ITPEC IP April 2024 Question 1
Sound signals are digitized. Sampling is performed at Time 1 through Time 5 in the figure below, and four-level quantization is performed; in other words, the levels closest to the sampling point are selected. After that, two-bit encoding is performed. The result is “11 01 00 10 11”. When digitization is performed in the same way, which of the following figures represents the sound signal that results in “01 00 10 11 01”?
Explanation
Figure (b) — its samples at Times 1 to 5 round to the levels 01, 00, 10, 11, 01.
At each sampling time, read the height of the curve and take the nearest of the four levels; the five 2-bit codes in time order are the result. The example checks the method: its curve is near 11, 01, 00, 10, 11 at the five times, giving 11 01 00 10 11. Reading the four figures the same way:
Only (b) gives 01 00 10 11 01.
Answer (b)
Why not others:
- •(a) — gives
01 01 00 10 11: the curve is still at 01 at Time 2, where 00 is needed, and every later sample is off as well - •(c) — gives
01 00 10 11 10: right for four samples, but at Time 5 the curve has fallen only a little from its peak and is nearest 10, not 01 - •(d) — gives
01 00 10 10 01: its peak lies between Times 3 and 4, and by Time 4 the line is back just below 10, so it quantizes to 10 instead of 11
Key rule: Quantization rounds each sample to the nearest level, so only the height at the sampling instants counts; peaks and dips between two samples leave no trace in the code.
Multimedia · AI-written, may contain errors
This question comes from an official ITPEC past paper. ITPEC Practice is an independent study tool and is not affiliated with ITPEC. See the official IP past-paper collection or Report an issue.