HDTV Standards
In North American countries, high definition television standards are defined and regulated by the Advanced Television Systems Committee. A high definition television sold in North America must comply with such standards. The standards govern aspects such as transmission, video and audio. All high-definition televisions must have a video display in 16 to nine aspect ratio.
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Terminology
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The ATSC uses a set of technical words when referring to the various aspects of high-definition television. The number of active lines is a measure of the television screen's vertical resolution; the number of H-samples is a measure of the screen's horizontal resolution. The frame rate refers to the rate at which an image is refreshed. A frame rate may either be progressive, where the lines of each frame are drawn in order, or interlaced, where the lines of each frame are drawn alternately.
Video Standards
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The ATSC supports two separate standards for HDTV video quality. The first, called HDTV format A, supports 720 active lines and 1280 active H-samples. Format A has a progressive frame rate of 60 or 30 frames per second. HDTV format B, on the other hand, supports 1080 active lines and 1920 active H-samples. Frame rates may be either progressive or interlaced at 30 frames per second.
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Audio Standards
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A total of seven service types of audio transmission are regulated by the ATSC. These consist of Complete Main, Music and Effect, Visually Impaired, Hearing Impaired, Dialogue, Commentary and Emergency and Voice-Over. All service types except for CM and ME are broadcast on a single channel at a 128 Kb per second bit rate. CE and ME have from one to 5.1 channels, and are compressed from 64 to 384 Kb per second.
Transmission Standards
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A range of transmission standards are regulated by the ATSC, and the specific active nominal bit rate, or the transmission speed, depends on the video standard of the high-definition television. Format A with a frame rate of 30 Hz is transmitted at a bit rate of 1485 Mb per second, and a frame rate of 60 frames per second is transmitted at 1485 Mb per second. For format B, all frame rates are transmitted at 1485 Mb per second.
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References
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