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24/10/2011

digital television

 

Tonic train signaling compressed encoding  

 (1) sense of hearing masking effect. In person's sense of hearing, a sound's existence concealed another sound's existence, the masking effect was a more complex psychology and the physiological phenomenon, including person ear's frequency range masking effect and time domain masking effect.

  (2) person of ear to sound directional characteristic. Regarding the 2KHZ above high frequency sound signal, the person ear is very difficult to judge its directivity,dvb t tuners          thus stereo broadcast's high-frequency unit does not need to duplicate stores.  

 Internationally had once drawn up three kind of standards to the digital image code, mainly uses in TV conference's H.261, mainly uses in the stationary picture the JPEG standard, mainly uses in the continual image the MPEG standard.  

 Reduces staff the decoding standard aspect in the HDTV video frequency pressure, the US, Europe, Japan is equipped with the difference, has used the MPEG-2 standard. MPEG (Moving Picture Expert Group) the meaning is “the movement image expert group”, after the compression information may supply computer processing, may also carries on the assignment in existing and future visual broadcast channel.

  In the audio frequency code aspect, Europe, Japan have used the MPEG-2 standard; The US has accepted Dubi the company (Dolby) AC-3 plan, MPEG-2 is the alternative scheme.   Regarding China, the source arranges the decoding standard also to be able from now on with the US, Europe, Japan to use the MPEG-2 standard equally.   (3) digital television's multiplying system

Digital television multiplexing system is the key part of the HDTV. From the sender information flows, it will be video, audio, and other auxiliary data encoder data from the bit stream, the processing of compound into a single serial bit stream, for channel coding and modulation. The receiving end and the process is reversed.
  Analog television systems do not have multiplexer. In digital television, audio, video multiplexer, auxiliary data stream through a packer package (this is a popular saying, is actually a data packet ), and then combined into a single road. Current network communication data is transmitted according to a certain format package. HDTV data package will enable it to have the scalability, hierarchical,dvb t receivers interactive basis.

Pay TV is now and the future development direction of the tv. Multiplexer for packetized program information of scrambling, make its randomization, the receiver has a key to descramble.

In HDTV multiplexing transmission standards, the United States, Europe, Japan also no differences, adopt MPEG-2 standard. The United States has MPEG-2 demultiplexing chip. Our country will probably be using MPEG-2 as the multiplexing transmission standard.

HDTV packet length is 188 bytes, it was ATM cell integer times. Next to the optical fiber as transmission medium, taking ATM as the information transfer mode broadband integrated services digital network is likely to become the next" information freeway" main facilities. Uses 4 ATM cell to complete transmission of a HDTV packets, which can be up to HDTV and ATM convenient interface.

( 4) the digital television channel coding and modulation and demodulation
  Digital TV channel coding and modulation and demodulation was designed by error correction coding, coding, equilibrium, grid technology to improve the signal anti-interference ability, through the modulation of the transmitted signals are placed on the carrier or burst,cable supplier  preparing for launch.

We present the national digital TV formats, standards are not unified, mainly refers to the various countries in the aspects of the different, specific include error correction, equalization technology is different, different bandwidth, especially the different modulation modes.