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DVD-Audio is a digital format for delivering very 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. Since media players that can play many formats (including DVD-Audio and SACD) are available for under $100, both formats are likely to co-exist (as do DVD-R and DVD+R).

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. 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.

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 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. A criticism of DVD-Audio and SACD is that both require the listener to be near a home stereo system as one cannot rip either format to portable MP3 players. As of 2006, very few car stereos are capable of playing DVD-Audio discs.

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 an 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 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 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 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:

1. The 6 audio channels can be decrypted and extracted in the player and sent to the amplifier along 6 standard analogue cables.
2. 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 to 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.
3. 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.

4. 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 can be substantially higher than a standard red book CD audio. DVD-Audio supports bit depths up to 24-bit and sample rates up to 192kHz, while CD audio is 16-bit, 44.1kHz. In both cases, the source recording may have been made at a much higher bit and sample rate, and down-converted for commercial release.

It is uncertain whether average listeners can hear the difference between DVD-Audio and CD-Audio, and many consumers do not regard any supposed quality improvements offered as sufficient reason to justify purchasing new playback equipment and repurchasing albums in higher-resolution 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.

Wikipedia information about DVD-Audio
. This article is licensed under the GNU Free Documentation License . It uses material from the Wikipedia article 'DVD-Audio'

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