Added a simple CTCSS detector based on Goertzel's algorithm

CMakeLists.txt

@@ -51,6 +51,7 @@ set(sdrbase_SOURCES
 
 	sdrbase/dsp/channelizer.cpp
 	sdrbase/dsp/channelmarker.cpp
+	sdrbase/dsp/ctcssdetector.cpp
 	sdrbase/dsp/dspcommands.cpp
 	sdrbase/dsp/dspengine.cpp
 	sdrbase/dsp/fftengine.cpp

include-gpl/dsp/ctcssdetector.h

@@ -0,0 +1,88 @@
+/*
+ * ctcssdetector.h
+ *
+ *  Created on: Jun 16, 2015
+ *      Author: f4exb
+ *      See: http://www.embedded.com/design/connectivity/4025660/Detecting-CTCSS-tones-with-Goertzel-s-algorithm
+ */
+
+#ifndef INCLUDE_GPL_DSP_CTCSSDETECTOR_H_
+#define INCLUDE_GPL_DSP_CTCSSDETECTOR_H_
+
+#include "dsp/dsptypes.h"
+
+/** CTCSSDetector: Continuous Tone Coded Squelch System
+ * tone detector class based on the Modified Goertzel
+ * algorithm.
+ */
+class CTCSSDetector {
+public:
+    // Constructors and Destructor
+    CTCSSDetector();
+    // allows user defined CTCSS tone set
+    CTCSSDetector(int _nTones, Real *tones);
+    virtual ~CTCSSDetector();
+
+    // setup the basic parameters and coefficients
+    void setCoefficients(
+    		int N,            // the algorithm "block"  size
+			int SampleRate);  // input signal sample rate
+
+    // set the detection threshold
+    void setThreshold(double thold);
+
+    // analyze a sample set and optionally filter
+    // the tone frequencies.
+    bool analyze(Real *sample); // input signal sample
+
+    // get the number of defined tones.
+    int getNTones() const {
+    	return nTones;
+    }
+
+    // get the tone set
+    const Real *getToneSet() const
+    {
+    	return toneSet;
+    }
+
+    // get the currently detected tone, if any
+    bool getDetectedTone(int &maxTone) const
+    {
+    	maxTone = maxPowerIndex;
+    	return toneDetected;
+    }
+
+    // Get the max power at the detected tone.
+    Real getMaxPower() const
+    {
+    	return maxPower;
+    }
+
+    void reset();                       // reset the analysis algorithm
+
+protected:
+    // Override these to change behavior of the detector
+    virtual void initializePower();
+    virtual void evaluatePower();
+    void feedback(Real sample);
+    void feedForward();
+
+private:
+    int N;
+    int sampleRate;
+    int nTones;
+    int samplesProcessed;
+    int maxPowerIndex;
+    bool toneDetected;
+    Real maxPower;
+    Real *k;
+    Real *coef;
+    Real *toneSet;
+    Real *u0;
+    Real *u1;
+    Real *power;
+};
+
+
+#endif /* INCLUDE_GPL_DSP_CTCSSDETECTOR_H_ */

sdrbase/dsp/ctcssdetector.cpp

@@ -0,0 +1,204 @@
+/*
+ * ctcssdetector.cpp
+ *
+ *  Created on: Jun 16, 2015
+ *      Author: f4exb
+ */
+#include <cmath>
+#include "dsp/ctcssdetector.h"
+
+CTCSSDetector::CTCSSDetector() :
+			N(0),
+			sampleRate(0),
+			samplesProcessed(0),
+			maxPowerIndex(0),
+			toneDetected(false),
+			maxPower(0.0)
+{
+	nTones = 32;
+	k = new Real[nTones];
+	coef = new Real[nTones];
+	toneSet = new Real[nTones];
+	u0 = new Real[nTones];
+	u1 = new Real[nTones];
+	power = new Real[nTones];
+
+	// The 32 EIA standard tones
+	toneSet[0]  = 67.0;
+	toneSet[1]  = 71.9;
+	toneSet[2]  = 74.4;
+	toneSet[3]  = 77.0;
+	toneSet[4]  = 79.7;
+	toneSet[5]  = 82.5;
+	toneSet[6]  = 85.4;
+	toneSet[7]  = 88.5;
+	toneSet[8]  = 91.5;
+	toneSet[9]  = 94.8;
+	toneSet[10]  = 97.4;
+	toneSet[11] = 100.0;
+	toneSet[12] = 103.5;
+	toneSet[13] = 107.2;
+	toneSet[14] = 110.9;
+	toneSet[15] = 114.8;
+	toneSet[16] = 118.8;
+	toneSet[17] = 123.0;
+	toneSet[18] = 127.3;
+	toneSet[19] = 131.8;
+	toneSet[20] = 136.5;
+	toneSet[21] = 141.3;
+	toneSet[22] = 146.2;
+	toneSet[23] = 151.4;
+	toneSet[24] = 156.7;
+	toneSet[25] = 162.2;
+	toneSet[26] = 167.9;
+	toneSet[27] = 173.8;
+	toneSet[28] = 179.9;
+	toneSet[29] = 186.2;
+	toneSet[30] = 192.8;
+	toneSet[31] = 203.5;
+}
+
+CTCSSDetector::CTCSSDetector(int _nTones, Real *tones) :
+			N(0),
+			sampleRate(0),
+			samplesProcessed(0),
+			maxPowerIndex(0),
+			toneDetected(false),
+			maxPower(0.0)
+{
+	nTones = _nTones;
+	k = new Real[nTones];
+	coef = new Real[nTones];
+	toneSet = new Real[nTones];
+	u0 = new Real[nTones];
+	u1 = new Real[nTones];
+	power = new Real[nTones];
+
+	for (int j = 0; j < nTones; ++j)
+	{
+		toneSet[j] = tones[j];
+	}
+}
+
+
+CTCSSDetector::~CTCSSDetector()
+{
+	delete[] k;
+	delete[] coef;
+	delete[] toneSet;
+	delete[] u0;
+	delete[] u1;
+	delete[] power;
+}
+
+
+void CTCSSDetector::setCoefficients(int _N, int _samplerate )
+{
+	N = _N;                   // save the basic parameters for use during analysis
+	sampleRate = _samplerate;
+
+	// for each of the frequencies (tones) of interest calculate
+	// k and the associated filter coefficient as per the Goertzel
+	// algorithm. Note: we are using a real value (as apposed to
+	// an integer as described in some references. k is retained
+	// for later display. The tone set is specified in the
+	// constructor. Notice that the resulting coefficients are
+	// independent of N.
+	for (int j = 0; j < nTones; ++j)
+	{
+		k[j] = ((double)N * toneSet[j]) / (double)sampleRate;
+		coef[j] = 2.0 * cos((2.0 * M_PI * toneSet[j])/(double)sampleRate);
+	}
+}
+
+
+// Analyze an input signal for the presence of CTCSS tones.
+bool CTCSSDetector::analyze(Real *sample)
+{
+
+	feedback(*sample); // Goertzel feedback
+	samplesProcessed += 1;
+
+	if (samplesProcessed == N) // completed a block of N
+	{
+		feedForward(); // calculate the power at each tone
+		samplesProcessed = 0;
+		return true; // have a result
+	}
+	else
+	{
+		return false;
+	}
+}
+
+
+void CTCSSDetector::feedback(Real in)
+{
+	Real t;
+
+	// feedback for each tone
+	for (int j = 0; j < nTones; ++j)
+	{
+		t = u0[j];
+		u0[j] = in + (coef[j] * u0[j]) - u1[j];
+		u1[j] = t;
+	}
+}
+
+
+void CTCSSDetector::feedForward()
+{
+	initializePower();
+
+	for (int j = 0; j < nTones; ++j)
+	{
+		power[j] = (u0[j] * u0[j]) + (u1[j] * u1[j]) - (coef[j] * u0[j] * u1[j]);
+		u0[j] = u1[j] = 0.0; // reset for next block.
+	}
+
+	evaluatePower();
+}
+
+
+void CTCSSDetector::reset()
+{
+	for (int j = 0; j < nTones; ++j)
+	{
+		power[j] = u0[j] = u1[j] = 0.0; // reset
+	}
+
+	samplesProcessed = 0;
+	maxPower = 0.0;
+	maxPowerIndex = 0;
+	toneDetected = false;
+}
+
+
+void CTCSSDetector::initializePower()
+{
+	for (int j = 0; j < nTones; ++j)
+	{
+		power[j] = 0.0; // reset
+	}
+}
+
+
+void CTCSSDetector::evaluatePower()
+{
+	Real sumPower = 0.0;
+	Real aboveAvg = 10.0; // Arbitrary max power above average threshold
+	maxPower = 0.0;
+
+	for (int j = 0; j < nTones; ++j)
+	{
+		sumPower += power[j];
+
+		if (power[j] > maxPower)
+		{
+			maxPower = power[j];
+			maxPowerIndex = j;
+		}
+	}
+
+	toneDetected = (maxPower > (sumPower/nTones) + aboveAvg);
+}