问在Android中计算歌曲的FFT

EN

implementation 'com.github.wendykierp:JTransforms:3.1'

double Fs = 8000;
double T = 1/Fs;
int L = 1600;

double freq = 338;

double sinValue_re_im[] = new double[L*2]; // because FFT takes an array where its positions alternate between real and imaginary
for( int i = 0; i < L; i++)
{
    sinValue_re_im[2*i] = Math.sin( 2*Math.PI*freq*(i * T) ); // real part
    sinValue_re_im[2*i+1] = 0; //imaginary part
}

// matlab
// tf = fft(y1);

DoubleFFT_1D fft = new DoubleFFT_1D(L);
fft.complexForward(sinValue_re_im);
double[] tf = sinValue_re_im.clone();

// matlab
// P2 = abs(tf/L);
double[] P2 = new double[L];
for(int i=0; i<L; i++){

    double re = tf[2*i]/L;
    double im = tf[2*i+1]/L;
    P2[i] = sqrt(re*re+im*im);
}

// P1 = P2(1:L/2+1);
double[] P1 = new double[L/2]; // single-sided: the second half of P2 has the same values as the first half
System.arraycopy(P2, 0, P1, 0, L/2);
// P1(2:end-1) = 2*P1(2:end-1);
System.arraycopy(P1, 1, P1, 1, L/2-2);
for(int i=1; i<P1.length-1; i++){
    P1[i] = 2*P1[i];
}
// f = Fs*(0:(L/2))/L;
double[] f = new double[L/2 + 1];
for(int i=0; i<L/2+1;i++){
    f[i] = Fs*((double) i)/L;
}