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    Plotting frequency response to window sinc funtion in matlab

    I am taking DSP and the instructor explains theory but has not shown a single example all semester. One problem on the current homework assignment is to plot the frequency response of a windowed sinc filter using a Blackman window. The sample rate is 10 Khz and cutoff frequency is .195. He has given us M= 800. We are suposed to use the FFT instead of the freqz funtion to plot the normalized response in db from 1500 Hz to 2500 Hz. Here is the code I am trying to use, can anyone see anthing obvious I am missing. I have tried everything I could find so far online to try. The frequency response does look resonable when I use freqz(h).

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    fc = 0.1950;
    freq = linspace(1500, 2500, 801);
    s3 = 1;
    for n = 0: 800;   
        if n == 400
            d(s3) = 2*pi*fc;
        else
    d(s3) =  sin(2.* pi.*fc.*(n -400))./(n-400).*(0.42- 0.5 .*cos(n.*2.*pi./800)+0.08.*cos(n.*4.*pi/800));      
        end
    s3 = s3 +1;
    end
    ksum = sum(d);
    k = 1/ ksum;
    for n1 = 1: 801
        if n1 == 400
             h(n1) = 2*pi*fc.*k;
        else
            h(n1) = k * sin(2.* pi.*fc.*(n1 -400))./(n1-400).*(0.42- 0.5 .*cos(n1.*2.*pi./800)+0.08.*cos(n1.*4.*pi/800));   
        end  
    end
    H = fft(h,1024);
    for s= 1: 801
    ha(s) = (abs(H(s))./H(1));
    hdb(s) = 20*log10(ha(s));
    ahdb(s) =(-abs(hdb(s)));
    end
          
      plot(freq, ahdb), xlabel('Frequency (Hz)'), ylabel('Amplitude(dB)'), title('Frequency Response of Filter'), axis([1500 2500 -120 20]);
    Last edited by BradtheRad; 9th April 2016 at 23:45. Reason: added code formatted window

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