This article originally appeared in the June 1999 issue of EQ Magazine.

Now that DVD is becoming commonplace on the shelves of the local electronics superstore, two new formats also are about to enter the lexicon of the consumer and this time they're audio specialty items. The DVD-Audio disc and Super Audio CD (SACD) are getting more and more press these days so we decided to give you a quick but thorough overview as to what to expect from, and how to prepare for each format.

Some Background First

Before we talk about DVD-A and even SACD (since they're loosely related), some DVD basics are in order. The DVD distinguishes itself from a CD in two ways; storage capacity and file system.

Storage Capacity

While the storage capacity of a current CD is 650MB, the capacity of a DVD can actually be one of four levels, all far exceeding the CD. This is accomplished by having more and smaller pits on the substrate than that of a CD. Add to this the fact that DVD can have two layers and be double sided, and the power of DVD becomes readily apparent. (FIGURE 1) Because a laser with a smaller wavelength is required, a CD player cannot read a DVD. A DVD player can read a CD though.

FIGURE 1 - DVD TYPES AND CAPACITIES

Please Note: There's some unfortunate confusion as to the actual capacity of a DVD because it's measured differently than the computer norm. For example, a DVD-5 has 4.7 billion bytes (G bytes) not 4.7 gigabytes (GB). The problem is that DVD is based on multiples of 1000 while the computer world measures bytes in multiples of 1024. Therefore, a DVD-5 actually has a capacity of 4.38 gigabytes.

File Format

Today's CD can be thought of as essentially a "bit bucket" in that there is no intelligence built into the different file formats required for audio CD, CD-ROM, CD-R, etc. DVD differs in that the various types use basically the same DVD-ROM-like format with a bit of intelligence built into the specification.

DVD uses a file format known as Universal Disc Format or UDF which was designed specifically for use with optical medium and avoids the problems and confusion that CD-ROM's had because of the many different file formats used. In fact, UDF permits the use of a DVD by DOS, OS/2, Macintosh, Windows and UNIX operating systems as well as dedicated players. What's interesting is that a dedicated DVD player will access only the information that it requires and all other files will remain invisible. It also means that the file system for use with computers is already built into the format, which widens the potential market without having to jump through programming hoops.

DVD-V Basics

DVD-Video burst upon the scene two years or so ago primarily as a high quality movie delivery system, but the audio portion of the format is still quite an improvement over the Red Book CD standard. And because there's automatic provisions for multichannel audio and a built-in (but limited) 96/24 option, DVD-V may yet become a major delivery format for audio before all is said and done.

Sonics

The audio portion of a DVD-V can have up to eight bit streams (audio tracks). These can be 1 to 8 channels of common Linear PCM (LPCM), 1 to six channels (5.1) of Dolby Digital, or 1 to eight channels (5.1 or 7.1) of MPEG-2 audio (FIGURE 2). Also, there are provisions for optional DTS or SDDS encoding as well.

The LPCM bit stream, which is the same uncompressed format as today's Red Book CD (which is standardized at 44.1kHz and 16 bit), can use either a 48 or 96kHz sample rate with a bit depth of either 16, 20 or 24 bits. Now on the surface this seems great and makes you wonder why another format for multichannel audio is even considered, but then you realize that the bit rate for the audio data is capped at 6.144Mbps. The bit rate (sample rate X number of bits X number of channels) is equivalent to the size of the pipe that the audio data has to flow through and in this case the pipe isn't big enough to fit 6 channels of 96/24 audio. In fact, all you can squeeze through is 2 channels of 96/24. If you want multichannel, you're back at 48k but at least the bit depth is raised to 20 bits for six channels. (See FIGURE 2) So now we have to go to some sort of data compression scheme to fit all of the channels down the pipe at a higher audio quality.

FIGURE 2 - AUDIO PORTION OF A DVD-VIDEO

The standard compression scheme for DVD-V is Dolby Digital (or AC-3) which compresses six channels (5.1) of up to 24 bit audio to fit through the DVD-V audio pipe but is limited to only a 48kHz sampling rate. Plus it is a lossy compression algorithm with a maximum bit rate of 448kbps (although 384 is mostly used) which means that some data is thrown away in the encoding process (although the goal is to only throw away the data that you won't miss). MPEG-2 Audio, which can be configured either six channel (5.1) or eight channel (7.1) at 48/16, is also an optional compression scheme but hardly used (especially in the US) due to lack of decoders in the marketplace. Even though MPEG-2 does have a higher bit rate at 912kbps, the algorithm has its share of inherent coding problems, which effectively negates its lower data compression.

Although an optional coding process, DTS encoding can also prove to be an interesting choice since it can potentially encode up to 8 channels of 96/24 with less data compression than either Dolby Digital or MPEG.

Just What Is DVD-Audio?

The DVD-Audio disc should be in the stores by Christmas and there's a lot to like about it. The main feature and difference between DVD-A and its video cousin is the ability to provide significantly higher audio quality. Just having the ability to do so doesn't necessarily mean that the highest fidelity audio will happen though, because for better or worse, the final decision as to the sonic quality is largely in the hands of the content producer.

Sonics

DVD-A differs from the audio portion of DVD-V in that the data pipe is a much larger 9.6Mbps compared to DVD-V's 6.144Mbps. Even with the wider audio pipe, six channels of 96/24 LPCM audio still exceeds the allotted bandwidth (multiply 96k by 24 bits x 6 channels to get the resultant 13.824Mbps bandwidth). Therefore, there needs to be some type of data compression to not only fit the required amount of data through the pipe, but increase the playing time as well.

For this requirement, MLP (Meridian Lossless Packing) was selected as the standard data compression for DVD-A. MLP, which gives about a 1.85 to 1 compression ratio, is seemingly lossless, meaning that no data is thrown away during the compression process. Dolby Digital is listed as a lossy compression option. Also possible is the use of other coding technologies besides LPCM such as DSD and DTS.

Of special note is the fact that DVD-A is also what is known as Extensible. This means that it's relatively open-ended and can utilize any new audio coding technology that becomes popular in the future.

Scalability

One of the neat and possibly confusing traits about DVD-A is what's known as Scalability, which is a 25 cent word for "Lots of options". Audio-wise the list of options is truly extensive. The program producer is able to choose the number of channels (1 to 6), the bit depth (16, 20, 24) and the sample rate (44.1, 48, 88.2, 96, 176.4 or 192kHz) See FIGURE 3. What's more, the producer can also mix and match different sample rates with different bit depths on different channel families. For example, the front three channels (family 1) can be set to 96/24 while the rear (family 2) and sub channels are set to 48/16. This is important for more efficient bit budgeting if additional space for videos or stereo mixes is required.

FIGURE 3 - DVD-A AUDIO SCALABILITY

Playback Time

Even with DVD-A's increased storage capacity, there's still not enough room to contain 74 minutes of discrete multi-channel Linear PCM (LPCM) program at the high sample rates and bit depths. So the option exists to compress the audio data several ways.

As stated before, for the high sample rates and bit depths (88.2, 96, 176.4 or 192kHz/24 bit) Meridian Lossless Packing, or MLP, is provided. This method is attractive in that it can almost double the playing time with supposedly no loss in data and therefore audio quality (See FIGURE 4). For the lower sample rates and bit depth (48k/20 bit), Dolby Digital (AC-3) is also provided as an option.

FIGURE 4 - APPROXIMATE PLAY TIME FOR A DVD-5

SMART Content

One of the more interesting aspects of DVD-A is a new feature known as SMART (System Managed Audio Resource Technique) Content. SMART Content is an auto downmix provision that lets a consumer with only a stereo system have the multichannel mix automatically downmixed to that format. In other words, the 6 channel 5.1 mix automatically becomes a stereo mix if there's only two channels in the playback system. While on the surface it might seem like a scary thing having that great multichannel mix automatically fold down to stereo, SMART Content actually gives the producer a choice in the way this downmix will take place by allowing the producer to select one of 16 downmix coefficients that get stored along with the audio data. SMART Content has the added byproduct of potentially eliminating the need to include a separate stereo mix on the disc, thereby freeing up space for either higher quality audio or additional data information. While this looks good on paper, it's still too early to tell what it actually sounds like in practice.

Copy Protection

Of primary concern to all the committees and groups working on DVD-A was the inclusion of strong anti-piracy measures and copyright identification. In fact, the encryption and watermarking issues have actually taken the longest to resolve and have held up the release of the format until now. However, the encryption standard has already been decided upon and the watermarking issue should also be set in stone by the time you read this article, clearing the way for the format's introduction.

A point of concern regarding the inclusion of watermarking (which identifies the manufacturer, artist and copyright holder by embedding a digital code in the noise floor) has been about the possible degradation of the audio quality as a result. Having personally participated in the watermarking listening test, I can state with some certainty that watermarking is virtually undetectable even under microscopic studio conditions and should not prove to be a deterrent to audio quality in any way. In fact, watermarking should prove to be a boon to content owners in general since it will work on any digital transmission, including Web downloads, which should result in a lot less pirating and a lot more royalties. One thing is for sure, most record companies feel that watermarking is the key to their future survival in this increasingly digital world, and this portion of the spec will be absolutely ironclad before the format is released.

Value-Added Content

One of the attractive features of DVD-A is the ability to add additional content such as liner notes, music videos and even Web URLs that enable the consumer to access related material on the Internet when played from a computer's DVD-ROM drive. This could prove another immediate advantage since consumers have always complained about the lack of information found on CD's. Couple this with additional artist commentary, discographies promoting back catalog titles, bios, links to websites (and therefore aftermarket sales), and even a place to finally put those videos that MTV never played, and the value-added material could bring the format to life.

Each track (song) has the ability to display up to 20 still images that can run like a slide show in an automatic or manual mode. This can either be a great way to display artist or song information or a lame attempt to add some info that no one wants to see, depending on how it's implemented. Videos can also be added in the video portion of DVD-A providing there's sufficient room.

SACD: The Audio Beta?

Thanks to the promise of improved sonic performance as well as backwards and forwards compatibility, the Super Audio CD (SACD) is certainly an intriguing prospect in the multichannel delivery wars. With the massive corporate muscles of Sony and Phillips behind this format, SACD could well prove to be quite a formidable challenger in the multichannel sweepstakes. SACD's vision has actually changed somewhat from what was first announced, as the product that will initially be released will be scaled back in terms of features.

The SACD is a dual layer disc (basically a DVD-9) with one layer dedicated to normal Red Book CD-type audio and the second to a high density layer for a six channel surround mix, a two channel stereo mix, and potentially extra data such as text and graphics. What makes this interesting to the record companies is the ability to be both backwards and forwards compatible, meaning that consumers can play an SACD on their current CD player and play a current CD on a SACD player as well. Because of the requirement for new watermarking circuitry, SACD discs are not playable in existing DVD-ROM drives however.

Sonics

SACD touts an improvement in sonic quality due to a new twist in a current recording process known as Direct Stream Digital (DSD). DSD uses essentially the same delta sigma oversampling method used in most modern high-quality analog to digital conversion systems where a single bit measures whether a waveform is rising or falling rather than measuring an analog waveform at discrete points in time. In current systems, this one bit is then decimated into LPCM causing a varying amount (depending upon the system) of quantization error and ringing from the necessary brickwall filter. DSD simplifies the recording chain by recording the one bit directly, thereby reducing the unwanted side effects.

Indeed on paper SACD with DSD looks impressive. A sampling rate of 2.8224 MHz (which is 64 times 44.1k in case you're wondering) yields a frequency response from DC to 100kHz with a dynamic range of 120dB. Most of the quantization error is moved out of the audio bandwidth and the Brickwall Filter which haunts current LPCM systems is removed. To enable a full 74 minutes of multichannel 100/24 recording, Phillips has also developed a lossless coding method called Direct Stream Transfer that gives a 50% data reduction. Yet some critics speculate that DSD is a closed system with little room for improvement in that both the frequency response and dynamic range cannot be improved much beyond the current spec. Others note the fact that no data interfaces, DSP chips and little supporting software exist while their LPCM counterparts abound.

Other Data

As in DVD-A, text, graphics, but no video, can accompany the audio data. However, this will take the form of today's Blue Book "Enhanced CD" which doesn't look to be quite as elegant an implementation as the UDF file format utilized by DVD. In fairness, this area of SACD doesn't seem to have been given much thought since the disc is intended for the audiophile market. We may see some new features and execution as the format matures though.

Sony released an SACD player in Japan in May 1999 and expects a STEREO-only player to be available in the U.S. for $5,000 retail by the end of the year. SACD discs, like DVD-A's, are supposed to initially retail for $24.95, and later drop to a magic number of $19.95. The apparent reason for the stereo release is that there's no multichannel DSD recording and editing equipment available yet, even in prototype form.

What Do I Need To Get Going With DVD-A or SACD?

Working in either format is out of the league of the project, or even the average commercial studio at the moment. To take full advantage of the DVD-A format you would need the ability to record, mix and store at 96/24, which is currently not too widespread. This will change soon since almost the entire audio industry is waiting for the same converter chipset in order to implement their 96/24 features. Still, if you want to record at 192 or 176.4kHz, these converters are still prototypes so don't expect to see them readily available for some time. Authoring tools for DVD-A are available now from Sonic Solutions but this stage is relegated to the mastering facility and/or the authoring house.

So how can you get ready for DVD-A right now? Mix to eight track analog (no kidding!) and let the mastering house deal with the conversion to the digital domain. This will cost far less than buying any of the required hardware and software and will leave you with a robust archive master that will probably outlive most digital formats anyway. The downside is we're back to our old friend tape hiss again.

SACD is a different matter completely. Virtually all of the DSD gear at the moment is prototype only, so unless you have an in at Sony you've got a wait ahead. Even when the gear becomes available, it will mean that all of your current PCM based gear will be rendered useless! Plus it looks like there'll be only one vendor to buy from (Sony) for a while as well. But if DSD lives up to its highly touted audio quality, those wanting only the best will buy in with no second thoughts.

So if you're lucky enough to be on the cutting edge of technology, you probably have an immediate decision to make. For the rest of us mere audio mortals, its time to sit back for a while and watch and listen to the market make our decision for us.

DVD-AUDIO ADVANTAGES

Extensibility - Open technology has provisions for new innovations beyond LPCM in the future.

Scalability - The program producer chooses the number of channels, bit depth, sample rate, and encoding method.

Value Added Material - Liner notes, album cover artwork, music videos, artist commentary and Internet links can all be included.

Copy Protection - Strong encryption methods makes DVD-A harder to pirate than any previous digital medium. Watermarking provides easy copyright identification.

DVD-AUDIO DISADVANTAGES

Will the Consumer Accept Another Format? - Will 96/24 make enough difference to the average consumer to plunk down $5-600 on yet another piece of entertainment hardware?

Must Connect To A TV To Navigate - A television or video monitor is an integral part of disc navigation.

Lack of Moving Pictures During the Song - Many in the production community believe this to be a liability, even though up to 20 still pictures per song may be used. However, if material such as liner notes, artist/producer and even engineer bios and commentary are used, this could actually be a nice adjunct. After all, one of the main complaints about CD's was the lack of information relative to what was previously found on LP's. File this under, Too Early To Tell.

Some DVD-A Discs Won't Play In Some Current DVD Players - Since DVD-A was specified well after DVD-V hit the marketplace, DVD-A discs will not play on the first generation of players already out there.

SACD ADVANTAGES

Sonic Performance - Wide bandwidth goes from DC to 100kHz with a 120dB dynamic range. No adverse filter artifacts thanks to elimination of the brick wall filter. Widespread positive reviews regarding audio quality.

Plays on Current CD Players - With both backwards and forwards compatibility, consumers won't feel forced to buy expensive new hardware or give up their current libraries.

No TV Needed To Operate - Standalone player does not require connection to television to navigate.

SACD DISADVANTAGES

Yet Another Format - As with DVD-A, will the average consumer be willing to buy another piece of expensive hardware? Will consumers be confused with yet another format choice?

Is The Sonic Performance Really Better? - While DSD seems every bit the equal to the current state of LPCM, advances in converter technology could eventually move LPCM beyond the seemingly closed format of SACD.

New Production Equipment Needed - Because of the DSD technology, new production equipment, from recorders to editors to digital consoles, is required. Given the fact that LPCM equipment abounds worldwide, will the production community balk at the format?

Initially More Expensive - Not only will the production equipment be more expensive (some estimates are as much as 10 times LPCM), but initial player cost will be $5000 (for stereo only with no digital outputs).

Only Stereo At First - Both the players and discs will initially be released in stereo only.

No Value Added Material At First - The first discs will not have text or graphics, only music. In fact, the first discs may not even have a stereo Red Book layer, negating the backwards compatibility.