On some discs we even have the option of raw PCM with no compression at all. Each company has developed a line-up of brand new sound formats to go with the new disc types, using advanced forms of audio compression to deliver high quality to the home listener, quality sometimes matching that of the studio master itself. Jumping into the fray once more are Dolby and DTS. When there's so much more disc space available on an HD DVD or a Blu-ray, why should we be limited to the heavily-compressed sound formats we got on DVD? High Definition video deserves High Definition audio to go with it. Along with that has come an expectation for an attendant boost in audio quality. The advent of Blu-ray and HD DVD has brought a dramatic increase in picture quality from Standard Definition to High Definition. Dolby uses more efficient compression techniques than DTS and can usually achieve results at 448 kb/s comparable to DTS at 754 kb/s. While a 448 kb/s Dolby track is better than a 384 kb/s Dolby track, a 754 kb/s DTS track is not necessarily better than a 448 kb/s Dolby track just because the number is larger. Also note that Dolby and DTS use entirely different compression techniques, and their bit rate numbers are not directly comparable to one another. However, it also means that the audio track takes up more disc space, which can eat into the bit rate allocated to video quality. Within each format, the higher the bit rate means the less compression needed and the less data removed from the master. DTS has two bit rate encoding options: the commonly used 754 kb/s or a rarely offered high rate of 1.5 Mb/s. Standard Dolby Digital can be encoded in a variety of bit rates, the most common being 192 kb/s (reserved for 1.0 or 2.0 soundtracks and generally poor fidelity), 384 kb/s (OK quality), and the maximum 448 kb/s (used on the majority of DVD 5.1 soundtracks). But if done poorly or over-compressed, the audio may lose fidelity. If done properly, the end result should sound seamless to the listener. In theory, the data removed should consist mainly of either frequencies beyond the range of human hearing or frequencies that would normally be masked by other frequencies in the track anyway. Before making it to disc, each format selectively filters out data from the studio's digital audio master using perceptual encoding techniques. The reality of the situation is that both Dolby Digital and DTS are capable of delivering very good, sometimes even exceptional sound quality on DVD.īoth Dolby Digital and DTS are "lossy" compression codecs. Sometimes that's true and sometimes not, but that's a discussion topic for another day. Though it hasn't always panned out that way in actual practice, there is a perception in the DVD marketplace that DTS is the "better" sound option that will provide greater fidelity to the source. DTS is optional, and is generally considered (fairly or not) an added-value feature. The DVD spec requires all discs to contain either a Dolby Digital or PCM soundtrack as the base standard (pretty much everyone uses Dolby), and all DVD players are required to decode both. A small number of discs (mostly music concerts) may provide 2-channel PCM audio, but those are few and far between. Both can accommodate movie soundtracks from monaural 1.0 to multi-channel 5.1, and in some cases add a matrixed center back channel as well (DTS also offers a discrete 6.1 option on selected titles). On Standard-Def DVD, there are essentially only two competing sound formats to choose from: Dolby Digital or DTS. It doesn't help that the companies who designed these sound formats (Dolby and DTS) haven't always been clear in their labeling or naming conventions. It seems that most early adopters can easily identify the benefit of a High Definition picture over Standard-Def DVD, but making sense of the difference between Dolby Digital Plus and DTS-HD, or PCM and TrueHD is a lot harder to get a good grasp on. If there's one request we get here at High-Def Digest more than any other, it's to help readers sort through all the confusion swirling around the new audio formats that come on HD DVD and Blu-ray discs. This week: Josh provides a comprehensive rundown of all the audio formats currently available on next-gen disc. Editor's Note: As part of his twice-monthly column here at High-Def Digest, from time to time, Josh Zyber answers frequently asked questions related to High-Definition and both Blu-ray on HD DVD.
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