/******************************************************************
* calculate deconvolution filter 1/(s[w]+water_level).
* the water-level is c*auto-correlation(s[t]). A low-pass gaussian filter
* exp(-w^2/(4 sigma^2))
* is also applied.
******************************************************************/
void water(
complex *a, /* IN/OUT, spectrum of s(t) */
int nft, /* number of pts of s(w), 2^N*/
float dt, /* sampling interval in sec */
float c, /* water-level in %*/
float gauss /* sigma in Hz */
)
{
int j;
float w, delw;
double *d2, agg, water, u;
u = 1+c;
d2 = (double *) malloc ((nft+1)*sizeof(double));
delw = PI/(dt*nft);
d2[0] = a[0].x*a[0].x;
d2[nft] = a[0].y*a[0].y;
water = d2[0]+d2[nft];
for (j=1; j<nft; j++) {
d2[j] = a[j].x*a[j].x+a[j].y*a[j].y;
water += d2[j];
}
water = c*water/nft; /* in terms of auto-correlation */
a[0].x *= u/(d2[0]+water);
for (w=delw,j=1; j<nft; j++,w+=delw) {
agg = 0.5*w/gauss;
a[j] = dmltp(u*exp(-agg*agg)/(d2[j]+water),conjg(a[j]));
}
agg = 0.5*w/gauss;
a[0].y *= u*exp(-agg*agg)/(d2[j]+water);
free(d2);
}
complex cinvs(complex a) {
complex dmltp(float, complex);
complex conjg(complex a);
return(dmltp(1./(a.x*a.x+a.y*a.y), conjg(a)));
}
