How to plot the frequency response of a window?

Hi,

I am using hann(N), to generate a hanning window of length N. I want to plot the fft response of the window, I am using the below code:

N=16384;

Fs=1.024e6; Ts=1/Fs;

hn=hann(N);

y_hn=fft(hn,N);

y1_hn=(abs(y_hn))/N;

y2_hn=y1_hn(1:N/2);

y3_hn(1)=y2_hn(1);

y3_hn(2:N/2)=2*y2_hn(2:N/2);

y4_hn(1)=y3_hn(1);

y4_hn(2:N/2)=(y3_hn(2:N/2))/(2^(0.5));

y5_hn=20*log10(y4_hn);

f=(0:Fs/N:(Fs/2-Fs/N));

plot(f,y5_hn);

However the generate plot doesn't show any sidelobes (I compare with the plot generated by wvtool).

Could someone suggest how I can fix this?

[Chinmay Joshi]

Try using

N=16384;

Fs=1.024e6;

Ts=1/Fs;

hn=hann(2048);

f = [0:N-1]/N;

hn_abs=(abs(fft(hn,N)));

hn_ss=hn_abs(1:N/2);

hn_dc(1)=hn_ss(1);

hn_rest(2:N/2)=2*hn_ss(2:N/2);

hn_final(1)=hn_rest(1);

hn_final(2:N/2)=(hn_rest(2:N/2))./sqrt(2);

op=mag2db(hn_final);

%f=(0:Fs/N:(Fs/2-Fs/N));

plot(f(1:N/2),op);

the reason you were not getting the response that you were hoping for was that you were using too many data points (16384) for the window. you don't need to use as many window points as much as your fft points.

Answer 1

[Sanjana Chintalacheruvu]

Hi Ashutosh and Chinmay, I have a question. I have signal values ( not a function) from the testing data. where can I input these signal values in the code above? I am not familiar with this frequency analysis and I am trying to regenerate shaker result plots using different filters such as overlap, windowing in matlab. I only have excel file with signal values and time value. Thanks in advance!