第四章测试1.The process to obtain a finite-length sequence by truncating a very long sequence is often called the windowing.（ ）
A:对 B:错
答案:A
2.The N-point DFT sequence
is precisely the set of frequency samples of the Fourier transform
of the length-M sequence
at N equally spaced frequencies
.（ ）A:错 B:对 3.For a given finite-length sequence, its periodic extension can be expressed as （ ）.
A:
B:
C:None of the other options are correct
D:
4.Circular convolution can be obtained from taking the periodic extension for linear convolution first, and then taking the principal-value range.（ ）A:错 B:对 5.In physical applications, the implementation of linear convolution using a circular convolution should involve in FFT algorithms, which is called fast convolution.（ ）
A:错 B:对 6.For the following sequence types, whose DFT are conjugate-symmetric? （ ）
A:unit sample sequence B:sinusoidal sequence C:rectangular sequence D:unit step sequence 7.For the DTFT
of a length-M sequence 
, We sample
at N equally spaced points
. If N is less then M, then the time-domain aliasing will occur.（ ）A:错 B:对 8.In the first step of analyzing a continuous-time signal using the DFT, selection of the sampling frequency
should be higher than two times of the maximum frequency
.（ ）A:错 B:对 9.The improvement method of the frequency resolution is to increase the effective time-record length
.（ ）A:对 B:错 10.Zero-padding operation can improve the ability of the frequency resolution.（ ）
A:对 B:错 11.As for analyzing the spectrum of a continuous-time signal using the DFT, the shorter the truncated signal is, the smaller the truncation error will be.（ ）
A:错 B:对 12.As for analyzing the spectrum of a continuous-time signal using the DFT, some parameters are given here, including the highest frequency fh of signal, the sampling frequency Fs , and the transform interval length N of DFT. The exact analog frequency fk corresponding to the frequency index k, can be determined using the formula （ ）.
A:fk=Fs×k/N B:fk=2fh×k/N C:fk=fh×k/N D:fk=2Fs×k/N
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