quisk-kc4upr/extdemod.c

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#include <Python.h>
#include <stdlib.h>
#include <math.h>
#include <complex.h>
#include "quisk.h"
// If you set add_extern_demod in your config file, you will get another
// button that will call this module. Change it to what you want. Save
// a copy because new releases of Quisk will overwrite this file.
//
// NOTE: NEW RELEASES OF QUISK WILL OVERWRITE THIS FILE!
int quisk_extern_demod(complex double * cSamples, int nSamples, double decim)
{ // Filter and demodulate the I/Q samples into audio play samples.
// cSamples: The input I/Q samples, and the output stereo play samples.
// nSamples: The number of input samples; maximum is SAMP_BUFFER_SIZE.
// decim: The decimation needed (1.0 for no decimation).
// The output play samples are stereo, and are placed into cSamples.
// The return value is the number of output samples = nSamples / decim.
// See quisk.h for useful data in quisk_sound_state. For example, the
// sample rate is quisk_sound_state.sample_rate. If you need decimation,
// look at iDecimate() and fDecimate() in quisk.c.
int i;
double d, di;
complex double cx;
static complex double fm_1 = 10; // Sample delayed by one
static complex double fm_2 = 10; // Sample delayed by two
if (fabs (decim - 1.0) > 0.001) // no provision for decimation
return 0;
for (i = 0; i < nSamples; i++) { // narrow FM
cx = cSamples[i];
di = creal(fm_1) * (cimag(cx) - cimag(fm_2)) -
cimag(fm_1) * (creal(cx) - creal(fm_2));
d = creal(fm_1) * creal(fm_1) + cimag(fm_1) * cimag(fm_1);
if (d == 0) // I don't think this can happen
di = 0;
else
di = di / d * quisk_sound_state.sample_rate;
fm_2 = fm_1; // fm_2 is sample cSamples[i - 2]
fm_1 = cx; // fm_1 is sample cSamples[i - 1]
cSamples[i] = di + I * di; // monophonic sound, two channels
}
return nSamples; // Number of play samples
}