394 (Firewire) signal and sent to the amplifier, which will then decrypt the digital signal and then extract the 6 channels of audio. HDMI and IEEE-1394 encryption are different from the DVD-A encryption and were 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 unauthorized 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.
- 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. There also exists an option to equip a DVD-A player with multiple S/PDIF outputs, for full resolution multichannel digital output. See: Six channel S/P-DIF output board.
Sound quality
From a purely technical standpoint, the audio resolution of a DVD-Audio disc can be substantially higher than standard red book CD audio. DVD-Audio supports bit depths up to 24-bit and sample rates up to 192 kHz, while CD audio is 16-bit, 44.1 kHz. In both cases, the source recording may have been made at a much higher bit and sample rate, and down-converted for commercial release.
Many DVD-Audio releases are older, standard definition audio recordings that have been remixed in 5.1 and upsampled to DVD-Audio's higher resolution. However, the fidelity of the upsampled audio will be limited by the source material quality and may not exceed the quality of existing CD releases of the same albums. When new recordings are made using high-resolution PCM encoding, a substantial difference in fidelity can be achieved.
Three of the major music labels, Universal Music, EMI and Warner Bros. Records and several smaller audiophile labels (such as AIX Records and DTS Entertainment) have released or are continuing to release albums on DVD-Audio, but the number is minimal compared to standard CDs. New high-definition titles have been released in standard DVD-Video format (which can contain 2-channel Linear PCM audio data ranging from 48 kHz/16-bit to 96 kHz/24-bit), "HDAD", which includes a DVD-Video format recording on one side and DVD-Audio on the other, CD/DVD packages, which can include the album on both CD and DVD-Audio, or DualDisc, which can contain DVD-Audio content on the DVD side. 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, were re-released as a CD/DVD package or as a DualDisc.
Copy protection
DVD-Audio discs may optionally employ a copy protection mechanism called Content Protection for Prerecorded Media (CPPM).[6] 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 can also utilize digital watermarking technology developed by the Verance Corporation, typically embedded into the audio once every thirty seconds. If a DVD-Audio player encounters a watermark on a disc without a valid MKB, it will halt playback.[7] 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 2005[7] by tools which allow data to be decrypted or converted to 6 channel .WAV files without going through lossy digital-to-analog 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.
In 2007 the encryption scheme was overcome with a tool called dvdcpxm. In 12 February 2008 a program called DVD-Audio Explorer 2008 was released, containing aforementioned libdvdcpxm coupled with an open source MLP decoder.[8]
Like DVD-Video decryption, such tools may be illegal to use in the United States under the controversial Digital Millennium Copyright Act. While the Recording Industry Association of America has been successful in keeping these tools off websites, they are still distributed on P2P file sharing networks and newsgroups,[9] Additionally, in 2007 the widely-used commercial software DVDFab Platinum added DVD-Audio decryption, allowing users to backup a full DVD-A image to ISO.[10]
See also
References
- ^ "Understanding DVD-Audio" (PDF). Sonic Solutions. Retrieved 2007-07-12.
- ^ "SACD & DVD-Audio: Ultra-High-Resolution Music". Crutchfield Advisor. Retrieved 2007-07-12.
- ^ "What is DVD-Audio?". 5dot1.com. Retrieved 2007-07-12.
- ^ www.elssurround.com
- ^ a b "DVD-Audio Tutorial". TimeForDVD.com. 2002-06-05. Retrieved 2007-07-12.
- ^ Labriola, Don (2003-08-25). "Digital Content Protection, Part II". ExtremeTech. Retrieved 2007-07-12.
- ^ a b Robinson, Stuart M (2005-06-07). "DVD-Audio Copy Protection Defeated via WinDVD Software Hack". HighFidelityReview.com. Retrieved 2007-07-12.
- ^ "DVD-Audio ripper". Retrieved 2008-04-09.
- ^ "DVD-Audio's CPPM Circumvented". Slashdot.org. 2005-07-06. Retrieved 2007-07-12.
- ^ "DVDFab updated to support DVD-Audio/CPPM". Retrieved 2008-04-15.
External links
- The 4C Entity LLC – Licensors of the Content Protection for Prerecorded Media (CPPM) specification.
- "DVD-Audio versus SACD: Perceptual Discrimination of Digital Audio Coding Formats" (PDF) Audio Engineering Society Convention Paper 6086.