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| Listing 18. Dsp037.java. |
|---|
/* File Dsp037.java
Copyright 2004, R.G.BaldwinRevised 5/24/04
Illustrates filtering in the frequency domain.Performs FFT on an impulse. Eliminates all
energy between one-sixth and five-sixths of thesampling frequency by modifying the real and
imaginary parts of the FFT output. Then performsinverse FFT to produce the filtered impulse.
Run with Graph03.Tested using J2SE 1.4.2 under WinXP.
************************************************/import java.util.*;
class Dsp037 implements GraphIntfc01{final double pi = Math.PI;
int len = 256;double[] timeDataIn = new double[len];
double[]realSpect = new double[len];double[] imagSpect = new double[len];
double[]angle = new double[len];//unuseddouble[] magnitude = new double[len];
double[]timeOut = new double[len];public Dsp037(){//constructor
//Create the raw data pulsetimeDataIn[32] = 90;//Compute FFT of the time data and save it in
// the output arrays.ForwardRealToComplexFFT01.transform(
timeDataIn,realSpect,
imagSpect,angle,
magnitude);//Apply the frequency filter eliminating all
// energy between one-sixth and five-sixths// of the sampling frequency by modifying the
// real and imaginary parts of the spectrum.for(int cnt = len/6;cnt<5*len/6;cnt++){
realSpect[cnt]= 0.0;
imagSpect[cnt]= 0.0;
}//end for loop//Recompute the magnitude based on the
// modified real and imaginary spectra.for(int cnt = 0;cnt<len;cnt++){
magnitude[cnt]=
(Math.sqrt(realSpect[cnt]*realSpect[cnt]+ imagSpect[cnt]*imagSpect[cnt])/len);
}//end for loop//Compute inverse FFT of modified spectral
// data.InverseComplexToRealFFT01.inverseTransform(
realSpect,imagSpect,
timeOut);}//end constructor
//-------------------------------------------////The following six methods are required by the
// interface named GraphIntfc01.public int getNmbr(){
//Return number of curves to plot. Must not// exceed 5.
return 5;}//end getNmbr
//-------------------------------------------//public double f1(double x){
int index = (int)Math.round(x);if(index<0 || index>timeDataIn.length-1){
return 0;}else{
return timeDataIn[index];
}//end else}//end function
//-------------------------------------------//public double f2(double x){
int index = (int)Math.round(x);if(index<0 || index>realSpect.length-1){
return 0;}else{
return realSpect[index];
}//end else}//end function
//-------------------------------------------//public double f3(double x){
int index = (int)Math.round(x);if(index<0 || index>imagSpect.length-1){
return 0;}else{
return imagSpect[index];
}//end else}//end function
//-------------------------------------------//public double f4(double x){
int index = (int)Math.round(x);if(index<0 ||
index>magnitude.length-1){
return 0;}else{
//scale for convenient viewingreturn len*magnitude[index];}//end else
}//end function//-------------------------------------------//
public double f5(double x){int index = (int)Math.round(x);
if(index<0 ||
index>timeOut.length-1){
return0;
}else{//scale for convenient viewing
return 3.0*timeOut[index]/len;
}//end else}//end function
}//end sample class Dsp037 |
| Listing 19. Dsp038.java. |
|---|
/* File Dsp038.java
Copyright 2004, R.G.BaldwinRevised 5/24/04
Illustrates filtering in the frequency domain.Performs FFT on an impulse. Modifies the
complex spectrum. Then performs inverse FFTto produce the filtered impulse.
Run with Graph03.Tested using J2SE 1.4.2 under WinXP.
************************************************/import java.util.*;
class Dsp038 implements GraphIntfc01{final double pi = Math.PI;
int len = 256;double[] timeDataIn = new double[len];
double[]realSpect = new double[len];double[] imagSpect = new double[len];
double[]angle = new double[len];//unuseddouble[] magnitude = new double[len];
double[]timeOut = new double[len];public Dsp038(){//constructor
//Create the raw data pulsetimeDataIn[64] = 90;//Compute FFT of the time data and save it in
// the output arrays.ForwardRealToComplexFFT01.transform(
timeDataIn,realSpect,
imagSpect,angle,
magnitude);//Apply the frequency filter.
for(int cnt = 0;cnt<= len/2;cnt++){
if(cnt<3*len/32){
realSpect[cnt]= 0;
imagSpect[cnt]= 0;
}//end ifif(cnt>5*len/32){
realSpect[cnt]= 0;
imagSpect[cnt]= 0;
}//end if//Fold complex spectral data
if(cnt>0){
realSpect[len - cnt]= realSpect[cnt];}//end if
if(cnt>0){
imagSpect[len - cnt]= -imagSpect[cnt];}//end if
}//end for loop//Recompute the magnitude based on the
// modified real and imaginary spectra.for(int cnt = 0;cnt<len;cnt++){
magnitude[cnt]=
(Math.sqrt(realSpect[cnt]*realSpect[cnt]+ imagSpect[cnt]*imagSpect[cnt])/len);
}//end for loop//Compute inverse FFT of modified spectral
// data.InverseComplexToRealFFT01.inverseTransform(
realSpect,imagSpect,
timeOut);}//end constructor
//-------------------------------------------////The following six methods are required by the
// interface named GraphIntfc01.public int getNmbr(){
//Return number of curves to plot. Must not// exceed 5.
return 5;}//end getNmbr
//-------------------------------------------//public double f1(double x){
int index = (int)Math.round(x);if(index<0 || index>timeDataIn.length-1){
return 0;}else{
return timeDataIn[index];
}//end else}//end function
//-------------------------------------------//public double f2(double x){
int index = (int)Math.round(x);if(index<0 || index>realSpect.length-1){
return 0;}else{
return realSpect[index];
}//end else}//end function
//-------------------------------------------//public double f3(double x){
int index = (int)Math.round(x);if(index<0 || index>imagSpect.length-1){
return 0;}else{
return imagSpect[index];
}//end else}//end function
//-------------------------------------------//public double f4(double x){
int index = (int)Math.round(x);if(index<0 ||
index>magnitude.length-1){
return 0;}else{
//scale for convenient viewingreturn len*magnitude[index];}//end else
}//end function//-------------------------------------------//
public double f5(double x){int index = (int)Math.round(x);
if(index<0 ||
index>timeOut.length-1){
return 0;}else{
//scale for convenient viewingreturn 3.0*timeOut[index]/len;}//end else
}//end function}//end sample class Dsp038 |
This section contains a variety of miscellaneous information.
Baldwin illustrates and explains forward and inverse Fourier transforms using both DFT and FFT algorithms. He also illustrates and explains the implementation of frequency filtering by modifying the complex spectrum in the frequency domain and transforming the modified complex spectrum back into the time domain.
Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
-end-
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