我正在使用 FFT 类来获取基频。我正在传递一些双值的数组。数组就像队列。当添加新值时数组将被更新。但我的问题是输出数组会不时变得很大。其变为E的幂值并最终返回NaN。我使用下面的 FFT 类，我很困惑问题出在哪里。如果任何人都可以通过找出原因来提供帮助，那将是一个很大的帮助。
这是我的 FFT 类(class)
public class FFT {
int n, m;
// Lookup tables. Only need to recompute when size of FFT changes.
double[] cos;
double[] sin;
double[] window;
public FFT(int n) {
this.n = n;
this.m = (int)(Math.log(n) / Math.log(2));
// Make sure n is a power of 2
if(n != (1<<m))
throw new RuntimeException("FFT length must be power of 2");
// precompute tables
cos = new double[n/2];
sin = new double[n/2];
// for(int i=0; i<n/4; i++) {
// cos[i] = Math.cos(-2*Math.PI*i/n);
// sin[n/4-i] = cos[i];
// cos[n/2-i] = -cos[i];
// sin[n/4+i] = cos[i];
// cos[n/2+i] = -cos[i];
// sin[n*3/4-i] = -cos[i];
// cos[n-i] = cos[i];
// sin[n*3/4+i] = -cos[i];
// }
for(int i=0; i<n/2; i++) {
cos[i] = Math.cos(-2*Math.PI*i/n);
sin[i] = Math.sin(-2*Math.PI*i/n);
}
makeWindow();
}
protected void makeWindow() {
// Make a blackman window:
// w(n)=0.42-0.5cos{(2*PI*n)/(N-1)}+0.08cos{(4*PI*n)/(N-1)};
window = new double[n];
for(int i = 0; i < window.length; i++)
window[i] = 0.42 - 0.5 * Math.cos(2*Math.PI*i/(n-1))
+ 0.08 * Math.cos(4*Math.PI*i/(n-1));
}
public double[] getWindow() {
return window;
}
/***************************************************************
* fft.c
* Douglas L. Jones
* University of Illinois at Urbana-Champaign
* January 19, 1992
* http://cnx.rice.edu/content/m12016/latest/
*
* fft: in-place radix-2 DIT DFT of a complex input
*
* input:
* n: length of FFT: must be a power of two
* m: n = 2**m
* input/output
* x: double array of length n with real part of data
* y: double array of length n with imag part of data
*
* Permission to copy and use this program is granted
* as long as this header is included.
****************************************************************/
public void fft(double[] x, double[] y)
{
int i,j,k,n1,n2,a;
double c,s,e,t1,t2;
// Bit-reverse
j = 0;
n2 = n/2;
for (i=1; i < n - 1; i++) {
n1 = n2;
while ( j >= n1 ) {
j = j - n1;
n1 = n1/2;
}
j = j + n1;
if (i < j) {
t1 = x[i];
x[i] = x[j];
x[j] = t1;
t1 = y[i];
y[i] = y[j];
y[j] = t1;
}
}
// FFT
n1 = 0;
n2 = 1;
for (i=0; i < m; i++) {
n1 = n2;
n2 = n2 + n2;
a = 0;
for (j=0; j < n1; j++) {
c = cos[a];
s = sin[a];
a += 1 << (m-i-1);
for (k=j; k < n; k=k+n2) {
t1 = c*x[k+n1] - s*y[k+n1];
t2 = s*x[k+n1] + c*y[k+n1];
x[k+n1] = x[k] - t1;
y[k+n1] = y[k] - t2;
x[k] = x[k] + t1;
y[k] = y[k] + t2;
}
}
}
}
// Test the FFT to make sure it's working
public static void main(String[] args) {
int N = 8;
FFT fft = new FFT(N);
double[] window = fft.getWindow();
double[] re = new double[N];
double[] im = new double[N];
// Impulse
re[0] = 1; im[0] = 0;
for(int i=1; i<N; i++)
re[i] = im[i] = 0;
beforeAfter(fft, re, im);
// Nyquist
for(int i=0; i<N; i++) {
re[i] = Math.pow(-1, i);
im[i] = 0;
}
beforeAfter(fft, re, im);
// Single sin
for(int i=0; i<N; i++) {
re[i] = Math.cos(2*Math.PI*i / N);
im[i] = 0;
}
beforeAfter(fft, re, im);
// Ramp
for(int i=0; i<N; i++) {
re[i] = i;
im[i] = 0;
}
beforeAfter(fft, re, im);
long time = System.currentTimeMillis();
double iter = 30000;
for(int i=0; i<iter; i++)
fft.fft(re,im);
time = System.currentTimeMillis() - time;
System.out.println("Averaged " + (time/iter) + "ms per iteration");
}
protected static void beforeAfter(FFT fft, double[] re, double[] im) {
System.out.println("Before: ");
printReIm(re, im);
fft.fft(re, im);
System.out.println("After: ");
printReIm(re, im);
}
protected static void printReIm(double[] re, double[] im) {
System.out.print("Re: [");
for(int i=0; i<re.length; i++)
System.out.print(((int)(re[i]*1000)/1000.0) + " ");
System.out.print("]\nIm: [");
for(int i=0; i<im.length; i++)
System.out.print(((int)(im[i]*1000)/1000.0) + " ");
System.out.println("]");
}
}
下面是我在 android 中使用 FFT 实例的主要 Activity 类
public class MainActivity extends Activity implements SensorEventListener{
static final float ALPHA = 0.15f;
private int count=0;
private static GraphicalView view;
private LineGraph line = new LineGraph();
private static Thread thread;
private SensorManager mSensorManager;
private Sensor mAccelerometer;
TextView title,tv,tv1,tv2,tv3,tv4,tv5,tv6;
RelativeLayout layout;
private double a;
private double m = 0;
private float p,q,r;
public long[] myList;
public double[] myList2;
public double[] gettedList;
static String k1,k2,k3,k4;
int iniX=0;
public FFT fft;
public myArray myArrayQueue;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fft=new FFT(128);
myList=new long[128];
myList2=new double[128];
gettedList=new double[128];
myArrayQueue=new myArray(128);
//get the sensor service
mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
//get the accelerometer sensor
mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
//get layout
layout = (RelativeLayout)findViewById(R.id.relative);
LinearLayout layout = (LinearLayout) findViewById(R.id.layoutC);
view= line.getView(this);
layout.addView(view);
//get textviews
title=(TextView)findViewById(R.id.name);
//tv=(TextView)findViewById(R.id.xval);
//tv1=(TextView)findViewById(R.id.yval);
//tv2=(TextView)findViewById(R.id.zval);
tv3=(TextView)findViewById(R.id.TextView04);
tv4=(TextView)findViewById(R.id.TextView01);
tv5=(TextView)findViewById(R.id.TextView02);
tv6=(TextView)findViewById(R.id.TextView03);
for (int i = 0; i < myList2.length; i++){
myList2[i] =0;
}
}
public final void onAccuracyChanged(Sensor sensor, int accuracy)
{
// Do something here if sensor accuracy changes.
}
@Override
public final void onSensorChanged(SensorEvent event)
{
count=+1;
// Many sensors return 3 values, one for each axis.
float x = event.values[0];
float y = event.values[1];
float z = event.values[2];
//float[] first={x,y,z};
// float[] larst={p,q,r};
//larst= lowPass(first,larst);
//double FY= b.Filter(y);
//double FZ= b.Filter(z);
//get merged value
// m = (float) Math.sqrt(larst[0]*larst[0]+larst[1]*larst[1]+larst[2]*larst[2]);
m=(double)Math.sqrt(x*x+y*y+z*z);
//display values using TextView
//title.setText(R.string.app_name);
//tv.setText("X axis" +"\t\t"+x);
//tv1.setText("Y axis" + "\t\t" +y);
//tv2.setText("Z axis" +"\t\t" +z);
//myList[iniX]=m*m;
//myList[iniX+1]=myList[iniX];
iniX=+1;
//myList[3]=myList[2];
//myList[2]=myList[1];
//myList[1]=myList[0];
myArrayQueue.insert(m*m);
gettedList=myArrayQueue.getMyList();
/* for(int a = myList.length-1;a>0;a--)
{
myList[a]=myList[a-1];
}
myList[0]=m*m;
*/
fft.fft(gettedList, myList2);
k1=Double.toString(myList2[0]);
k2=Double.toString(myList2[1]);
k3=Double.toString(myList2[2]);
k4=Double.toString(myList2[3]);
tv3.setText("[0]= "+k1);
tv4.setText("[1]= "+k2);
tv5.setText("[2]= "+k3);
tv6.setText("[3]= "+k4);
line.addNewPoint(iniX,(float) m);
view.repaint();
}
@Override
protected void onResume()
{
super.onResume();
mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);
}
@Override
protected void onPause()
{
super.onPause();
mSensorManager.unregisterListener(this);
}
public void LineGraphHandler(View view){
}
//Low pass filter
protected float[] lowPass( float[] input, float[] output ) {
if ( output == null ) return input;
for ( int i=0; i<input.length; i++ ) {
output[i] = output[i] + ALPHA * (input[i] - output[i]);
}
return output;
}
/*@Override
public void onStart(){
super.onStart();
view= line.getView(this);
setContentView(view);
}*/
}
最佳答案
如果输入包含 NaN，FFT 输出只会产生 NaN。因此，在调用 FFT 来调试代码之前，请显式检查 FFT 的输入数组是否有任何超出范围的值。然后从那里倒推找出它们来自哪里。
关于java - FFT 返回变为 NaN 的大值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18547679/