RC Question...with CR Stem?!

[PFWinkler]

SOURCE: MBA.com FREE practice question

Question is regarding the CR question stem (ie: inference question)...within a RC passage. First time I've seen this, and frankly, I cant recall anything from the OG with a similar structure. Just wondering if anyone has any additional inputs, or has seen CR stems used with RC passages! Thanks!

This passage was written in 1984.
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 wax-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.

Although this digital technique needs improvement, 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.

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. 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. One kind of distortion, called “sampling error,” occurs if the sound is sampled (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. 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.

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

1) They describe the time interval between successive sounds in a passage of music.
2) They model large changes in the amplitude of the initial sound with relatively poor precision.
3) They are slightly altered each time they are read by the playback apparatus.
4) They are not readily altered by distortion and noise accumulated as the digital signal is stored and manipulated.
5) They are stored in the recording medium in small groups that can be read simultaneously by the playback apparatus.

[PFWinkler]

OA: 4) They are not readily altered by distortion and noise accumulated as the digital signal is stored and manipulated.

[RonPurewal]

this is a normal RC detail question, like any other RC detail question. i'm not sure what makes you think it is unique/unusual; it isn't.

as for any other RC detail question...
• use the question to determine exactly what you have to go find in the passage
• go find that information
• pick the answer choice that re-states / "recycles" the same information

if we find the part of the passage that talks about those numbers, we see this:
any noise and distortion that may accumulate during storage and manipulation of the digitized signal will have little effect

the correct answer basically just says this again, in a slightly different way.

[JustinCKN]

Dear Ron,

I don't know what is wrong with B
" they model large changes in the amplitude of the initial sound with relatively poor precision."

in the passage,
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.

If amplitude changes more than one quantum will result in distortion, can this prove that "large changes in the amplitude of the initial sound result in poor precision?

[esledge]

Hi Justin,
Everything is good with (B) up to a certain point in the text: “they (the numbers) model large changes in the amplitude of the initial sound.” In fact, the numbers model the amplitude of the initial sound in general, whether the amplitude is changing a lot or a little.

However, the end of the choice, “with relatively poor precision,” is not supported by the passage. The proof sentence you cite…

in the passage,
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.

… implies that the playback might sound weird as the digital playback jumps suddenly from (I’m making up numbers here) 10 to 16, but it does not imply that either the measurement of 10 or the measurement of 16 is wrong or imprecise—just that the jump between them is not “smooth” during playback.

I think you might have read “poor precision” as “poor recreation of the original sound,” whereas (B) is using “poor precision” to refer to how the numbers “model large changes in the amplitude,” which is not exactly the same.

[JustinCKN]

Hi esledge,

Thanks for your detailed explanation. I understand the subtle difference you explain. I just wonder during the nervous GMAT process, how can I screen those tiny differences. it is so challenging.

Have a good one.

[esledge]

Hi esledge,

Thanks for your detailed explanation. I understand the subtle difference you explain. I just wonder during the nervous GMAT process, how can I screen those tiny differences. it is so challenging.

Have a good one.

I'm glad it was helpful.

I'm not sure there's a universal rule, as the topics and wording subtleties can vary. However it does help me to approach verbal with a "finding fault" attitude. I don't look for the right answer, I look for anything that could make an answer wrong, continuing until 4 answers are eliminated. On my scrap paper, if it's definitely wrong, I put an X next to the choice letter. If it's possibly wrong, I put a squiggle mark. Then, if I have 2 X's and 2 squiggles, and one choice with no doubts at all, I pick the no-doubt choice. If I have 3 X's and 2 squiggles, I weigh the two squiggle choices against each other--this helps tune out the extra noise if a decision does come down to tiny differences.