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BFM demod: apply de-emphasis

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This commit is contained in:
f4exb 2015-12-08 02:00:30 +01:00
parent 2f8fda7137
commit e533997dbe
6 changed files with 138 additions and 22 deletions
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2
CMakeLists.txt
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@ -79,6 +79,7 @@ set(sdrbase_SOURCES
sdrbase/dsp/fftengine.cpp
sdrbase/dsp/fftfilt.cxx
sdrbase/dsp/fftwindow.cpp
sdrbase/dsp/filterrc.cpp
sdrbase/dsp/filesink.cpp
sdrbase/dsp/interpolator.cpp
sdrbase/dsp/inthalfbandfilter.cpp
@ -155,6 +156,7 @@ set(sdrbase_HEADERS
include/dsp/fftfilt.h
include/dsp/fftwengine.h
include/dsp/fftwindow.h
include/dsp/filterrc.h
include/dsp/filesink.h
include/dsp/gfft.h
include/dsp/interpolator.h

50
include/dsp/filterrc.h Normal file
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@ -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_FILTERRC_H_
#define INCLUDE_DSP_FILTERRC_H_
#include "dsp/dsptypes.h"
/** First order low-pass IIR filter for real-valued signals. */
class LowPassFilterRC
{
public:
/**
* Construct 1st order low-pass IIR filter.
*
* timeconst :: RC time constant in seconds (1 / (2 * PI * cutoff_freq)
*/
LowPassFilterRC(Real timeconst);
/**
* Reconfigure filter with new time constant
*/
void configure(Real timeout);
/** Process samples. */
void process(const Real& sample_in, Real& sample_out);
private:
Real m_timeconst;
Real m_y1;
Real m_a1;
Real m_b0;
};
#endif /* INCLUDE_DSP_FILTERRC_H_ */

28
plugins/channel/bfm/bfmdemod.cpp
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@ -32,7 +32,9 @@ BFMDemod::BFMDemod(SampleSink* sampleSink) :
m_sampleSink(sampleSink),
m_audioFifo(4, 250000),
m_settingsMutex(QMutex::Recursive),
m_pilotPLL(19000/384000, 50/384000, 0.01)
m_pilotPLL(19000/384000, 50/384000, 0.01),
m_deemphasisFilterX(default_deemphasis * 48000 * 1.0e-6),
m_deemphasisFilterY(default_deemphasis * 48000 * 1.0e-6)
{
setObjectName("BFMDemod");
@ -43,6 +45,8 @@ BFMDemod::BFMDemod(SampleSink* sampleSink) :
m_config.m_squelch = -60.0;
m_config.m_volume = 2.0;
m_config.m_audioSampleRate = DSPEngine::instance()->getAudioSampleRate(); // normally 48 kHz
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);
apply();
@ -120,7 +124,7 @@ void BFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
m_m1Sample = rf[i];
m_sampleBuffer.push_back(Sample(demod * (1<<15), 0.0));
quint16 sampleStereo;
Real sampleStereo;
// Process stereo if stereo mode is selected
@ -135,7 +139,7 @@ void BFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
if (m_interpolatorStereo.interpolate(&m_interpolatorStereoDistanceRemain, s, &cs))
{
sampleStereo = (qint16)(cs.real() * 3000 * m_running.m_volume);
sampleStereo = cs.real();
}
}
@ -143,15 +147,19 @@ void BFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
if (m_interpolator.interpolate(&m_interpolatorDistanceRemain, e, &ci))
{
quint16 sample = (qint16)(ci.real() * 3000 * m_running.m_volume);
if (m_running.m_audioStereo)
{
m_audioBuffer[m_audioBufferFill].l = sample + sampleStereo;
m_audioBuffer[m_audioBufferFill].r = sample - sampleStereo;
Real deemph_l, deemph_r; // Pre-emphasis is applied on each channel before multiplexing
m_deemphasisFilterX.process(ci.real() + sampleStereo, deemph_l);
m_deemphasisFilterY.process(ci.real() - sampleStereo, deemph_r);
m_audioBuffer[m_audioBufferFill].l = (qint16)(deemph_l * 3000 * m_running.m_volume);
m_audioBuffer[m_audioBufferFill].r = (qint16)(deemph_r * 3000 * m_running.m_volume);
}
else
{
Real deemph;
m_deemphasisFilterX.process(ci.real() + sampleStereo, deemph);
quint16 sample = (qint16)(deemph * 3000 * m_running.m_volume);
m_audioBuffer[m_audioBufferFill].l = sample;
m_audioBuffer[m_audioBufferFill].r = sample;
}
@ -319,6 +327,12 @@ void BFMDemod::apply()
m_squelchLevel *= m_squelchLevel;
}
if (m_config.m_audioSampleRate != m_running.m_audioSampleRate)
{
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_running.m_inputSampleRate = m_config.m_inputSampleRate;
m_running.m_inputFrequencyOffset = m_config.m_inputFrequencyOffset;
m_running.m_rfBandwidth = m_config.m_rfBandwidth;

5
plugins/channel/bfm/bfmdemod.h
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@ -27,6 +27,7 @@
#include "dsp/movingaverage.h"
#include "dsp/fftfilt.h"
#include "dsp/phaselock.h"
#include "dsp/filterrc.h"
#include "audio/audiofifo.h"
#include "util/message.h"
@ -147,6 +148,10 @@ private:
StereoPhaseLock m_pilotPLL;
Real m_pilotPLLSamples[2];
LowPassFilterRC m_deemphasisFilterX;
LowPassFilterRC m_deemphasisFilterY;
static const Real default_deemphasis = 50.0; // 50 us
void apply();
};

58
sdrbase/dsp/filterrc.cpp Normal file
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@ -0,0 +1,58 @@
///////////////////////////////////////////////////////////////////////////////////
// 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/>. //
///////////////////////////////////////////////////////////////////////////////////
#include <QDebug>
#include "dsp/filterrc.h"
// Construct 1st order low-pass IIR filter.
LowPassFilterRC::LowPassFilterRC(Real timeconst) :
m_timeconst(timeconst),
m_y1(0)
{
m_a1 = - exp(-1/m_timeconst);
m_b0 = 1 + m_a1;
}
// Reconfigure
void LowPassFilterRC::configure(Real timeconst)
{
m_timeconst = timeconst;
m_y1 = 0;
m_a1 = - exp(-1/m_timeconst);
m_b0 = 1 + m_a1;
qDebug() << "LowPassFilterRC::configure: t: " << m_timeconst
<< " a1: " << m_a1
<< " b0: " << m_b0;
}
// Process samples.
void LowPassFilterRC::process(const Real& sample_in, Real& sample_out)
{
/*
* Continuous domain:
* H(s) = 1 / (1 - s * timeconst)
*
* Discrete domain:
* H(z) = (1 - exp(-1/timeconst)) / (1 - exp(-1/timeconst) / z)
*/
m_y1 = (sample_in * m_b0) - (m_y1 * m_a1);
sample_out = m_y1;
}

17
sdrbase/dsp/phaselock.cpp
View File

@ -81,6 +81,7 @@ PhaseLock::PhaseLock(Real freq, Real bandwidth, Real minsignal)
m_sample_cnt = 0;
}
void PhaseLock::configure(Real freq, Real bandwidth, Real minsignal)
{
qDebug("PhaseLock::configure: freq: %f bandwidth: %f minsignal: %f", freq, bandwidth, minsignal);
@ -142,6 +143,7 @@ void PhaseLock::configure(Real freq, Real bandwidth, Real minsignal)
m_sample_cnt = 0;
}
// Process samples. Bufferized version
void PhaseLock::process(const std::vector<Real>& samples_in, std::vector<Real>& samples_out)
{
@ -247,21 +249,6 @@ void PhaseLock::process(const std::vector<Real>& samples_in, std::vector<Real>&
m_sample_cnt += n;
}
/*
void PhaseLock::process(const Real& sample_in, Real& sample_out)
{
m_phase += m_freq;
if (m_phase > 2.0 * M_PI) {
m_phase -= 2.0 * M_PI;
}
Real psin = sin(m_phase);
Real pcos = cos(m_phase);
sample_out = 2 * psin * pcos;
}*/
// Process samples. Multiple output
void PhaseLock::process(const Real& sample_in, Real *samples_out)