Quisk version 4.2.28

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
+}