BFM demod: implemented phase discriminator in a separate utility class

plugins/channel/bfm/bfmdemod.cpp

@@ -37,8 +37,7 @@ BFMDemod::BFMDemod(SampleSink* sampleSink, RDSParser *rdsParser) :
 	m_pilotPLL(19000/384000, 50/384000, 0.01),
 	m_deemphasisFilterX(default_deemphasis * 48000 * 1.0e-6),
 	m_deemphasisFilterY(default_deemphasis * 48000 * 1.0e-6),
-	m_fmExcursion(default_excursion),
+	m_fmExcursion(default_excursion)
-	m_fmScaling(384000/m_fmExcursion)
 {
 	setObjectName("BFMDemod");
 
@@ -52,6 +51,7 @@ BFMDemod::BFMDemod(SampleSink* sampleSink, RDSParser *rdsParser) :
 	m_deemphasisFilterX.configure(default_deemphasis * m_config.m_audioSampleRate * 1.0e-6);
 	m_deemphasisFilterY.configure(default_deemphasis * m_config.m_audioSampleRate * 1.0e-6);
 	m_rfFilter = new fftfilt(-50000.0 / 384000.0, 50000.0 / 384000.0, rfFilterFftLength);
+	m_phaseDiscri.setFMScaling(384000/m_fmExcursion);
 
 	apply();
 
@@ -124,7 +124,7 @@ void BFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
 				m_squelchState--;
 
 				//demod = phaseDiscriminator2(rf[i], msq);
-				demod = phaseDiscriminator(rf[i]);
+				demod = m_phaseDiscri.phaseDiscriminator(rf[i]);
 			}
 			else
 			{
@@ -248,7 +248,7 @@ void BFMDemod::start()
 {
 	m_squelchState = 0;
 	m_audioFifo.clear();
-	m_m1Sample = 0;
+	m_phaseDiscri.reset();
 }
 
 void BFMDemod::stop()
@@ -354,7 +354,7 @@ void BFMDemod::apply()
 		Real lowCut = -(m_config.m_rfBandwidth / 2.0) / m_config.m_inputSampleRate;
 		Real hiCut  = (m_config.m_rfBandwidth / 2.0) / m_config.m_inputSampleRate;
 		m_rfFilter->create_filter(lowCut, hiCut);
-		m_fmScaling = m_config.m_inputSampleRate / m_fmExcursion;
+		m_phaseDiscri.setFMScaling(m_config.m_inputSampleRate / m_fmExcursion);
 		m_settingsMutex.unlock();
 
 		qDebug() << "BFMDemod::handleMessage: m_rfFilter->create_filter: sampleRate: "

plugins/channel/bfm/bfmdemod.h

@@ -28,6 +28,7 @@
 #include "dsp/fftfilt.h"
 #include "dsp/phaselock.h"
 #include "dsp/filterrc.h"
+#include "dsp/phasediscri.h"
 #include "audio/audiofifo.h"
 #include "util/message.h"
 #include "rdsdemod.h"
@@ -184,8 +185,6 @@ private:
 	Real m_squelchLevel;
 	int m_squelchState;
 
-	Complex m_m1Sample; //!< x^-1 complex sample
-	Complex m_m2Sample; //!< x^-2 complex sample
 	Real m_m1Arg; //!> x^-1 real sample
 
 	MovingAverage<Real> m_movingAverage;
@@ -210,37 +209,9 @@ private:
 	static const Real default_deemphasis = 50.0; // 50 us
 
 	Real m_fmExcursion;
-	Real m_fmScaling;
 	static const int default_excursion = 750000; // +/- 75 kHz
 
-	/**
+	PhaseDiscriminators m_phaseDiscri;
-	 * 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();
 };

plugins/channel/wfm/wfmdemodgui.ui

@@ -243,6 +243,9 @@
         <property name="maximum">
          <number>100</number>
         </property>
+        <property name="pageStep">
+         <number>1</number>
+        </property>
         <property name="value">
          <number>20</number>
         </property>