Digital Theater System
From Wikipedia, the free encyclopedia
DTS (also known as Digital Theater Systems), owned by DTS, Inc. (NASDAQ: DTSI), is a multi-channel digital surround sound format used for both commercial/theatrical and consumer grade applications (with significant technical differences between home and commercial/theatrical variants: the latter being a traditional ADPCM compression system and the former a sophisticated hybrid perceptual and signal-redundancy compressor based on ADPCM called APTX-100). It is used for in-movie sound both on film and on DVD, and during the last few years of the format's existence, several Laserdisc releases had DTS soundtracks.
Contents |
[edit] History
One of the company's initial investors was film director Steven Spielberg, who felt that theatrical sound formats up until the company's founding were no longer state of the art, and as a result were no longer optimal for use on projects where quality sound reproduction was of the utmost importance. Work on the format started in 1991, four years after Dolby Labs started work on their new codec, Dolby Digital. The basic and most common version of the format is a 5.1 channel system, supporting five primary speakers and a subwoofer, referred to as an LFE (Low Frequency Effects) channel. Note however that encoders and decoders support numerous channel combinations and stereo, four-channel and four-channel+LFE soundtracks have been released commercially on DVD, CD and LaserDisc.
Other newer DTS variants are also currently available, including versions that support up to 7 primary audio channels plus 1 LFE channel (DTS-ES). DTS's main competitors in multichannel theatrical audio are Dolby Digital and SDDS, although only Dolby Digital and DTS are used on DVDs and implemented in home theater hardware. Spielberg debuted the format with his 1993 production of Jurassic Park, which came slightly less than a full year after the official theatrical debut of Dolby Digital (Batman Returns). In addition, Jurassic Park also became the first home video release to contain DTS sound when it was released on Laserdisc in January 1997, two years after the first Dolby Digital home video release (Clear and Present Danger on LaserDisc) which debuted in January of 1995.
In theatrical use, information in the form of a modified time code is optically imaged onto the film. An optical LED reader reads the timecode data off the film and sends it to the DTS processor which uses this timecode to synchronize the projected image with the soundtrack audio. The actual audio is recorded in compressed form on standard CD-ROM media at a bitrate of 1103 kbit/s. The processor also acts as a transport mechanism, as it holds and reads the audio discs. Newer units can generally hold 3 discs, allowing a single processor/transport to handle 2-disc film soundtracks along with a 3rd disc containing sound for theatrical trailers. In addition, specific elements of the imprinted timecode allow identifying data to be embedded within the code, ensuring that a certain film's soundtrack will only run with that film.
DTS and Dolby Digital (AC-3), DTS's chief competitor in the cinema and home-theater market, are often compared due to their similiarity in product goals. In theatrical installations, DTS can deliver better audio fidelity (due to the higher data-rate afforded by CD-ROM media.) AC-3 audio is placed between sprocket holes, leaving the audio content susceptible to physical damage due to film aging and mishandling. However, AC-3 (and SDDS), are stored entirely on the 35mm film itself, and do not require delivery of separate CD-ROM discs to theaters, simplifying distribution. Disregarding the CD-ROM as a potential point of failure in a cinema audio system, the CD-ROM media is not damaged/degraded by repeated screenings, and rarely require replacement during the theatrical run of a given movie title.
In the consumer (home-theater) market, AC-3 and DTS are closer in terms of audio performance. When the DTS audiotrack is encoded at its highest legal bitrate (1.5MBps), most technical experts regard DTS as achieving perceptual transparency (i.e. indistinguishable to the uncoded-source in a double-blind test.) At AC-3's maximum bitrate of 640Kbps, Dolby claims similar transparency. However, the DVD format limits AC-3 audiotracks to 448Kbps, and some publishers limit the AC-3 bitrate further (to 384Kbps.) Even at 448Kbps, (DVD) AC-3 operates at a higher bitrate than theatrical (35mm movie) AC-3, therefore a properly-equipped home-theater already achieves surround sound superior to a cinema AC-3 installation. Likewise, DTS-audio on movie DVDs is commonly encoded at a reduced bitrate, allowing a single title to fit multiple 5.1 soundtracks (AC-3 + DTS.) At this reduced rate (769Kbps), DTS no longer retains audio-transparency.
It should be noted, that AC-3 and DTS use different coding tools and syntax to perceptually compress audio, and therefore, the raw bitrates of the two formats do not indicate an objective measure of sound-quality. Regardless, DTS proponents claim that the extra bits give higher fidelity and more dynamic range, providing a richer and more life-like sound. They also say that DTS is louder with less hiss, even at the same relative volume.
[edit] DTS as a codec
DTS is an enhanced copy of a French patent called LC Concept, first used in 1990 for the movie Cyrano de Bergerac.
On the consumer level, DTS is the oft-used shorthand for the DTS Coherent Acoustics codec, transportable through S/PDIF and used on DVDs, CDDAs, LDs and in wave files. This system is the consumer version of the DTS standard, using a similar codec without needing separate DTS CD-ROM media.
[edit] DTS playback
Both music and movie DVDs allow delivery of DTS-audiotracks. But DTS was not part of the original DVD specification (1997), so early DVD-players did not recognize DTS-audiotracks at all. The DVD specification was revised to allow optional inclusion of DTS-audiotracks. The DVD-title must carry 1 (or more) primary audiotrack of AC-3, MPEG-1, or LPCM format. The DTS-audiotrack, if present, can be selected by the user. Modern DVD-players generally rely on an external audio-receiver to decode DTS audiotracks. (DVD-players with integrated AC-3/DTS 5.1 decoders were built and sold in limited quantity.) Nearly all standalone-audio receivers and many integrated (home theater in a box) DVD-player/receivers can decode DTS (in addition to AC-3.)
For PC playback, many software players support the decoding of DTS. The VideoLAN project has created a decoding module for DTS called libdca (formerly libdts), which is the first open source implementation of DTS.
[edit] DTS variants
In addition to the standard 5.1 channel DTS Surround codec, the company has several other technologies in its product range designed to compete with similar systems from Dolby Labs. The primary new technologies are:
- DTS-ES (DTS Extended Surround) - includes two variants, DTS-ES Matrix and DTS-ES Discrete 6.1, depending on how the sound was originally mastered and stored.[1] DTS-ES Discrete provides 6.1 discrete channels, with a discretely recorded (non-matrixed) back surround channel; in home theater systems with a 7.1 configuration, the two rear-center speakers play in mono. DTS-ES Matrix provides 5.1 discrete channels with a matrixed back surround audio channel. DTS-ES commonly works on a Matrix system, whereby processors that are compatible with the ES codec look for and recognize "flags" built into the audio coding and "un-fold" the rear-center sound from data that would otherwise be sent to rear surround speakers. This is notated as DTS-ES 5.1. Less frequently, DTS-ES data can be encoded with a Discrete 6th audio channel (the rear-center), meaning that the audio data for the 6th channel is stored separately from the other information, and is not embedded or matrixed among other channels. This is notated as DTS-ES 6.1, as the center rear is completely discrete from the other channels. ES capable processors can recognize the discrete 6th channel, and play it back if connected to the necessary speaker(s). In contrast, Dolby's competing EX codec, which also boasts a center rear channel, can only handle matrixed data and does not support a discrete 6th channel. DTS-ES is backward compatible with standard DTS setups, so non-ES equipment which does not recognize the flags or with ES enabled equipment that lack the extra speaker connections, sound plays back in 5.1 as if it were standard DTS. Only a few DVD titles have been released with DTS-ES Discrete.
- DTS NEO:6 - Neo:6, like Dolby's Pro-Logic IIx system, can take stereo content and convert the sound into 5.1 or 6.1 channel format.
- DTS 96/24 - Allows the delivery of 5.1 channels of 24-bit, 96 kHz audio and high quality video on the DVD-Video format. Prior to the invention of DTS 96/24, it was only possible to deliver two channels of 24-bit, 96 kHz audio on DVD-Video. DTS 96/24 can also be placed in the video zone on DVD-Audio discs, making these discs playable on all existing DVD players.
- DTS-HD Master Audio - Previously known as DTS++ and DTS-HD, DTS-HD Master Audio supports a virtually unlimited number of surround sound channels, can downmix to 5.1- and two-channel, and can deliver audio quality at bit rates extending from DTS Digital Surround up to lossless. DTS-HD Master Audio is selected as an optional surround sound format for Blu-ray and HD-DVD. DTS-HD Master Audio and Dolby TrueHD are the only technologies that deliver compressed lossless surround sound for these new disc formats, ensuring the highest quality audio performance available in the new standards. (n.b. DTS Coherent Acoustics coding system has been selected as mandatory audio technology for both the Blu-ray Disc (BD) and High Definition Digital Versatile Disc (HD-DVD) - [2])
- DTS Connect - This is a function pack available on the computer platform only. It is found on soundcards with CMedia CMI8788/CMI8770 Soundcontroller.
- DTS Interactive This is a realtime DTS stream encoder. It is a part of DTS Connect, or can found on stand alone devices (e.g. Surround Encoder, HD DVD / BluRay Player)
- DTS Virtual - A relatively new development. Intended for use in conjunction with a Dolby Headphone processor. It allows a virtual (as the name suggests) 5.1 surround sound to be heard through a standard pair of headphones. It provides a better spatial awareness than Dolby Headphone on its own (which is primarily intended to provide a surround sound effect from standard stereo sources).
