DTS Coherent Acoustics
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DTS Coherent Acoustics is the full name for the audio format standard usually known as just DTS. It is covered in U.S. Patent 5,956,674.
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[edit] Overview
DTS can transport audio up to 8 audio channels at up to a 192kHz sampling rate. It can be transported over S/PDIF, or can be encapsulated in wave files, DVDs and stored on CDDAs. DTS codecs exist for desktop computers as well as being embedded into many home cinema AV receivers. The format offers variable compression ratios, targeting a wide variety of bit rates, although the most often used compression ratio for DVD and cinema audio is about 1:4, resulting in a fairly high bitrate. DTS also includes several low-bitrate hacks, such as joint frequency encoding, that are generally frowned upon in this context, and should not be encountered on high quality DTS source material.
The base specification allows for 5.1 channels of audio with a 48kHz sampling rate. Further specification extensions allow for an additional 2 channels and/or additional high frequency data to be transmitted. It encodes audio by splitting it into 32 subbands, each with a bandwidth of 750 Hz, which are then encoded using ADPCM. There are 4 ADPCM coefficients, which are processed with vector quantization for transmission (there is a 4,096-entry codebook). The residual (prediction error) is quantized either linearly (using a variable number of bits), or using VQ, depending on the bit allocation to the subband - a global bit allocation scheme allocates bits to each subband. Data bits may also be entropy encoded.
Due to fewer calculations involved in higher bitrates, DTS encoding is particularly fast and CPU-easy compared to Dolby Digital. Real-time DTS encoding is also inherently low-latency compared to the 130ms of Dolby Digital, making it much more suitable for interactive (real-time) applications, such as video games. Several Playstation 2 games have offered DTS 5.1 surround output, in addition to stereo Pro-logic encoded PCM. DTS 5.1 output is also offered on several models of HD DVD players, where the player converts an original soundtrack (of Dolby Digital +, Dolby True-HD, or multi-channel LPCM) into a DTS 5.1 bitstream.
Theatrical DTS uses a different codec, called APT-X 100.[1] Home-theater receivers cannot be used with theatrical DTS programming, and vice versa.
The DTS Coherent Acoustics standard (ETSI 102 114 v1.2.1) is published by the ETSI.[2] This standard specifies an algorithm for the decoder. Also, a white paper is available from DTS Inc.[3] This white paper puts more accent on encoding the stream.
[edit] DTS in cinemas
DTS is used on film prints, where it competes with the Dolby Digital (AC-3) and SDDS standards.[4] It is used less often than Dolby Digital. Dolby Digital and SDDS tracks are printed onto the physical film medium, as their bit-rates allows them to fit in limited space. A DTS track, however, has a higher bitrate and therefore cannot be printed onto the film. Instead, a timecode is printed onto the film and the DTS soundtrack shipped to the cinema as a pair of CDs in addition to the film reels.[4] When the film is projected, the timecode is read from the film and the equivalent sound comes from the DTS CD-decoding equipment.[4]
It is argued that in a cinema environment DTS produces higher-fidelity sound than DD encoded film, and greater robustness in the event of damaged film, but the extra complication of using CDs is less convenient for the projectionist and they are more likely to be missing or damaged.
[edit] References
- ^ Tozer, Edwin Paul J. (2004). Broadcast Engineer's Reference Book. Focal Press. ISBN 0240519086.
- ^ ETSI Publications Download Area, search for DTS Coherent Acoustics
- ^ DTS Coherent Acoustics White Paper
- ^ a b c DTS Postproduction Guide
[edit] See also
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