Dolby Surround

Dolby Surround is an analog multi-channel sound system in the home that houses with the help of a matrix encoding four channels of sound in two audio tracks. When playing back four channels are decoded from the two channels again. Dolby Surround is technically related to the use in the cinema Dolby Stereo.

The Dolby Surround was developed by Dolby Laboratories Inc. and licensed.


A Dolby surround sound system consists of an amplifier with decoder and speakers for: front left, front right, center signal ( center ), and a surround channel, the latter is often operated with two speakers, but receive the same signal. A LFE ( subwoofer ) is provided not directly, but is generated in conventional reproduction equipment from the existing signal with a crossover ( low pass).

( Called center, mounted in the cinema behind the screen ) The central channel is detected from those signal components that are represented coherent in phase on both channels, while the effects channel (Surround / Rear ) is encoded by a phase shift of 180 ° and so the decoder can be detected. In addition, the surround channel is available only in a limited frequency range so as to avoid distortions of the signal transmission in the higher frequency ranges. All uncorrelated Shares are developed on one of Dolby Laboratories, so-called "adaptive array " either the left, the right or the FX channel in the decoding assigned. The adaptive matrix has the task to identify and nachzusteuern a directional preference from the stereo signal. A clean channel separation is inherently impossible and is only simulated.


Dolby Surround is backward compatible to stereo, that is, you can easily play back a Dolby Surround signal on each stereo device. A certain spatial effect arises here by the phase shift by itself, the surround sound signal seems partly to come from behind, even if there is no speaker ( this is called excess width of the stereo signal ). In the case of a mono playback, the surround sound signal extinguishes itself. The matrix signal is after sonic processing, such as an equalizer, still decodable.


Dolby Surround has declined in importance in the digital video sector, with new storage media such as DVD's have digital, discrete channel formats such as Dolby Digital and DTS partially displaced analog formats. On VHS tapes and especially on audio CDs, where due to the system Dolby Digital and DTS can not be used, Dolby Surround is, however, still used a lot. Most important argument for the use of the backward compatibility with all existing stereo or even mono playback systems, while Dolby Digital or DTS decoder own need.

The improved matrix Dolby Surround Prologic has been further developed. With Dolby Prologic II is available today in many home theater amplifiers, a mode in which the specific disadvantages of the old Surround Prologic are to be overcome: Approximately one did not bind limited, stereophonic Rear signal is generated there, as well as the effect of the center - filter adjusted be.