DVD-Audio
DVD-Audio is a format for delivering high-fidelity audio content on a DVD. It offers many channels (from mono to 5.1 surround sound) at various sampling frequencies and sample rates. Compared to the CD format, 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 vertical bit-rates, and/or additional channels for spatial sound reproduction).
Audio on a disc can be 16, 20 or 24 bit, with sampling rates of 44.1, 48, 88.2, 96, 176.4 or 192 kHz. (The highest sampling rates of 176.4 and 192 kHz are limited to two channels.) Different sampling sizes and frequencies can be used on a single disc. Audio is stored on the disc in LPCM format (uncompressed or losslessly compressed with Meridian Lossless Packing). The DVD-Audio player may downmix surround sound to two-channel stereo if the listener does not have a surround sound setup. The downmix capability is limited to two-channel stereo, not to other configurations, such as 4.1. DVD-Audio may also feature menus, text subtitles, still images and slideshows. Inclusion of DVD-Video also is possible. Such discs commonly contain Dolby Digital or DTS versions of the audio (with lossy compression, usually downsampled to lower sampling sizes and frequencies) in the DVD-Video section. This is done to ensure compatibility with DVD-Video players.
A "hybrid" DVD-Audio disc (HDAD) contains a standard audio track (e.g., 24 bit/96 kHz) on one side, playable on any DVD-Video player. The other side contains the same content with a higher sampling rate, such as 24 bit/192 kHz, playable only a compatible DVD-Audio player. High fidelity DVD-Audio is never output in digital format by DVD-Audio players, to discourage digital copying. DVD-Audio players have six analog outputs, one for each audio channel (left, right, center, left surround, right surround, and Subwoofer). DVD-Audio players requires a compatible Surround sound amplifier, with the same six analog inputs, to play program material in surround. Otherwise, it is quite possible to use the format to play stereo recordings at high resolution with an ordinary stereo amplifier.
The introduction of the DVD-Audio format angered many early adopters of the DVD format. While DVD-Audio discs are capable of higher fidelity sound than CDs, there is debate as to whether or not the fidelity above 48 kHz is distinguishable to typical human ears. However, 24 bit recordings at 44.1 kHz and 48 kHz are widely accepted to be of substantial improvement to the 16 bit recordings currently available on Compact Discs. DVD-Audio currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment and a lack of education regarding higher fidelity and multichannel music. DVD-Audio is currently in a format war with SACD. DVD-Audio might find more success in the form of DualDisc and CD/DVD packages than as a standalone format, although newer formats such as HD-DVD and Blu-ray may render the format obsolete.
Copy prevention
DVD-Audio discs employ a robust copy prevention 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 also can utilize digital watermarking technology developed by the Verance Corporation.
As of 2005, CPPM has not been cracked. However, tools have been developed that will patch into a commercial software player and use it as middleware to decrypt the contents of the disc.
The 4C Entity also developed a similar specification, Content Protection for Recordable Media (CPRM), which is used on Secure Digital cards.
References
Labriola, Don. (August 25, 2003). Digital Content Protection, Part II. ExtremeTech.com
External links
- The 4C Entity LLC - licensors of the Content Protection for Prerecorded Media (CPPM) specification