1、计算机专业英语Unit 8 MultimediaComputer EnglishBackground Knowledge 背景知识背景知识v多媒体技术是指一种对文本、声音、图形、多媒体技术是指一种对文本、声音、图形、图像、动画、视频等多媒体信息进行采集、图像、动画、视频等多媒体信息进行采集、存储、加工或集成的计算机技术。存储、加工或集成的计算机技术。v多媒体技术已经深入到我们生活、工作和多媒体技术已经深入到我们生活、工作和学习的各个方面，例如可视电话、视频会学习的各个方面，例如可视电话、视频会议、远程医疗、电子出版等等。议、远程医疗、电子出版等等。v声音是一种重要的信息载体，如何让计算声音是一
2、种重要的信息载体，如何让计算机能够处理声音是多媒体技术中重要的一机能够处理声音是多媒体技术中重要的一部分。部分。Computer EnglishNew Words and Useful Expressionsvibrate/vabret/振动,激动,颤动;使颤动,使摆动,使振动sensitive/senstv/敏感的;神经过敏的;易受伤害的;易怒的sensation/sensen/感觉,知觉;轰动,激动;感觉能力,知觉作用;pitch/pt/音高,声音相对的高低graphically/grfkli/通过图表;轮廓分明地;生动地waveform/wevf:m/波形diagram/dagrm/图表
3、plot/plt/划分,绘图axis/kss/轴Computer EnglishNew Words and Useful Expressionstuning/tun/调音,调律fork/fk/叉peak/pk/山顶,山峰;高峰,最高点,顶端;trough/trf/槽volt/vlt/伏特digitiz(s)ation/ddatazen/数字化reconstruct/riknstrkt/重建,再建modulation/mdjle n/调制uncompressed未经压缩的,没有压缩的Computer EnglishNew Words and Useful Expressionsquantizat
4、ion/kwntzen/量化analogue/nlg/相似物;类似物;类似情况n o r m a l i z(s)a t i o n/n:mlasen/正常化;标准化;正态化maximiz(s)e/mksmaz/最大化harmonic/hmnk/谐波;谐函数;和声high(low)-pitched声调高(低)的 vertical(y)axis垂直(y)轴horizontal(x)axis水平(X)轴Computer EnglishNew Words and Useful Expressionstuning fork音叉sample rate采样率，样本率，采样速度Pulse Code Modu
5、lation(PCM)称脉冲编码调制quantization error量化误差analogue signal模拟信号rounding errors舍入误差garbage noise噪音double bass低音提琴jazz drumming爵士鼓Computer EnglishSound Conceptv Something vibrates,it makes the air vibrate,the air vibrates the sensitive bones in your ear,and this sensation is registered in your brain as so
6、und.L o g oL o g oSound Representation Diagramv The size of the vibrations is plotted on the vertical(y)axis and the time it was measured at is plotted on the horizontal(x)axis.L o g oL o g oDigitizationv The way a natural thing such as sound is digitized is replicating the way the ear works.v Inste
7、ad of sensitive bones,you have sensitive material that will vibrate just like the bones in your ear do.These vibrations then cause an electrical current to be created.v This translates the amplitude of a sound to an electrical voltage difference.L o g oL o g oDigitization Diagramv Essentially what y
8、ou will get is the exact same diagram as above but instead the y axis will be volts.This can then be measured and converted into binary that computers can use.L o g oL o g oAudio Propertiesv audio has two properties:bits and sample rate.v Bits(or Binary digITS)is the amount of different voltages(amp
9、litudes)that can be sampled.So,just as 8bit video only has 256 colors,8bit audio only has 256 different amplitudes it can sample.v Sample Rate is the amount of times every second that the audio is sampled or given a binary number.CDs are sampled at 44.1 KHz or 44,100 times a second.16bit 44.1 KHz au
10、dio means-65,536 possible levels measured 44,100 times a second.L o g oL o g oPCMv This system of digitizing audio is known as Pulse Code Modulation(PCM).v The most common of these is 16bit 44.1 KHz audio as found on CDs.L o g oL o g oSample Rate and Recreation ComparisonL o g oL o g oGarbage Noise&
11、Normalizationv The peaks and troughs of the incoming sound beyond the range of the sampling system to the tops and bottoms of the peaks are clipped which causes the garbage noise.v If you want to increase the volume(gain)without creating garbage data,this process is called Normalization.L o g oL o g
12、 oNormalization Processv 1)Finds the highest amplitude of any wave in the audiov 2)Amplifies the entire audio wave so that this amplitude does not exceed the maximum that can be stored in binary-i.e.without clipping.v Essentially the principle is to find the maximum gain without clipping any of your
13、 peaks.-Best Effort,sometimes clipping is unavoidable.L o g oL o g oComplexity of Soundv Not only is there more than one sound but this sound is also made up of harmonics and other audio wonders that make the instruments and voices sound the way they do.v There are a few recognizable patterns but because the waveforms are combined,it is difficult to separate sounds of different instruments in one waveform.
