Question

Consider the following MATLAB code using the handel.mat example file that comes with MATLAB: >> load handel; >> ys = y(1000:1000+100); >> ysw = ys.*blackman(length(ys)); >> [X,f] = SpectrumAnalysis(ysw,Fs,2^12); where SpectrumAnalysis is a user defined function that computes an N-point FFT (i.e. 2^12 points), to an input signal ys with a sampling frequency Fs. Which of the following statements about the spectrum of ys is correct?

A) The effect of using the blackman window is that the sidelobes due to the rectangular window are eliminated creating a better estimate of the true underlying spectrum. The computational resolution is slightly less but the frequency resolution is higher than using the rectangular window.

B) The effect of using the blackman window is that the sidelobes due to the rectangular window are eliminated creating a better estimate of the true underlying spectrum. The computational and the frequency resolution do not change when using the blackman window

C) The effect of using the blackman window is that the sidelobes due to the rectangular window reduced creating a better estimate of the true underlying spectrum. The computational and the frequency resolution do not change when using the blackman window.

D) The effect of using the blackman window is that the sidelobes due to the rectangular window are reduced creating a better estimate of the true underlying spectrum. The computational resolution is the same but the frequency resolution is slightly less than using the rectangular window.

Answer 1

The frequency resolution is the ability to discern two closely spaced frequencies at similar power levels (therefore a metric of what that spacing is would be the frequency resolution).

From above figure and above definition side lobes are reduced when using Blackman window compared to rectangular window but not eliminated. But frequency resolution increases. So from all options given above option A is correct but side lobes are not eliminated but reduced.