How Your VCR holds a Note
VCR-盒式磁带录像机VCR是Video Cassette Recorder的缩写盒式磁带录像机。就功能上而言，它是使用空白录像带并加载录像机进行影像的录制及存储的监控系统设备。VCR作为许多晚会盛典的重要环节和收视利器,可以突破演出现场的局限、拓展真实的情感时空,能够承上启下、营造氛围和升华主题,起到独特的艺术效果。现在的VCR多指一个视频片断。
Ever wondered how VCRs function? Learn about them on this Moment of Science.
Although audio tapes(录音磁带) and video tapes(录像磁带) look different, they’re based on the same principles. Each has a roll of (1)magnetic material which slides past the so-called “playback head(放音磁头)” in the VCR or cassette deck(盒式磁带录音座) (cassette decks have one playback head, VCRs have two or more).
In both machines, these heads detect changes in magnetism as the tape moves by. The changing magnetic signal is translated into music on your tape deck(磁带卡座), or both video and sound on your VCR. Without a changing magnetic signal over a playback head, you’d get no sound, no picture.
But here’s a mystery: When you press pause on the VCR, the screen doesn’t go blank. Instead, you get a frozen image. Remember, you need a changing magnetic signal to create even a still video image. If the video tape isn’t moving, where is this changing signal coming from?
We’re used to VCRs doing this, but it’s actually kind of strange. It would be like (2)pressing pause on a cassette deck and having the sound remain in your (3)speakers, Pavarotti(帕瓦罗蒂（意大利男高音歌唱家）) holding his high C until you press play again. VCRs do this trick by moving both the tape, AND the playback heads, which spin rapidly past the tape as it moves through the machine.
Pausing a video tape does indeed stop the tape, but it doesn’t stop the spinning playback heads. These continue to swipe past the stationary tape, detecting enough of a magnetic signal for one still frame of video. Modern, hi-fi VCRs(高保真录像机) automatically mute the sound when they are paused, so you don’t get a sustained audio sound as well!
Notes:
(1)magnetic [m?ɡ'netik] adj.地磁的；有磁性的；有吸引力的
Earth was once magnetic only, and shall return to a magnetic only energy flow.
地球曾经是单一磁性的，并将返回到单一磁性的能量流。
(2)pressing ['presi?] 紧迫的；迫切的；恳切的
Increasing or reducing displayed value by pressing button or .
按下或按钮可使显示数值增加或减少。
(3)speakersn. 扬声器;发言者（speaker的复数）;演说家
Speakers using reflectors to widen the dispersion are not new.
发言者使用反射来扩大分散并不是新的。 |