FEEL THE NOISE: Dolby versus dts for DVD - Technology Information

Emedia Professional, July, 2000 by Michelle Manafy

The pursuit of art is in many ways a search for an experience outside our own. We seek complete transformation of our existence in great books, in music, and in paintings, though perhaps never been more palpably as in the case of film. The goal is immersion, which utterly transports the viewer into not just another place, but another reality. Each form has its own inherent advantages in achieving this goal, but film brings all of the pieces together--the images, the narrative, and the sound. In art, the choice of medium is often as important as message and this dictum holds true for film.

Losing oneself in the sound and fury of film has always been an essentially private pursuit, an individual journey not necessarily best taken in the crowded confines of a cinema. The advent of the VCR brought that experience home, but in personalizing the viewing experience, also diminished the visceral audio-visual punch that had made it so potentially engrossing in the theater. DVD, by contrast, brings it all home, ushering in a new era for film enthusiasts and with it a new expectation of both video and audio clarity. Surround sound promises not only an authentic theater experience at home, it offers more. It will deliver exactly what the filmmaker intended, right into our living rooms. No doubt, the lack of chattering, popcorn-eating, package-crinkling fellow theater-goers may for some enhance the audio experience of movie-going, but as with all things DVD, there are other competing factions vying for your attention. Format wars continue, and two types of surround sound that are used in movie theaters are also currently jostling for position in the home theater market: Dolby Digital and dts. Unfortunately, the two systems do not play well with each other, and the movie industry, authoring houses, and the consumers are left to choose one or both, hoping not to miss out on the next big thing.

WHAT'S IN A NAME?

The name Dolby is almost synonymous with good sound. In 1966, the first generation of Dolby noise reduction (A-type NR) was used in Decca professional noise reduction units; two years later, the Dolby B-type NR logo first appeared on a consumer product. By 1970, no self-respecting audiophile would own a cassette deck not sporting the Dolby logo. During that decade, Dolby forged the way into theater sound and, in 1982, introduced Dolby Surround. Ten years later, Batman Returns was the first film released in Dolby Digital Surround.

Speed (1994) marked Dolby's 18th straight Academy Award for Best Achievement in Sound. It was also the first Dolby Digital film to win the award. One year earlier, however, a contender for the digital surround market entered the ring. In 1993, dts was introduced via Steven Spielberg's blockbuster, Jurassic Park. Five years later, all five Best Picture and Best Sound nominees were released in dts and Saving Private Ryan, a Spielberg dts release, won for Best Sound.

Considering the fact that the total number of movies released worldwide in Dolby Digital last year was 703 and dts releases totaled 242, this is no small feat.

Needless to say, the Jurassic Park co-venture proved to be a tremendous success. In fact, the dts experience was so successful that both Spielberg and MCA/Universal Studios immediately invested in Digital Theater Systems, and have since committed all of their major film productions to dts surround.

However, Universal and Spielberg (along with every other DVD-Video maker) are also releasing their films in Dolby Digital. Dolby placed itself at the forefront of the DVD landscape from the earliest stages of the format's evolution. As a result, in 1995, Dolby Digital (AC-3) was made a mandatory audio format for NTSC countries and an optional format elsewhere. Dolby Digital 5.1 and dts are optional formats worldwide.

THE COMPRESSION THAT I GET

Both Dolby Digital 5.1 and dts are six-channel surround sound systems. Both encode six discrete channels of audio into blocks of information that are played back in left, right, and center front channels, two rear, and one optional sub-woofer (the .1 in 5.1). The digital audio coding used on CDs (16-bit PCM) yields a total dynamic range of 96dB from the loudest sound to the noise floor. This is achieved by taking 16-bit samples 44,100 times per second for each channel, which is often too much data to store or transmit economically, especially when multiple audio channels are desired. This makes some form of compression essential in order to deliver multichannel audio. However, as Michael DiCosimo, vice president of Dolby's East Coast Division, describes it, "Compressed is a pejorative term. People think of compressed as MP3, but we think more in terms of data reduction."

Compression is where the differences between Dolby's version of surround and dts' surround begin. Dolby Digital and dts save space by transmitting only the data that is necessary to portray the original sound, in essence throwing away the rest. Dolby compresses these 5.1 channels of digital audio down to a data rate of 448kbps. With a data rate of approximately 1.5mbps and a much lower compression ratio, dts employs less data compression--about 4:1 compared to Dolby Digital's variable 10-12:1. The higher dts data rate means potentially higher quality audio, particulady in dynamic range and signal-to-noise measurements. Dolby Theater Systems (dts) also claims effective 20-bit resolution for each of the six channels (much better than CD standards allow). According to dts' director of marketing, David DelGrosso, "It is a matter of sonic perfection vs. space consumption."