VE7UWU
/
sdrangel
mirror of https://github.com/f4exb/sdrangel.git
1
0
Fork 0
Code Issues Projects Releases Wiki Activity

NFM demod: phase discriminator refactoring. Review volume boundaries

This commit is contained in:
f4exb 2015-12-17 00:45:44 +01:00
parent 28bde131ba
commit 3028357718
4 changed files with 68 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

74
include/dsp/phasediscri.hpp
View File

@ -18,33 +18,59 @@
#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)
class PhaseDiscriminators
{
Complex d(std::conj(m_m1Sample) * sample);
m_m1Sample = sample;
return (std::atan2(d.imag(), d.real()) / M_PI_2) * m_fmScaling;
}
public:
/**
* 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
* 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;
/**
* Scaling factor so that resulting excursion maps to [-1,+1]
*/
void setFMScaling(Real fmScaling)
{
m_fmScaling = fmScaling;
}
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_ */

18
plugins/channel/nfm/nfmdemod.cpp
View File

@ -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_m1Sample = ci;
//m_m2Sample = m_m1Sample;
//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);
}

9
plugins/channel/nfm/nfmdemod.h
View File

@ -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_m2Sample;
//Complex m_m1Sample;
//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();
};

5
plugins/channel/nfm/nfmdemodgui.ui
View File

@ -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>