DVD-Audio vs. Super Audio Compact Disc

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Part 1.: A brief history of digital audio for consumers

In 1982, the Compact Disc was introduced to the marketplace as the format destined to replace vinyl records. The CD differed substantially from its predecessor in that it was the first digital audio format available to consumers, using a system known as Pulse Code Modulation or PCM to encode the audio signals. Advertisements at the time touted phrases like “Perfect sound – forever.” However, complaints soon started cropping up. Those who weren’t impressed by the new shiny discs complained of “harshness” and “lifelessness” – issues that were initially largely ignored. Although digital audio did alleviate many of the problems associated with analog media such as unwanted noise, irregular frequency response (a technical equivalent to timbre) and something called wow and flutter, eventually the manufacturers and other folks in the professional audio industry came to realize that there were a number of new problems unique to digital formats. Some of these issues were the product of technological limitations that have been either partly overcome or fixed entirely over the past 19 years. Still, there were a number of confines built into the CD format that could not be corrected without entirely changing its specifications.

In 1996, a new optical disc-based format called Digital Video Disc or DVD was introduced. This offered a number of advances in audio over the CD format – most notably the introduction of so-called 5.1-channel audio, also known as surround sound. Since the standard for film sound demands additional loudspeakers in front and to the sides of the audience, and since DVD was initially introduced as a medium for the distribution of video, the initial DVD discs and players offered separate outputs for five loudspeakers with full frequency ranges in addition to a Low Frequency Effects or LFE channel, which is produced by a low-frequency loudspeaker called a subwoofer. Since this channel is limited in its capabilities to produce only bass material such as explosions and thunder, it is called 0.1 of a channel, hence the label 5.1 channels.

One issue that is typically not discussed by many people is that although the initial DVDs (now called DVD-Video) have more audio channels available, each of those channels typically has a lower quality of sound than that on a typical CD. This is because almost all DVD-Videos make use of a compression scheme known as AC-3 or Dolby Digital in order to fit all that audio on a single disc alongside the video information. This compression is based on an algorithm that predicts which components of the audio signal you will be unable to hear because they’ll be psychoacoustically masked (a fancy term meaning “drowned out”) by other components in the same signal. The algorithm then decides that, since you’re unable to hear these components, they need not be on the recording in the first place.

This system works very well most of the time, particularly because you’re being distracted by the accompanying movie on the screen. However, problems arise when there are no distracting images and you are able to hear better than the compression algorithm predicts you can.

As a result, a new format based on the DVD platform, but restricted to high-quality audio, excluding video almost entirely, was introduced. After years of debate and committee meetings, this DVD-Audio was finalized in the spring of 1999. The DVD-Audio standard permits only the use of a compression algorithm known as Meridian Lossless Packing or MLP which, as its name implies, does not result in the loss of information as does the AC-3 scheme. Additionally, the audio quality of DVD-Audio is much higher than that of the CD.

As will be discussed in Part 2 of this article, the method used to encode the audio in DVD-Audio is essentially an upgraded version of the PCM used in the CD. It should also be noted that the DVD-Audio specification allows for up to six full-range audio channels, one of which can optionally serve as the LFE channel if desired.

The competition for the DVD-Audio format was created by the original developers of the CD and is dubbed the Super Audio Compact Disc or SACD. This was introduced as a two-channel stereo format in the fall of 1999 and as a six-channel format (which, again, can serve as a 5.1 system) in the spring of 2001. It is based on a very different method of digitally encoding the audio signals known as Direct Stream Digital or DSD.

So, for now, we have two competing formats, both vying to be the successor to the CD. With memories of the VHS vs. Beta war still fresh in our minds, many are reluctant to commit to one format or the other, and unfortunately, it is still too early to see which format will win. Oddly, it is possible for manufacturers to build a single machine that can play both DVD-Audio discs and SACD’s – in fact, one such player is available in stores at the moment. If all manufacturers were to do this, the issue of comparison would, of course, be irrelevant.; yet, due to marketing issues, it is unlikely that dual-format players will be the standard for some years to come, if ever.

In Part 2 of this article, we’ll look at how digital audio works and, more importantly, how PCM used in the DVD-Audio discs is different from DSD in the SACD’s.

Biography

Geoff Martin is a Faculty Lecturer in the Music Technology Area at McGill University’s Faculty of Music. He holds a PhD in sound recording, and maintains an active musical career as an organist, choral conductor and electroacoustic music composer.