NFM demod: phase discriminator refactoring. Review volume boundaries

include/dsp/phasediscri.hpp

@@ -18,33 +18,59 @@
 #ifndef INCLUDE_DSP_PHASEDISCRI_H_
 #define INCLUDE_DSP_PHASEDISCRI_H_
 
-/**
+class PhaseDiscriminators
- * 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);
+public:
-	m_m1Sample = sample;
+	/**
-	return (std::atan2(d.imag(), d.real()) / M_PI_2) * m_fmScaling;
+	 * Reset stored values
-}
+	 */
+	void reset()
+	{
+		m_m1Sample = 0;
+		m_m2Sample = 0;
+	}
 
-/**
+	/**
- * Alternative without atan at the expense of a slight distorsion on very wideband signals
+	 * Scaling factor so that resulting excursion maps to [-1,+1]
- * 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
+	void setFMScaling(Real fmScaling)
- */
+	{
-Real phaseDiscriminator2(const Complex& sample)
+		m_fmScaling = fmScaling;
-{
+	}
-	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;
+	 * 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;
+	}
 
-	return ((h1 - h2) / M_PI) * 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;
+	}
+
+private:
+	Complex m_m1Sample;
+	Complex m_m2Sample;
+	Real m_fmScaling;
+};
 
 #endif /* INCLUDE_DSP_PHASEDISCRI_H_ */

plugins/channel/nfm/nfmdemod.cpp

@@ -39,7 +39,6 @@ NFMDemod::NFMDemod() :
 	m_afSquelch(2, afSqTones),
 	m_audioFifo(4, 48000),
 	m_fmExcursion(2400),
-	m_fmScaling(384000/2400),
 	m_settingsMutex(QMutex::Recursive)
 {
 	setObjectName("NFMDemod");
@@ -49,10 +48,11 @@ NFMDemod::NFMDemod() :
 	m_config.m_rfBandwidth = 12500;
 	m_config.m_afBandwidth = 3000;
 	m_config.m_squelch = -30.0;
-	m_config.m_volume = 2.0;
+	m_config.m_volume = 1.0;
 	m_config.m_ctcssOn = false;
 	m_config.m_audioMute = false;
 	m_config.m_audioSampleRate = DSPEngine::instance()->getAudioSampleRate();
+	m_phaseDiscri.setFMScaling(384000/2400);
 
 	apply();
 
@@ -141,10 +141,10 @@ void NFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
 
 				m_AGC.feed(ci);
 
-				Real demod = phaseDiscriminator2(ci);
+				Real demod = m_phaseDiscri.phaseDiscriminator2(ci);
 
-				m_m2Sample = m_m1Sample;
+				//m_m2Sample = m_m1Sample;
-				m_m1Sample = ci;
+				//m_m1Sample = ci;
 				m_sampleCount++;
 
 				// AF processing
@@ -263,7 +263,7 @@ void NFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
 void NFMDemod::start()
 {
 	m_audioFifo.clear();
-	m_m1Sample = 0;
+	m_phaseDiscri.reset();
 }
 
 void NFMDemod::stop()
@@ -331,7 +331,7 @@ void NFMDemod::apply()
 		m_interpolator.create(16, m_config.m_inputSampleRate, m_config.m_rfBandwidth / 2.2);
 		m_interpolatorDistanceRemain = 0;
 		m_interpolatorDistance =  (Real) m_config.m_inputSampleRate / (Real) m_config.m_audioSampleRate;
-		m_fmScaling = m_config.m_inputSampleRate / m_fmExcursion;
+		m_phaseDiscri.setFMScaling(m_config.m_inputSampleRate / m_fmExcursion);
 		m_settingsMutex.unlock();
 	}
 
@@ -342,14 +342,14 @@ void NFMDemod::apply()
 		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 / 2.0f;
-		m_fmScaling = m_config.m_inputSampleRate / m_fmExcursion;
+		m_phaseDiscri.setFMScaling(m_config.m_inputSampleRate / m_fmExcursion);
 		m_settingsMutex.unlock();
 	}
 
 	if (m_config.m_squelch != m_running.m_squelch)
 	{
 		// input is a value in tenths of dB
-		m_squelchLevel = pow(10.0, m_config.m_squelch / 200.0);
+		m_squelchLevel = std::pow(10.0, m_config.m_squelch / 200.0);
 		//m_squelchLevel *= m_squelchLevel;
 		m_afSquelch.setThreshold(m_squelchLevel);
 	}

plugins/channel/nfm/nfmdemod.h

@@ -29,6 +29,7 @@
 #include "dsp/agc.h"
 #include "dsp/ctcssdetector.h"
 #include "dsp/afsquelch.h"
+#include "dsp/phasediscri.hpp"
 #include "audio/audiofifo.h"
 #include "util/message.h"
 
@@ -170,15 +171,15 @@ private:
 	double m_squelchLevel;
 
 	Real m_lastArgument;
-	Complex m_m1Sample;
+	//Complex m_m1Sample;
-	Complex m_m2Sample;
+	//Complex m_m2Sample;
 	MagAGC m_AGC;
 	AFSquelch m_afSquelch;
 	Real m_agcLevel; // AGC will aim to  this level
 	Real m_agcFloor; // AGC will not go below this level
 
 	Real m_fmExcursion;
-	Real m_fmScaling;
+	//Real m_fmScaling;
 
 	AudioVector m_audioBuffer;
 	uint m_audioBufferFill;
@@ -188,7 +189,7 @@ private:
 	NFMDemodGUI *m_nfmDemodGUI;
 	QMutex m_settingsMutex;
 
-#include "dsp/phasediscri.hpp"
+    PhaseDiscriminators m_phaseDiscri;
 
 	void apply();
 };

plugins/channel/nfm/nfmdemodgui.ui

@@ -244,7 +244,10 @@
       <item>
        <widget class="QSlider" name="volume">
         <property name="maximum">
-         <number>100</number>
+         <number>40</number>
+        </property>
+        <property name="pageStep">
+         <number>1</number>
         </property>
         <property name="value">
          <number>20</number>