Hi Fi Writer - DVD Audio and SACD explained

DVD Audio and SACD explained

This version: 20 November 2003, previously published in Appliance Retailer, March 2002

Note: This was written primarily as an educational piece for retail staff. Read it in that light.
Please also see my more up-to-date comments.

The world of digital sound is getting complicated. For fifteen years there was just one digital format: the CD. Now with MP3 taking over computers, and DVD taking over TV screens, there are two more audio formats with which to contend. These are DVD Audio and the Super Audio CD.

What are they?

DVD Audio and SACD are both 12cm discs that look just like CDs or standard DVDs. However they work differently from each other and, for the moment, require different players. Yet both are intended as super high quality music discs. Yes, both are designed for music, not video.

They are intended to overcome what some audiophiles perceive as inherent deficiencies in the CD format. While the CD employed very advanced digital technology on its introduction in the early 1980s, the digital world has moved on. DVD-A and SACD allow a digital resolution of the musical signal around 250 times higher than the CD, and extend the high frequency response well beyond CD's limit of just over 20,000 hertz (which is generally regarded as the upper limit of human hearing).

Most consumers will not notice these technical quality improvements. But they will notice the other enhancement: both DVD-A and SACD support six channel surround sound. For this to be enjoyed the players have to be connected to a suitable surround sound system with six channel inputs. Unlike CDs and DVD Videos, the sound from SACDs and DVD-As will not travel down a digital connection (this was barred by the developers to prevent digital copying).

Since surround sound is already available from DVD Videos, what's the advantage of SACD and DVD-A? The surround sound on standard DVDs is in a compressed format: either Dolby Digital or DTS. These are both 'lossy' forms of compression in which some of the musical signal (thought to be inaudible) is dispensed with in order to realise huge space savings. There is some dispute about which of these is better than the other, but there is no doubt that both are inferior to SACD and DVD-A.

How do DVD-A and SACD compare with each other?

DVD-A and SACD use different encoding techniques for their high quality sound. For DVD-A this is MLP (see the Glossary for these terms), sometimes called PPCM. SACD uses DSD. Neither is compatible with the other, but record companies that record in either system can convert to the other with no loss of quality (the audiophile US label Telarc does this). Of more relevance to the consumer is their differences in compatibility. DVD-A content is only playable on a DVD-A player. SACD is only playable on an SACD player. Both players are, at this stage, fairly pricey items (around $1,200 RRP for DVD-A and $1,000 for SACD at the time of writing). Prices will fall fast of course.

Fortunately the developers of both formats realised that this limited compatibility would be a drawback in the market place. Almost all DVD-A discs are therefore released with standard DVD-Video content as well so they'll work in regular DVD players. This content is a straight copy of the main DVD-A program (which, remember, usually only has sound and still pictures), but any special extras normally aren't included. The DVD-Video portion usually has its sound recorded in Dolby Digital or DTS 5.1.

SACD discs, in contrast, are almost all designed to be compatible with standard CD players as well. They have no video content at all (specialised SACD players don't have a video output). These discs are dual layer – like the dual layers of many DVDs, but with the SACD audio on one layer and a standard CD version on the other. Stick it in a standard CD player and the CD version plays.

Will DVD-A or SACD win in the marketplace?

The near-simultaneous introduction of two formats could be seen as a re-run of the Beta vs VHS fiasco of a quarter century ago. But it won't be. The reason is that Beta and VHS videos were mechanically incompatible. This isn't the case with DVD-A and SACD. All current DVD-A players will also play standard CDs and DVD videos. The less expensive SACD players will also play standard CDs and DVD Videos. Expect within a year to see players that support DVD-A, SACD, CD, DVD Video and, probably, MP3 playback from CD-Rs ... all in the one box. The laser mechanisms are the same. The players just need more integrated circuits to deal with all situations. As is the way of these things, they'll be expensive at first, then cheap and ubiquitous. Already Pioneer has a player supporting DVD Video, DVD Audio and two channel SACD available in the United States (for a modest $US5,999).

Tips

One problem with most DVD Videos is the time they take to start, what with copyright notices and menus to navigate. DVD Audios share these, but they can be easily bypassed and the music played without even any need to switch on a TV. After the disc is placed in the tray of a DVD-A player, instead of pressing the 'close' button, press the 'play' button. The tray will close and the program will immediately start playing, just like a regular CD.

To get the best surround sound performance from either system, go into the setup menu and adjust the speaker settings to match the speakers being used. The player's manual will explain how.

Glossary

DSD – Direct Stream Digital, the digital encoding technique used for SACD. This is a one bit system operating at over two megahertz, with the frequency of the bits representing the analogue signal.

MLP – Meridian Lossless Packing, the digital encoding technique used for DVD Audio. This is based on the PCM system used for CDs, but uses a higher sampling frequency (typically 88.2kHz or 96kHz for six channel signals and up to 192kHz for stereo signals, compared with CD’s 44.1kHz) and greater resolution (up to 24 bits, compared with CD’s 16, yielding 256 times CD’s resolution). It also employs a special compression technique developed by the British company Meridian which, unlike Dolby Digital and DTS, preserves the original signal perfectly.

PCM – Pulse Code Modulation, the oldest and most commonly employed digital encoding technique. A sample of the analogue signal is taken many thousands of times each second, and its level is mapped onto a digital number.

PPCM – Packed Pulse Code Modulation, another term for MLP.

DVD Audio vs SACD

	DVD-A	SACD
Physical	12cm disc like a standard DVD or CD	12cm disc like a standard DVD or CD
Construction	Single (4.7GB) or dual (8.5GB) layer	Single (4.7GB) or dual (4.7GB plus CD content) layer
Digital encoding	MLP	DSD
Supports video content	Yes	No (there is provision for video in the specification, but it has not been implemented)
Audio content supported	Six channels at 96kHz/24 bit,Two channels at 192kHz, 24 bit, DVD video content	Two or six channels using DSD encoding, CD content (on dual layer discs)
Advantages	Most DVD-A discs can be played on standard DVDs with lower audio quality, although still in surround sound	Most SACD discs can be played on standard CD players with lower audio quality, limited to stereo
Types of players available	Combination DVD Audio/Video players; Universal Disc Players	SACD-only players; combination SACD/DVD Video players (some early SACD-only players were stereo only); Universal Disc Players