9.26阅读一

It is now possible to hear a recording of Caruso’s singing that is far superior to any made during his lifetime. A decades-old way-cylinder recording of this great operatic tenor has been digitized, and the digitized signal has been processed by computer to remove the extraneous sound, or “noise,” introduced by the now “ancient” wax-cylinder recording process.

开头举了一个例子，说现在可以听到音质最好的Caruso’s singing，因为wax-cylinder recording造成的noise已经被digital signal消除了。（引出下文对digital signal的介绍）

Although this digital technique needs improvements, it represents a new and superior way of recording and processing sound which overcomes many of the limitations of analog recording. In analog recording systems, the original sound is represented as a continuous waveform created by variations in the sound’s amplitude over time. When analog playback systems reproduce this waveform, however, they invariably introduce distortions. First, the waveform produced during playback differs somewhat from the original waveform. Second, the medium that stores the analog recording creates noise during playback which gets added to the recorded sounds.

说明analog recording出现noise的原因，即通过连续的波来记录不同的振幅，但是在播放时这些波会出现不同程度的偏差，导致杂音。(便于下一段具体介绍为什么digital signal可以消除这些杂音）

Digital recordings, by contrast, reduce the original sound to a series of discrete numbers that represent the sound’s waveform. Because the digital playback system “reads” only numbers, any noise and distortion that may accumulate during storage and manipulation of the digitized signal will have little effect: as long as the numbers remain recognizable, the original waveform will be reconstructed with little loss in quality.

说明digital的进步之处，即相对于analog recording， digital signal是通过离散的数字来记录声波的tid，只要这些离散的数字还在，音色就不会被影响。

However, because the waveform is continuous, while its digital representation is composed of discrete numbers, it is impossible for digital systems to avoid some distortion.

digital signal虽然可以消除传统的analog rcording中出现的而杂音问题，但是由于声波是连续的而digital signal是离散的，因而也不可避免会出现问题。

One kind of distortion, called “sampling error,” occurs if the sound is sample (i.e., its amplitude is measured) too infrequently, so that the amplitude changes more than one quantum (the smallest change in amplitude measured by the digital system) between samplings. In effect, the sound is changing too quickly for the system to record it accurately.

第一种问题就是sampling error，就是如果记录的频率小于声波的频率的话，就没有办法记录下完整的声音（想想动画片的制作，如果每秒画的数量少于肉眼可以辨识的数量的话就会看起来很卡）

A second form of distortion is “quantizing error,” which arises when the amplitude being measured is not a whole number of quanta, forcing the digital recorder to round off. Over the long term, these errors are random, and the noise produced (a background buzzing) is similar to analog noise except that it only occurs when recorded sounds are being reproduced.

第二种问题就是quanting error，就是如果振幅不是一个整数的quanta（意思可能是指介于在两种声音信号之间），digital recorder就会四舍五入，使得记录的音质不够准确。这种问题和nanlog recording中出现的相似，但是只会出现在复制时（相当于拿重配的钥匙再去配钥匙，配出来的钥匙不能用差不多的意思）

272. Which of the following best describes the relationship of the first paragraph to the passage as a whole?

(A) The first paragraph introduces a general thesis that is elaborated on in detail elsewhere in the passage.

(B) The first paragraph presents a concrete instance of a problem that is discussed elsewhere in the passage.

(C) The first paragraph describes a traditional process that is contrasted unfavorably with a newer process described elsewhere in the passage.

(D) The first paragraph presents a dramatic example of the potential of a process that is described elsewhere in the passage.

(E) The first paragraph describes a historic incident that served as the catalyst for developments described elsewhere in the passage.

273. According the passage, one of the ways in which analog recording systems differ from digital recording systems is that analog systems

(A) can be used to reduce background noise in old recordings

(B) record the original sound as a continuous waveform

(C) distort the original sound somewhat

(D) can avoid introducing extraneous and nonmusical sounds

(E) can reconstruct the original waveform with little loss inequality

A选项，说反了，analog systems并不能消除杂音，消除杂音的是digital recording. B选项，In analog recording systems, the original sound is represented as a continuous waveform created by variations in the sound’s amplitude over time，对的。 C选项，并不是distort the original sound， 而是掺入了杂音。DE都说反了。

274. Which of the following statements about the numbers by which sound is represented in a digital system can be inferred from the passage?

(A) They describe the time interval between successive sounds in a passage of music.

(B) They model large changes in the amplitude of the initial sound with relatively poor precision.

(C) They are slightly altered each time they are read by the playback apparatus.

(D) They are not readily altered by distortion and noise accumulated as the digital signal is stored and manipulated.

(E) They are stored in the recording medium in small groups that can be read simultaneously by the playback apparatus.

275. Which of the following can be inferred from the passage about the digital approach to the processing of sound?

(A) It was developed in competition with wax-cylinder recording technology.

(B) It has resulted in the first distortion-free playback system.

(C) It has been extensively applied to nonmusical sounds.

(D) It cannot yet process music originally recorded on analog equipment.

(E) It is not yet capable of reprocessing old recordings in a completely distortion-free manner.