3.6.1 DVD-Audio details
Description
This article is from the DVD Formats FAQ, by jtfrog@usa.net (Jim Taylor) with numerous contributions by others.
3.6.1 DVD-Audio details
LPCM is mandatory, with up to 6 channels at sample rates of 48/96/192 kHz
(also 44.1/88.2/176.4 kHz) and sample sizes of 16/20/24 bits. This allows
theoretical frequency response of up to 96 kHz and dynamic range of up to
144 dB. Multichannel PCM is downmixable by the player, although at 192 and
176.4 kHz only two channels are available. Sampling rates and sizes can
vary for different channels by using a predefined set of groups. The
maximum data rate is 9.6 Mbps.
The WG4 decided to include lossless compression (it's about time!), and on
August 5, 1998 approved Meridian's MLP (Meridian Lossless Packing) scheme,
already licensed by Dolby. MLP removes redundancy from the signal to
achieve a compression ratio of about 2:1 while allowing the PCM signal to
be completely recreated by the MLP decoder (required in all DVD-Audio
players). MLP allows playing times of about 74 to 135 minutes of 6-channel
96kHz/24-bit audio on a single layer (compared to 45 minutes without
packing). Two-channel 192kHz/24-bit playing times are about 120 to 140
minutes (compared to 67 minutes without packing).
Other audio formats of DVD-Video (Dolby Digital, MPEG audio, and DTS,
described below) are optional on DVD-Audio discs, although Dolby Digital is
required for audio content that has associated video. A subset of DVD-Video
features (no angles, no seamless branching, etc.) is allowed. It's expected
that shortly after DVD-Audio players appear, new universal DVD players will
also support all DVD-Audio features.
DVD-Audio includes specialized downmixing features for PCM channels. Unlike
DVD-Video, where the decoder controls mixing from 6 channels down to 2,
DVD-Audio includes coefficent tables to control mixdown and avoid volume
buildup from channel aggregation. Up to 16 tables can be defined by each
Audio Title Set (album), and each track can be identified with a table.
Coefficients range from 0dB to 60dB. This feature goes by the horribly
contrived name of SMART (system-managed audio resource technique). (Dolby
Digital, supported in both DVD-Audio and DVD-Video, also includes
downmixing information that can be set at encode time.)
DVD-Audio allows up to 16 still graphics per track, with a set of limited
transitions. On-screen displays can be used for synchronized lyrics and
navigation menus. A special simplified navigation mode can be used on
players without a video display.
Sony and Philips are promoting SACD, a competing DVD-based format using
Direct Stream Digital (DSD) encoding with sampling rates of up to 100 kHz.
DSD is based on the pulse-density modulation (PDM) technique that uses
single bits to represent the incremental rise or fall of the audio
waveform. This supposedly improves quality by removing the brick wall
filters required for PCM encoding. It also makes downsampling more accurate
and efficient. DSD provides frequency response from DC to over 100 kHz with
a dynamic range of over 120 dB. DSD includes a lossless encoding technique
that produces approximately 2:1 data reduction by predicting each sample
and then run-length encoding the error signal. Maximum data rate is 2.8
Mbps.
SACD includes a physical watermarking feature. Pit signal processing (PSP)
modulates the width of pits on the disc to store a digital watermark (data
is stored in the pit length). The optical pickup must contain additional
circuitry to read the PSP watermark, which is then compared to information
on the disc to make sure it's legitimate. Because of the requirement for
new watermarking circuitry, SACD discs are not playable in existing DVD-ROM
drives.
SACD includes text and still graphics, but no video. Sony says the format
is aimed at audiophiles and is not intended to replace the audio CD format.
A special dual-layer format that would allow SACDs to play in existing
compact disc players was originally planned, but was dropped in 1999
because of technical problems. It may be revived when yields are high
enough that it no longer costs more to make a hybrid SACD disc than to
press both an SACD DVD and a CD. See 1.12 for player info.
See E-Town's two-part DVD-Audio vs. SACD article for more on DVD-Audio and
SACD.
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