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Introducing Dolby Multi-channel Audio Formats for Surround Sound Dolby Laboratories introduced the first surround sound format - Dolby Surround - in 1976, as an analog cinema sound format for use on 35mm film. Later in the early 1980s, this first multi-channel surround format became available on consumer gear. Since then, the lineup of Dolby sound formats has grown to a point that it has become increasingly difficult for the end customer to follow suit. As you will soon discover in this guide, to-day's discrete digital surround sound formats are a far cry from the first four-channel matrix-encoded analog Dolby Surround; their ability to reproduce a wide yet enveloping soundfield, intelligible dialog and pin-point localization of sounds, is far superior than ever.
Dolby Sound - Digital Audio formats for Playback We start our discussion by looking at the mainstream Dolby sound formats for multi-channel audio playback, namely, Dolby Surround, Dolby Digital, Dolby Digital Live, Dolby Digital EX, and Dolby Digital Surround EX.
Dolby Surround/Pro Logic is a Matrix-based technology. When a Dolby Surround soundtrack is created, four channels of sound are matrix-encoded into a two-channel sound track (ordinary stereo), by using phase shift techniques. The Pro Logic decoder extracts the four channels from the stereo sound; systems lacking the decoder will simply play back the audio as standard Stereo.Dolby Surround is the consumer version of the original multi-channel analog-optical film Dolby sound technology - Dolby Analog and Dolby Spectral recoding; it is still included today on nearly all 35mm film prints to serve as a backup in cinemas in case of problems with the digital soundtrack.Dolby Spectral Recording (Dolby SR) is a noise reduction technology used in almost all modern professional audio analog recordings. When used with Dolby Analog, Dolby SR helps improve the dynamic range of the analog recording by increasing the range - by as much as 25 dB - between peak level and noise floor.The introduction of the Dolby Digital multi-channel film sound format has eventually replaced Dolby Surround as the preferred technology to deliver surround sound via DVD-Video, digital television, and games. Interesting to note that though Dolby Surround was introduced as an analogue format, all Dolby Digital decoders include a digitally implemented Dolby Surround Pro Logic decoder for digital stereo signals that carry this matrix-encoded Dolby Surround sound format.
While the sound quality associated with Dolby Digital is not up to the same standard as the high resolution formats of DVD-Audio, SACD and the latest ultra-HD audio formats from both Dolby and DTS, yet its efficient coding structure is still capable of delivering high-quality discrete multi-channel audio that is more than adequate for movie applications. It is thanks to its efficient coding that Dolby Digital has become the 'quasi' de facto surround sound standard for the DVD world - it is capable of delivering quality audio without compromising on available DVD storage space for quality video content. Note: Dolby Digital is a flexible surround sound format. More specifically, it is an audio encoding scheme that supports up to 5.1 channels, but not all Dolby Digital soundtracks have 5.1 channels of audio; those that are, carry the designation 'Dolby Digital 5.1. For example, Dolby Digital 2.0 soundtracks (stereo or Dolby Surround Pro Logic) are compulsory on all Region 1 (U.S. and Canada) DVDs.
This extra 'Center Back' channel is in reality matrixed over the two left and right surrounds, rather than discrete. This is somewhat different from the design philosophy adopted in its extended DTS counterpart where this extra channel is discrete. This also explains why DTS ES can provide a more precise location for the rear-effects soundstage than the Dolby EX format. This extended surround Dolby sound format was originally developed by Lucasfilm THX and Dolby Laboratories under the brand name THX Surround EX. It is the home theater version of the 'Dolby Digital Surround EX'. Later, Dolby Laboratories began to license the THX Surround EX format under its own name as Dolby Digital EX for consumer home equipment. In other words, THX Surround EX and Dolby Digital EX are equivalent. To enjoy Dolby Digital EX, you need a home theater receiver or preamp/processor with Dolby Digital EX decoding and a speaker setup that supports 6.1 or 7.1 audio playback. In the case of a 7.1 speaker setup, the two back surround channels in this Dolby Sound format will be actually playing the same identical sound (ref. to picture below).
Dolby Digital EX encoded content is fully backward compatible with the standard 5.1-channel Dolby Digital playback systems in that no real sonic information is lost though the added realism provided by the sixth channel is would be missing from the overall listening experience.
Current Dolby Digital Surround EX soundtracks contain a digital
flag that can automatically activate the EX decoding in a
Home Theater receiver. For titles released prior to late
2001, however, you need to turn on the EX decoding manually.
Next: Dolby Digital High Definition Audio ...back to Dolby Sound Formats Sec. Index
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