Digital Theater System

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. It is used for in-movie sound both on film and on DVD, and during the last few years of the Laserdisc format's existence, several releases had DTS soundtracks.

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 its new codec, Dolby Digital. The basic and most common version of the format is a 5.1 channel system, similar to a Dolby Digital setup, which encodes the audio as five primary (full-range) channels plus a special LFE (low-frequency effect) channel, for the subwoofer.

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 seven primary audio channels plus one 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 1,103 kbit/s. The processor also acts as a transport mechanism, as it holds and reads the audio discs. Newer units can generally hold three discs, allowing a single processor/transport to handle two-disc film soundtracks along with a third 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 provided the Digital Audio for IMAX until 2001, when Dolby took over.

DTS and Dolby Digital (AC-3), DTS's chief competitor in the cinema and home theater market, are often compared due to their similarity in product goals. In theatrical installations, AC-3 audio is placed between sprocket holes, leaving the audio content susceptible to physical damage due to film wear and mishandling. DTS audio is stored on a separate set of CD-ROM media, whose greater storage capacity affords the potential to deliver better audio fidelity. However, the separation of print film and audiotrack is both a blessing and a curse. AC-3 (and SDDS) reside entirely on the 35 mm film itself, simplifying distribution by eliminating an extra (optional) deliverable. But DTS's CD-ROM media is not subject to the usual wear and damage suffered by the film print during the normal course of the movie's theatrical screening. Disregarding the separate CD-ROM assembly as a potential point of failure, the DTS audiopath is comparatively impervious to film degradation, excepting that the film-printed timecode is completely destroyed.

In the consumer (home theater) market, AC-3 and DTS are close in terms of audio performance. When the DTS audio track is encoded at its highest legal bitrate (1,536 kbit/s), technical experts rank DTS as perceptually transparent for most audio program material (i.e., indistinguishable to the uncoded source in a double blind test.) Dolby claims its competing AC-3 codec achieves similar transparency at its highest coded bitrate (640 kbit/s). However, in program material available to home consumers (DVD, broadcast and subscription Digital TV), neither AC-3 nor DTS run at its highest allowed bitrate. DVD and broadcast (ATSC) HDTV cap AC-3 bitrate at 448 kbit/s. But even at 448 kbit/s, consumer audio gear already enjoys better audio performance than theatrical (35 mm movie) installations, which are limited to even lower bitrates. When DTS-audio was introduced to the DVD specification, studios authored DVD-movies at DTS's full bitrate (1,536 kbit/s). Later movie titles were almost always encoded at a reduced bitrate of 768 kbit/s, ostensibly to increase the number of audio-tracks on the movie disc. At this reduced rate (768 kbit/s), DTS no longer retains audio transparency.

AC-3 and DTS are sometimes judged by their encoded bitrates. DTS proponents claim that the extra bits give higher fidelity and more dynamic range, providing a richer and more lifelike sound. But no conclusion can be drawn from their respective bitrates, as each codec relies on different coding tools and syntax to compress audio. When the DTS and AC-3 audiotracks on the same DVD are compared, some movies exhibit noticeable differences. A DTS track is often louder with less hiss, even at the same relative playback volume.

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 which received the best sound award at the César Awards in 1991.

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.

There are significant technical differences between commercial/theatrical and home variants: the former being a traditional ADPCM compression system and the latter a sophisticated hybrid perceptual and signal-redundancy compressor based on ADPCM called APTX-100.

DTS playback

Both music and movie DVDs allow delivery of DTS audio tracks. But DTS was not part of the original DVD specification (1997), so early DVD players did not recognize DTS audio tracks at all. The DVD specification was revised to allow optional inclusion of DTS audio tracks. The DVD title must carry one or more primary audio tracks in AC-3 or LPCM format (in Europe, MPEG-1 is also an allowed primary track format). The DTS audio track, if present, can be selected by the user. Modern DVD players can now decode DTS natively with no problem, or pass it through to an external decoder. Nearly all standalone receivers and many integrated ("home theater in a box") DVD player/receivers manufactured today can decode DTS.

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. The Sony Playstation 3 and Xbox 360 are capable of DTS decoding and output via Toslink or HDMI as LPCM. However on the 360, this feature is only found on new the Elite model and newer models available since. Only the Playstation 3 console has the ability to decode DTS-HD Master Audio or High Resolution since the newest firmware update, ver. 2.30 and up. The Xbox 360 can only output the core bitstream at 1.5 Mbit/s via LPCM or Toslink.

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 70 mm

This is a process designed specifically for playback in motion picture theaters equipped with 70mm projection and 6-track stereophonic surround sound. It is believed that this is the digital equivalent of the 70mm Dolby Stereo 6-Track analog mixing process. It works the same way that 35 mm DTS does, only the size of the print stock is bigger. The 6-track audio data is played on special compact discs in synchronization with the picture that is projected on a screen. The 6-track system plays on a properly organized 5.1 system: left, right, center, LFE speaker, and split surrounds.

DTS-ES

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. DTS-ES Discrete provides 6.1 discrete channels, with a discretely recorded (non-matrixed) center-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 center-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 sixth audio channel (the rear-center), meaning that the audio data for the sixth 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 sixth 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 sixth 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

DTS 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

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 DTS compatible DVD players.

DTS-HD High Resolution Audio

DTS-HD High Resolution Audio, like DTS-HD Master Audio, is an extension to the original DTS audio format. It delivers up to 7.1 channels of sound at 96 kHz sampling frequency and 24 bit depth resolution. DTS-HD High Resolution Audio is selected as an optional surround sound format for Blu-ray Disc and HD DVD with constant bit rates up to respectively 6.0 Mbit/s and 3.0 Mbit/s. It is supposed to be an alternative for DTS-HD Master Audio where disc space may not allow it.

DTS-HD Master Audio

DTS-HD Master Audio, previously known as DTS++ and DTS-HD, 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 (24-bit, 192 kHz). DTS-HD Master Audio is selected as an optional surround sound format for Blu-ray and HD DVD, where it has been limited to a maximum of 8 discrete channels. DTS-HD MA supports variable bit rates up to 24.5 Mbit/s on a Blu-ray Disc and up to 18.0 Mbit/s for HD-DVD, with 6 channel encoded at up to 192 kHz or 8 channels encoded at 96 kHz/24 bit. In case more than 6 channels are used, a "Channel Remapping" function allows for remixing the soundtrack to compensate for a different channel layout in the playback system compared to the original mix. Currently the Japanese version Pioneer BDP-LX80 supports bitstream digital output of the format along with the Samsung BD-P1400 (through a firmware update). All Blu-ray and HD DVD players can decode the DTS "core" resolution soundtrack at 1.5 Mbit/s, however. 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).

Others

- DTS Connect: This is a real-time encoding technology for interactive media available on the computer platform only. It converts any audio signals on a PC into the 5.1-channel DTS format and transports it via a single S/PDIF cable. It is found on soundcards with CMedia CMI8788/CMI8770 Soundcontroller and onboard audio with Realtek ALC883DTS/ALC889A/ALC888DD-GR and SoundMAX AD1988 chip.

- DTS Interactive: This is a realtime DTS stream encoder. It is a part of DTS Connect, and can be found on stand alone devices (e.g., Surround Encoder, HD DVD / Blu-ray Player). Nearly a dozen titles on the PlayStation 2 feature the "DTS Interactive" realtime stream encoder, such as Grand Theft Auto: Vice City, and Terminator 3: Rise of the Machines.

- DTS Surround Sensation: A relatively new development, previously known as DTS Virtual. It allows a virtual 5.1 surround sound to be heard through a standard pair of headphones.