Dolby Surround
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Dolby Surround is an analog multi-channel sound system in the home that uses matrix coding to accommodate four sound channels in two sound tracks. When playing, four channels are decoded from the two channels. Dolby Surround is technically related to Dolby Stereo used in the cinema .
The Dolby Surround process was developed and licensed by Dolby Laboratories Inc.
construction
A Dolby Surround system consists of an amplifier with a decoder and loudspeakers for: front left, front right, middle signal (center) and a surround sound channel, the latter is often operated with two loudspeakers, but they receive the same signal. An LFE channel (subwoofer) is not provided directly, but in conventional playback systems it is generated from the existing signal by means of a crossover (low pass).
The middle channel (called the center, located behind the screen in the cinema) is recognized from those signal components that are represented phase-coherently on both channels, while the effect channel (surround / rear) is coded by means of a phase shift of 180 ° and so by the decoder can be recognized. In addition, the surround sound channel can only be used in a limited frequency range in order to avoid alienation of the signal transmission in higher frequency ranges. All uncorrelated components are assigned to either the left, the right or the effects channel during decoding using a so-called “adaptive matrix” developed by Dolby Laboratories. The adaptive matrix has the task of recognizing a directional preference from the stereo signal and adjusting it accordingly. A clean channel separation is not possible due to the principle and is only simulated.
compatibility
Dolby Surround is backwards compatible with stereo ; H. you can easily reproduce a Dolby Surround signal on any stereo device. A certain surround sound effect occurs by itself due to the phase shift, the surround sound signal seems to come partially from behind, even if there is no loudspeaker at all (this is referred to as excessive width of the stereo signal). In the case of mono playback, the surround sound signal cancels itself out. The matrix signal can still be decoded after sound processing, for example an equalizer .
development
Dolby Surround has lost in importance in the digital video sector. Storage media such as DVD have replaced digital, channel-discrete formats such as Dolby Digital and DTS in some cases . On VHS cassettes and especially on audio CDs, where Dolby Digital and DTS cannot be used due to the system, Dolby Surround is still widely used today. The most important argument for its use is the downward compatibility with all existing stereo and even mono playback systems, while Dolby Digital or DTS require their own decoders.
The improved matrix process Dolby Surround Prologic has been further developed. With Dolby Prologic II there is now an operating mode in many home theater amplifiers in which the specific disadvantages of the old Surround Prologic are to be overcome: For example, a non-band-limited, stereophonic rear signal is generated there, and the effect of the center filter can also be adjusted become.
See also
literature
- Thomas Görne: Sound engineering. 1st edition, Carl Hanser Verlag, Leipzig, 2006, ISBN 3-446-40198-9
- R. Beckmann: Manual of PA technology, basic component practice. 2nd edition, Elektor-Verlag, Aachen, 1990, ISBN 3-921608-66-X
