NFM demod: adjust phase discriminator settings. Put in in a separate header

CMakeLists.txt

@@ -167,8 +167,9 @@ set(sdrbase_HEADERS
 	include/dsp/misc.h
 	include/dsp/movingaverage.h
 	include/dsp/nco.h
+	include/dsp/phasediscri.hpp
 	include/dsp/phaselock.h
-    sdrbase/dsp/pidcontroller.h
+        sdrbase/dsp/pidcontroller.h
 	include/dsp/samplefifo.h
 	include/dsp/samplesink.h
 	include/dsp/nullsink.h

include/dsp/phasediscri.hpp

@@ -0,0 +1,50 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2015 F4EXB                                                      //
+// written by Edouard Griffiths                                                  //
+//                                                                               //
+// This program is free software; you can redistribute it and/or modify          //
+// it under the terms of the GNU General Public License as published by          //
+// the Free Software Foundation as version 3 of the License, or                  //
+//                                                                               //
+// This program is distributed in the hope that it will be useful,               //
+// but WITHOUT ANY WARRANTY; without even the implied warranty of                //
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                  //
+// GNU General Public License V3 for more details.                               //
+//                                                                               //
+// You should have received a copy of the GNU General Public License             //
+// along with this program. If not, see <http://www.gnu.org/licenses/>.          //
+///////////////////////////////////////////////////////////////////////////////////
+
+#ifndef INCLUDE_DSP_PHASEDISCRI_H_
+#define INCLUDE_DSP_PHASEDISCRI_H_
+
+/**
+ * Standard discriminator using atan2. On modern processors this is as efficient as the non atan2 one.
+ * This is better for high fidelity.
+ */
+Real phaseDiscriminator(const Complex& sample)
+{
+	Complex d(std::conj(m_m1Sample) * sample);
+	m_m1Sample = sample;
+	return (std::atan2(d.imag(), d.real()) / M_PI_2) * m_fmScaling;
+}
+
+/**
+ * Alternative without atan at the expense of a slight distorsion on very wideband signals
+ * http://www.embedded.com/design/configurable-systems/4212086/DSP-Tricks--Frequency-demodulation-algorithms-
+ * in addition it needs scaling by instantaneous magnitude squared and volume (0..10) adjustment factor
+ */
+Real phaseDiscriminator2(const Complex& sample)
+{
+	Real ip = sample.real() - m_m2Sample.real();
+	Real qp = sample.imag() - m_m2Sample.imag();
+	Real h1 = m_m1Sample.real() * qp;
+	Real h2 = m_m1Sample.imag() * ip;
+
+	m_m2Sample = m_m1Sample;
+	m_m1Sample = sample;
+
+	return ((h1 - h2) / M_PI) * m_fmScaling;
+}
+
+#endif /* INCLUDE_DSP_PHASEDISCRI_H_ */

plugins/channel/nfm/nfmdemod.cpp

@@ -38,8 +38,8 @@ NFMDemod::NFMDemod() :
 	m_audioMute(false),
 	m_afSquelch(2, afSqTones),
 	m_audioFifo(4, 48000),
-	m_fmExcursion(4800),
+	m_fmExcursion(2400),
-	m_fmScaling(384000/4800),
+	m_fmScaling(384000/2400),
 	m_settingsMutex(QMutex::Recursive)
 {
 	setObjectName("NFMDemod");
@@ -141,7 +141,7 @@ void NFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
 
 				m_AGC.feed(ci);
 
-				Real demod = phaseDiscriminator2(ci, 0.5);
+				Real demod = phaseDiscriminator2(ci);
 
 				m_m2Sample = m_m1Sample;
 				m_m1Sample = ci;
@@ -341,7 +341,7 @@ void NFMDemod::apply()
 		m_settingsMutex.lock();
 		m_lowpass.create(301, m_config.m_audioSampleRate, 250.0);
 		m_bandpass.create(301, m_config.m_audioSampleRate, 300.0, m_config.m_afBandwidth);
-		m_fmExcursion = m_config.m_afBandwidth;
+		m_fmExcursion = m_config.m_afBandwidth / 2.0f;
 		m_fmScaling = m_config.m_inputSampleRate / m_fmExcursion;
 		m_settingsMutex.unlock();
 	}

plugins/channel/nfm/nfmdemod.h

@@ -188,34 +188,7 @@ private:
 	NFMDemodGUI *m_nfmDemodGUI;
 	QMutex m_settingsMutex;
 
-	/**
+#include "dsp/phasediscri.hpp"
-	 * Standard discriminator using atan2. On modern processors this is as efficient as the non atan2 one.
-	 * This is better for high fidelity.
-	 */
-	Real phaseDiscriminator(const Complex& sample)
-	{
-		Complex d(std::conj(m_m1Sample) * sample);
-		m_m1Sample = sample;
-		return (std::atan2(d.imag(), d.real()) / M_PI_2) * m_fmScaling;
-	}
-
-	/**
-	 * Alternative without atan at the expense of a slight distorsion on very wideband signals
-	 * http://www.embedded.com/design/configurable-systems/4212086/DSP-Tricks--Frequency-demodulation-algorithms-
-	 * in addition it needs scaling by instantaneous magnitude squared and volume (0..10) adjustment factor
-	 */
-	Real phaseDiscriminator2(const Complex& sample, Real msq)
-	{
-		Real ip = sample.real() - m_m2Sample.real();
-		Real qp = sample.imag() - m_m2Sample.imag();
-		Real h1 = m_m1Sample.real() * qp;
-		Real h2 = m_m1Sample.imag() * ip;
-
-		m_m2Sample = m_m1Sample;
-		m_m1Sample = sample;
-
-		return ((h1 - h2) / (msq * M_PI)) * m_fmScaling;
-	}
 
 	void apply();
 };