首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Modern technology may not have improved the world all that much but it certainly has made life noisier. Unmuffled motorcycles, b
Modern technology may not have improved the world all that much but it certainly has made life noisier. Unmuffled motorcycles, b
admin
2013-11-29
46
问题
Modern technology may not have improved the world all that much but it certainly has made life noisier. Unmuffled motorcycles, blaring car alarms, and roving boom boxes come first, second, and third on my list of most obnoxious noise offenders, but everyone could come up with his own version of aural hell—if he could just find a quiet spot to ponder the matter.
Yet what technology has done, other technology is now starting to undo, using computer power, to zap those ear-splitting noises into silence. Previously silence-seekers had little recourse except to stay inside, close the windows, and plug their ears. Remedies like these are quaintly termed "passive" systems, because they place physical barriers against the unwanted sound. Now computer technology is producing a far more effective "active" system, which doesn’t just contain, deflect, or mask the noise, but annihilates it electronically.
The system works by countering the offending noise with "anti-noise", a somewhat sinister-sounding term that calls to mind antimatter, black holes, and other Popular Science mindbenders but that actually refers to something quite simple. Just as a wave on a pond is flattened when it merges with a trough that is its exact opposite (or mirror image) , so can a sound wave be negated by meeting its opposite.
This general theory of sound cancellation has been around since the 1930s. In the fifties and sixties it made for a kind of magic trick among laboratory acousticians playing around with the first clunky mainframe computers. The advent of low-cost high-power microprocessors has made active noise-cancellation systems a commercial possibility, and a handful of small electronics firms in the United States and abroad are bringing the first ones onto the silence market.
Silence buffs might be hoping that the noise-canceling apparatus will take the shape of the 44 Magnum wielded by Dirty Harry, but in fact active sound control is not quite that active. The system might more properly be described as reactive, in that it responds to sound waves already headed toward human ears. In the configuration that is usual for such systems microphones detect the noise signal and send it to the system’s microprocessor, which almost instantly models it and creates its inverse for loudspeakers to fire at the original. Because the two sounds occupy the same range of frequencies and tones, the inverse sounds exactly like the noise it is to eliminate: the anti-noise cancelling Beethoven’s Fifth Symphony is heard as Beethoven’s Fifth. The only difference is that every positive pressure produced on the air by the orchestra is matched by a negative pressure produced by the computer, and every negative pressure is matched by a positive, thereby silencing the sound. The system is most effective as a kind of muffler, in which microphones, microprocessor, and loudspeaker are all in a unit encasing the device that produces the sound, stifling it at its source. But it can work as a headset, too, negating the sound at the last moment before it disturbs one’s peace of mind.
According to the passage, an active noise-cancellation system______.
选项
A、contains noise rather than negates it
B、eliminates noise rather than muffles it
C、deflects noise rather than baffles it
D、holds noise back rather than stifles it
答案
B
解析
本题的四个选项中,只有B项为正确答案。这可从文中第二段的最后一句“…which doesn’t just contain,deflect,or mask the noise,but annihilates it electronically”推知。
转载请注明原文地址:https://kaotiyun.com/show/nRhO777K
0
考博英语
相关试题推荐
Honestynolongerseemstobethebestpolicywithtellingofliesbecomingacommonpartofourdailylives.Anewresearchby
IhadvisitedthecapitalbeforealthoughmyfriendArthurhadnot,IfirstvisitedLondonasastudent,reluctantlyreleasedfr
ThestudyoflawhasbeenrecognizedforcenturiesasabasicintellectualdisciplineinEuropeanuniversities.However,onlyin
CantheInternethelppatientsjumpthelineatthedoctor’soffice?TheSiliconValleyEmployersForum,asophisticatedgroupo
CantheInternethelppatientsjumpthelineatthedoctor’soffice?TheSiliconValleyEmployersForum,asophisticatedgroupo
OnecountrythatiscertainoftheeffectoffilmsontourismisAustralia.TheTouristOfficeofQueenslandsaythatCrocodile
SincetheHawaiianIslandshaveneverbeenconnectedtootherlandmasses,thegreatvarietyofplantsinHawaiimustbearesult
SincetheHawaiianIslandshaveneverbeenconnectedtootherlandmasses,thegreatvarietyofplantsinHawaiimustbearesult
Researchhasproducedmanynew______thatwillbeusedinthemanufactureofavarietyofgoods.
Thatwasaman-madedisasterthatclearly______ifthefederalgovernment,specificallytheFederalEmergencyManagementAgency,
随机试题
关于组织出卖人体器官罪,下列哪一选项是错误的?()
图(a)梁因温度变化引起的弯矩如图(b),线膨胀系数为口,梁截面(矩形)高度为h,右端转角(顺时针为正)为()
Scientistswhostudythebrainhavefoundoutagreatdealabouthowwelearn.Theyhave【C1】______thatbabieslearnmuchmore
关于大肠杆菌RNA聚合酶的叙述,下列哪项是错误的?
当事人对已经发生法律效力的判决、裁定申请再审,是否适用于中止、中断和延长的说法正确的是()。
将金融产品以流动性、收益性、风险性和利率标准进行一般的排序,下列选项不正确的是()。
实行应税所得率方式核定征收企业所得税的纳税人,经营多业的,由税务机关根据多业项目分别确定适用的应税所得率。()
首先我申明,所有关于我写作风格转型的评论都_______,即使是与我的写作愿望_______的评论也是正确的。填入画横线部分最恰当的一项是:
Ifyoucan’tresistthechancetoputonabet,blameyourinsula—aregionofyourbrain.Scientiststhinkthatwhenthisbrain
Forthispart,youareallowed30minutestowriteashortessayentitledFollowYourOwnCoursebycommentingontheremark"Fo
最新回复
(
0
)