DVD-Audio (commonly abbreviated as
DVD-A) is a digital
format for delivering
high-fidelity audio content on a
DVD. DVD-Audio is not intended to be a video delivery
format and is not the same as
video DVDs
containing concert films or music videos. The first discs entered
the marketplace in 2000. 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.
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. (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
depth/sampling rate/channel combinations:
| |
16-, 20- or 24-bit depth |
| 44.1 kHz |
48 kHz |
88.2 kHz |
96 kHz |
176.4 kHz |
192 kHz |
| Mono
(1.0) |
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| Stereo
(2.0) |
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| Stereo (2.1) |
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| Stereo + mono surround (3.0 or
3.1) |
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| Quad (4.0 or
4.1) |
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| 3-stereo (3.0 or 3.1) |
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| 3-stereo + mono surround (4.0 or
4.1) |
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| Full
surround (5.0 or 5.1) |
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Different bit depth/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
bit rate 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 (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.
Since the DVD-Audio format is a member of the DVD family, a single
disc can have multiple layers, and even two sides that contain
audio and video material. A common configuration is a single-sided
DVD with content in both the DVD-Video (VIDEO_TS) and DVD-Audio
(AUDIO_TS) directories. The high-resolution, Packed PCM audio
encoded using MLP is only playable by DVD players containing
DVD-Audio decoding capability. DVD-Video content, which can include
LPCM, Dolby or DTS material, and even video, makes the disc
compatible with all DVD players. Other disc configurations may
consist of double layer DVDs (DVD-9) or two-sided discs (DVD-10,
DVD-14 or DVD-18). Some labels have released two-sided DVD titles
that contain DVD-Audio content on one side and DVD-Video content on
the other, the Classic Records
HDAD being one
such example.
Preamplifier/Surround Processor interface
In order to play DVD-Audio, a preamplifier or surround controller
with six analog inputs was originally required. 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.
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.
There is controversy regarding the audible fidelity improvement
when listening to a stereo DVD-Audio disc compared to a CD-disc,
even when conditions and content are optimal. In a peer-reviewed
blind listening test published in the Journal of the Audio
Engineering Society, the authors were unable to find any proof that
stereo DVD-Audio as a format sounds different from CD. The author
suggests that differences in the mastering for particular DVD-Audio
and CD may explain perceived differences.
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). 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. 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 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 was released,
containing aforementioned libdvdcpxm coupled with an open source
MLP
decoder.
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,
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.
DVD-Audio authoring software
Normal DVD(Video) authoring software usually does not support
DVD-Audio creation, so there is some special software:
Macintosh
- Sonic Solutions DVD Creator AV – The first DVD-Audio
authoring solution available. A spin off of the popular high end
DVD Video authoring package. It allows DVD-Audio authoring at the
command line level only. Still widely used but no longer sold or
supported by Sonic Solutions.
- Sonic Studio SonicStudio HD – Macintosh based tool used
for High Density audio mastering and to prepare audio for DVD-A
authoring in One Click DVD.
- Sonic Studio
- Sonic OneClick DVD – Converts prepared Sonic Studio EDLs
into binary MLP files to be used in the authoring tool. Also
generates scriptFile information to be added to DVD Creator AV
projects.
- DVD audio Tools: console application dvda-author (version
08.07), see below.
- Apple Logic Pro 8 - When bouncing, choose "CDDA" under
destination, and then choose DVD-A from the popup menu.
- Minnetonka discWelder Bronze is now available for Macintosh.
Very simple to use if you just want to burn your own files to
listen to in this format.
Windows
Linux
- A project called DVD audio Tools provides free/open source
DVD-Audio authoring tools for Linux and other *nix platforms
(FreeBSD, OpenSolaris,...).
Windows (console application) binaries are also available.
DVD-Audio/Video discs (aka Hybrid or Universal DVDs) are also
supported.
See also
Other high fidelity disc formats:
References
- Meyer, Brad. Audibility of a CD-Standard A/D/A Loop Inserted into
High-Resolution Audio Playback. Journal of the Audio
Engineering Society (Engineering Reports).
- http://www.sonicstudio.com
- http://www.minnetonkaaudio.com/products/discwelder01.html
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