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What makes DTS so special?

by Guido Henkel

In my series of articles that I write for trade publication “Replication News”, which has just changed its name to “Media Line”, I thought it may be a good idea to take a look at the current audio standards on DVD, and get rid of some of the myths surrounding the DTS and Dolby Digital formats. Here is a reprint as it appears in the January issue of “Media Line”.


When Jurassic Park appeared in theaters in 1993, it was the first movie that supported a sound format that would henceforth be known as DTS (Digital Theater Sound). Slowly it would permeate movie theaters as well as home theaters.
But with the new format came some controversy and a lot of confusion, which is becoming increasingly important as DVD is moving into more homes and many new DVD players carry the small DTS logo on the front.
DTS' purpose was to improve on the existing multichannel sound formats that were in use, and to get rid of some of the deficiencies inherent in these formats. It has since carried its torch into many home theaters as well, in an attempt to supersede the PCM audio tracks of audio CDs and laserdiscs--and, of course, the Dolby Digital tracks found on most DVDs. Despite the company's efforts however, DTS titles have yet to be considered more than niche titles, mostly due to the price tags attached to both the DTS releases and the equipment required to play back those tracks.

Another reason is that DTS has never become an "official" format of any medium. Although the DVD specifications define a flag to identify DTS tracks, the only "official" audio formats for DVD are PCM and Dolby Digital. As such, DTS is strictly an optional format on DVD, and as with any optional content, it is prone to misinterpretation and unrealistic expectations. At the same time it is of marginal interest to many content providers, as it requires additional effort, time and money to prepare an audio track that is only optional, while the existing standards sufficiently cover the demands and tastes of most consumers.

DTS is strictly
an optional format on DVD

In order to keep the bandwidth at bay that is required to play back a multichannel audio track, Dolby Digital uses a compression scheme that Dolby calls "Perceptual Encoding." It is based on an algorithm that enables one to squeeze more audio in a data
stream, while running the risk of degrading it to a degree. In general, DTS does exactly the same thing, but it utilizes a scheme that can keep more of the original's signal intact. DTS calls this scheme "Coherent Acoustics Coding," but the claims that
it delivers "master quality" and that it represents a sonic "clone" of the original are pure marketing tirades, as the terms "master" and "clones" themselves both would not allow any degradation whatsoever. Also the militant use of the word 'encoding'
rather than 'compression' doesn't change the fact that both Dolby and DTS formats actually compress and alter the original source.
It is from these kinds of marketing buzzwords and the terminology where much of the consumer confusion stems from. Many people are of the opinion that DTS audio tracks, for example, are implicitly of higher quality than Dolby Digital tracks, or that
Dolby Digital tracks are generally of poor quality--both of which are untrue. Especially in a movie environment, the challenge is not nearly as big as it may appear.

With the current release of DTS hardware and software to the public, it may only be a matter of time when we will hear the first collapsing DTS tracks.
 

Although sonic bleeding and channel collapsing can be a problem in Dolby Digital tracks, a well-done Dolby Digital production is generally able avoid these problems. (Editor: Sonic bleeding and channel collapsing are audible artifacts where the channel separation of the signal is lost or degraded, and an audio track loses a big part of its spatial integration.) Dolby Digital is also fully capable of  reproducing audio elements without "sonic degradation," to use DTS' own marketing terminology. For the most part it all depends on the source material. At the same time, low DTS bitrates can seriously degrade a signal in the same way, and especially with the current release of DTS hardware and software to the public, it may only be a matter of time when we will hear the first collapsing DTS tracks.

Certainly the biggest problem in the quality perception of Dolby Digital versus DTS is that most comparisons are not made on a level playfield. People compare poor Dolby Digital productions with the best DTS tracks they have access to, which of course
reveals some significant differences. It's like comparing the image quality of a MPEG-1 encoded Video CD with the best DVD there is, assuming they have to be similar because they're both coming on a shiny disc.

However, if you compare the high end from both sound formats, differences are becoming increasingly small, if not inaudible. While many consumers claim to be able to distinguish DTS tracks from Dolby Digital tracks, for the most part they are simply
caught up in the marketing machinery of an industry that bombards them with catch-phrases, buzzwords and comparisons that are taken out of context. Of course a DTS 5.1 production has a phenomenally superior spatial integration when compared to a
traditional stereo track. But so does every other current multi-channel format. Without diminishing anyone's merits, consumers often fail to see that marketing is the art to convince people that a company owns the Holy Grail and consumers need to buy
it.

As a webmaster of the Internet's most popular DVD site (www.dvdreview.com), I am often confronted with heated discussions and arguments surrounding the two sound formats--and sadly I have noticed that many people determine the quality of a surround
track by how much of a workout their omni-directional subwoofer gets during a movie.
It is also peculiar that with the stellar rise of DVD, DTS is mostly touted in the domain of the home theater movie experience in recent times. Contrary to what many people believe, movies are by no means an audiophile platform, where many of the
benefits DTS really has to offer can play off their strengths.

The sonic bed of any movie is made up of three layers of aural elements. The majority of it is dialogue, which is implicitly narrow-banded, by nature easy to compress and usually very front-loaded without much of a spatial integration that could lead to
bleeding or collapsing. Another layer is made up of the movie's sound effects: a barrage of noises that, as the name suggests, is enhanced for effects purposes. The majority of these effects are also made up of narrow-banded elements that are almost
arbitrarily placed in the sound field to create a surround experience. However, these elements can have a very high dynamic range.

The sonic bed of any movie is made up of three layers of aural elements and only one of them demands sonic excellence

Only the third aural layer of movies really demands sonic excellence--the music score. It usually requires good dynamics, a good and wide-banded frequency response, and a spatial integration that is realistically reproduced. But sadly, this element is
usually understated so as not to drown out the dialogue, and is periodically also overlapped by sound effects. Depending on the focus and quality of these three layers, DTS can indeed increase the quality of a presentation, but for the majority of films, Dolby Digital can achieve just as high a sonic representation.

What is interesting in this scenario is the fact that movies that would really benefit from DTS' increased quality are conspicuously absent from the roster of DTS titles. Films like “Amadeus”, “Immortal Beloved” and many other movies could dramatically
benefit from DTS' capabilities and the increased resolution that could allow for absolutely natural reproduction of the subtle and highly detailed recordings. While it is nice to see Universal's or Dreamworks' increasing commitment to DTS, neither
“Daylight” nor “Liar Liar” are titles that make use of DTS' full capabilities, and appear more as a general support for the format than an offer for a more audiophile experience.

There is an area where DTS can truly shine, and that is in multi-channel music recordings

Besides all this, there is an area where DTS can truly shine, and that is in multi-channel music recordings. Only a handful of titles are available at this point, but the increased clarity and definition in these titles can make a distinguishable difference, depending on the material and the overall production values. But it is in this field that DTS will face a tough challenge in the future. The emerging DVD-Audio format is by default a high-end format where sonic restrictions won't apply.

Completely without any degradation of the signal, DVD-Audio meets and exceeds the expectations of even the most audiophile listeners. The only thing DTS can add to this mix is an increase in playing time by using a different compression algorithm that yield's a better compression ratio than Meridian's MLP (Meridian Lossless Packing) scheme, which has been included in the DVD-Audio specification. But only if this compression scheme is also based on a lossless algorithm will DTS be able to maintain its current position as a format for audio enthusiasts.

DTS' position in the market is a tough one, and although the format has many fans, its true market penetration and acceptance is rather low. The fact that most DTS-enabled DVDs come at a significant premium doesn't help, and to make things worse, the
number of titles are very limited with no serious broadening of the palette in sight. One of the biggest hurdles in the race for consumer acceptance in the DVD arena is also the fact that at a premium price, most DTS titles come with a reduced set of
extras as opposed to their Dolby Digital counterparts. Universal is taking an interesting approach to the format as of late, by adding Dolby Digital and DTS audio tracks to some of their day and date releases, which by nature usually come with very
limited supplements.

While the differences between Dolby Digital and DTS soundtracks can be obvious in a direct comparison, it is hard to determine-or diminish--the quality of a track without such reference. As long as DTS is an option that has to be afforded by hard cash,
most consumers will be happy with Dolby Digital soundtracks--and rightfully so. At the same time, it has always been expensive to be a truly demanding audiophile listener, and that will never change. As such, it is once again one of DVD's great strengths that it manages to bring these two worlds together with ease, giving consumers and content providers a choice without necessarily ruling each other out.

This article has originally been published in “Media Line” and is reprinted here by permission.

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 February 2, 2000

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