![]() ![]() In SP mode, the tape moves past the head at 1.31 linear inches per second (33.35 mmps). The head is rotating at 1,800 revolutions per minute (rpm), or 30 revolutions per second. The relationship between the tape and the rotating head drum is shown in this figure: Usually, this is not necessary, but if a tape is badly worn or stretched you may have to adjust the tracking. When you play with the "tracking" control on your VCR, what you are doing is adjusting the skew between the control track and the actual head position on the tape. It gets the heads lined up with the bands during playback.It tells the VCR how quickly to pull the tape past the drum (since the tape may stretch or shrink over time).It tells the VCR whether the tape was recorded in SP (standard play), LP (long play) or EP (extended play) mode.The control track is especially important: The yellow tracks represent the audio and control tracks. Since the drum contains two heads on opposite sides of the drum (180 degrees apart), the two heads alternate, each one reading or writing every other band. In this figure, the light blue bands are individual fields laid down by the recording head of the rotating head drum. Therefore, the data recorded on the tape looks like this: Each pass of the VCR's rotating head reads or writes the data for one field (262.5 scan lines) of the television image. A television image is divided into a series of 525 horizontal scan lines, half of which are displayed every 60th of a second. To solve this problem, two recording heads are mounted on a rotating drum that is tilted with respect to the tape. The tape would have to be moving past the head at a rate of many feet per second. A video signal contains perhaps 500 times more information than a sound signal, so the same approach cannot work. The tape might move past the head at a speed of 2 or 3 inches (5 - 8 cm) per second. That is, the tape moves past the recording head and the sound information is laid down as a long line following the length of the tape. In sound recording, the sound information is stored linearly on the tape. ![]() It must read the signals off the tape and convert them to signals that a TV can understand.īoth of these are formidable tasks, and the second one was a big technological challenge.It must deal with the tape - an extremely thin, fairly fragile and incredibly long piece of plastic. ![]()
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