From d2c31059dd4814cfc8365c76499e21fdeaf723fe Mon Sep 17 00:00:00 2001
From: f4exb <f4exb06@gmail.com>
Date: Wed, 29 May 2019 11:23:28 +0200
Subject: [PATCH] AM demod: implemented low pass filter after the demod

---
 plugins/channelrx/demodam/amdemod.cpp | 6 ++++++
 plugins/channelrx/demodam/amdemod.h   | 1 +
 2 files changed, 7 insertions(+)

diff --git a/plugins/channelrx/demodam/amdemod.cpp b/plugins/channelrx/demodam/amdemod.cpp
index 9ed8f1303..d6be41e0a 100644
--- a/plugins/channelrx/demodam/amdemod.cpp
+++ b/plugins/channelrx/demodam/amdemod.cpp
@@ -260,6 +260,10 @@ void AMDemod::processOneSample(Complex &ci)
             demod = m_bandpass.filter(demod);
             demod /= 301.0f;
         }
+        else
+        {
+            demod = m_lowpass.filter(demod);
+        }
 
         Real attack = (m_squelchCount - 0.05f * m_audioSampleRate) / (0.05f * m_audioSampleRate);
         sample = demod * StepFunctions::smootherstep(attack) * (m_audioSampleRate/24) * m_settings.m_volume;
@@ -383,6 +387,7 @@ void AMDemod::applyAudioSampleRate(int sampleRate)
     m_interpolatorDistanceRemain = 0;
     m_interpolatorDistance = (Real) m_inputSampleRate / (Real) sampleRate;
     m_bandpass.create(301, sampleRate, 300.0, m_settings.m_rfBandwidth / 2.0f);
+    m_lowpass.create(301, sampleRate,  m_settings.m_rfBandwidth / 2.0f);
     m_audioFifo.setSize(sampleRate);
     m_squelchDelayLine.resize(sampleRate/5);
     DSBFilter->create_dsb_filter((2.0f * m_settings.m_rfBandwidth) / (float) sampleRate);
@@ -456,6 +461,7 @@ void AMDemod::applySettings(const AMDemodSettings& settings, bool force)
         m_interpolatorDistanceRemain = 0;
         m_interpolatorDistance = (Real) m_inputSampleRate / (Real) m_audioSampleRate;
         m_bandpass.create(301, m_audioSampleRate, 300.0, settings.m_rfBandwidth / 2.0f);
+        m_lowpass.create(301, m_audioSampleRate,  m_settings.m_rfBandwidth / 2.0f);
         DSBFilter->create_dsb_filter((2.0f * settings.m_rfBandwidth) / (float) m_audioSampleRate);
         m_settingsMutex.unlock();
 
diff --git a/plugins/channelrx/demodam/amdemod.h b/plugins/channelrx/demodam/amdemod.h
index 9baba749a..1b2d2f764 100644
--- a/plugins/channelrx/demodam/amdemod.h
+++ b/plugins/channelrx/demodam/amdemod.h
@@ -207,6 +207,7 @@ private:
 	MovingAverageUtil<Real, double, 16> m_movingAverage;
 	SimpleAGC<4800> m_volumeAGC;
     Bandpass<Real> m_bandpass;
+    Lowpass<Real> m_lowpass;
     Lowpass<std::complex<float> > m_pllFilt;
     PhaseLockComplex m_pll;
     fftfilt* DSBFilter;