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#include "pv.h"
/* S is a spectrum in rfft format, i.e., it contains N real values
arranged as real followed by imaginary values, except for first
two values, which are real parts of 0 and Nyquist frequencies;
convert first changes these into N/2+1 PAIRS of magnitude and
phase values to be stored in output array C; the phases are then
unwrapped and successive phase differences are used to compute
estimates of the instantaneous frequencies for each phase vocoder
analysis channel; decimation rate D and sampling rate R are used
to render these frequency values directly in Hz. */
void convert(float *S, float *C, int N2, float *lastphase, float fundamental, float factor )
{
float phase,
phasediff;
int real,
imag,
amp,
freq;
float a,
b;
int i;
float myTWOPI, myPI;
myTWOPI = 8.*atan(1.);
myPI = 4.*atan(1.);
for ( i = 0; i <= N2; i++ ) {
imag = freq = ( real = amp = i<<1 ) + 1;
a = ( i == N2 ? S[1] : S[real] );
b = ( i == 0 || i == N2 ? 0. : S[imag] );
C[amp] = hypot( a, b );
if ( C[amp] == 0. )
phasediff = 0.;
else {
phasediff = ( phase = -atan2( b, a ) ) - lastphase[i];
lastphase[i] = phase;
while ( phasediff > myPI )
phasediff -= myTWOPI;
while ( phasediff < -myPI )
phasediff += myTWOPI;
}
C[freq] = phasediff*factor + i*fundamental;
/*
if( i > 8 && i < 12 ) {
fprintf(stderr,"convert freq %d: %f\n",i, C[freq]);
}
*/
}
}
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