Help with FFT and wvtool

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Leor Greenberger 2013-3-9

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https://ww2.mathworks.cn/matlabcentral/answers/66467-help-with-fft-and-wvtool

Hi All,

I am stumped on this one. I created a filter and used wvtool on it.

w_k = kaiser(K,9.5*pi);
wvtool(w_k)

I then set the analysis parameters as follows:

And I get the plot shown below. I have tried every which way to recreate this myself so that I can calculate the main lobe width of various filters to no avail. Ideally, I want the magnitude normalized and response in dB (see first image), but when I couldn't get those plots, I tried to just copy what I have pasted here. My code is as follows (although I have tried many variations of normalizing the FFT to no avail):

K = 512;
Fs = 1E6;
w_k = kaiser(K,9.5*pi);
W_n = fft(w_k,K);
W_n = W_n(1:K/2+1);
W_n = abs(W_n);
W_n = 2*W_n;
n = 0:1:K/2;
freq_n = Fs*n/K;
figure
plot(freq_n/1E6,W_n);

Thanks for the help!

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Honglei Chen 2013-3-10

编辑：Honglei Chen 2013-3-10

Not sure if I understand your issue. In the plots above, the span in time domain is about 0.8 seconds and if you want to sample it with 1 MHz, you need a length of 8e5, not 512. So could you describe what you meant to do?

Leor Greenberger 2013-3-11

Hi Honglei,

I am not sure what the time domain plot is based on, but I set 512 points in the FFT, as shown in the first image, and this is the length I am using in the script.

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