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please tell me how this code works

loga (3)
could anyone tell me briefly how this code works?thank you..

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// nonrec_t.spc -- test program for non-recursive filter design 

  

#include "tools.h" 

#include "ltisys.h" 

#include "nonrec.h" 

  

int main() 

{ 

       Graph gr(3,2,"Non-Recursive Filter Design"); 

  

       // calculate low-pass filter and plot 

       LTISystem lp = NRLowPass(0.1,63); 

       lp.a.plot(gr,1,"Low-pass at 0.1","Samples","Amp"); 

  

       // calculate frequency response and plot 

       Spectrum lpf(500,1000); 

       for (int i=0;i<500;i++) lpf[i] = lp.response(i/1000.0); 

       lpf.plotLogMag(gr,2,"Frequency Response"); 

  

       // calculate high-pass filter and plot 

       LTISystem hp = NRHighPass(0.4,63); 

       hp.a.plot(gr,3,"High-pass at 0.4","Samples","Amp"); 

  

       // calculate frequency response and plot 

       Spectrum hpf(500,1000); 

       for (int i=0;i<500;i++) 

              hpf[i] = hp.response(i/1000.0); 

       hpf.plotLogMag(gr,4,"Frequency Response"); 

  

       // calculate band-pass filter and plot 

       LTISystem bp = NRBandPass(0.2,0.3,63); 

       bp.a.plot(gr,5,"Band-pass at 0.2-0.3","Samples","Amp"); 

  

       // calculate frequency response and plot 

       Spectrum bpf(500,1000); 

       for (int i=0;i<500;i++) bpf[i] = bp.response(i/1000.0); 

       bpf.plotLogMag(gr,6,"Frequency Response"); 

        

       gr.close(); 

} 


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// kaiser_t.cpp -- test program for Kaiser window design 

  

#include "tools.h" 

#include "ltisys.h" 

#include "nonrec.h" 

#include "kaiser.h" 

  

const int MAXKAISERWIN=256; // maximum window length 

  

// Create non-recursive low-pass filter using Kaiser window 

LTISystem KaiserLowPass( 

       double freq,         // corner freq 

                           //  (fraction of sampling rate) 

       double ripple,       // allowed ripple (dB) 

       double twidth        // transition width 

                           //  (fraction of sampling rate) } 

       )                    // returns LTI System 

{ 

       int    i; 

  

       // get (half-)Kaiser window 

       Waveform kwin = Kaiser(ripple,twidth,MAXKAISERWIN); 

       int nhalf = kwin.count()-1; 

  

       // generate one half of coefficients from 

       //     windowed sinc() function 

       double omega = 2*PI*freq; 

       for (i=0;i<=nhalf;i++) 

              kwin[i+1] *= omega*sinc(i*omega)/PI; 

  

       // copy into LTI System 

       LTISystem lpfilt(2*nhalf,0); 

       lpfilt.a[nhalf] = kwin[1]; 

       for (i=1;i<=nhalf;i++) { 

              lpfilt.a[nhalf-i] = kwin[i+1]; 

              lpfilt.a[nhalf+i] = kwin[i+1]; 

       } 

  

       return lpfilt; 

} 
  



  

int main() 

{ 

       int    i; 

  

       // initialise graphics 

       Graph gr (2,2,"Kaiser Window Design"); 

  

       // plot Kaiser window 1 

       Waveform kwv1 = Kaiser(40.0,0.005,MAXKAISERWIN); 

       kwv1.plot(gr,1,"Kaiser (40dB/0.005)"); 

  

       // calculate and plot frequency response 

       LTISystem lp1 = KaiserLowPass(0.1,40.0,0.005); 

       Spectrum lpf1(500,1000); 

       for (i=0;i<500;i++) lpf1[i] = lp1.response(i/1000.0); 

       lpf1.plotLogMag(gr,2,"Frequency Response"); 

  

       // plot Kaiser window 2 

       Waveform kwv2 = Kaiser(80.0,0.01,MAXKAISERWIN); 

       kwv2.plot(gr,3,"Kaiser (80dB/0.01)"); 

  

       // calculate and plot frequency response 

       LTISystem lp2 = KaiserLowPass(0.1,80.0,0.01); 

       Spectrum lpf2(500,1000); 

       for (i=0;i<500;i++) lpf2[i] = lp2.response(i/1000.0); 

       lpf2.plotLogMag(gr,4,"Frequency Response"); 

  

       gr.close(); 

}
Graham (15)
Is this from CSound?

It appears to be two mathematical functions for modifying and analyzing waveforms.
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