【英语时差8,16】录像机如何记录（上）
时间：2019-03-06 作者：英语课 分类：英语时差8，16
英语课
Although audio tapes and video tapes look different, they’re based on the same principles. Each has a roll of magnetic material which slides past the so-called “playback head” in the VCR or cassette deck (cassette decks have one playback head, VCRs have two or more). In both machines, these heads detect changes in magnetism 1 as the tape moves by. The changing magnetic signal is translated into music on your tape deck, or both video and sound on your VCR. Without a changing magnetic signal over a playback head, you’d get no sound, no picture.