From cd347bca4ff1756ecdb4f1bbeee4bb6001393a1e Mon Sep 17 00:00:00 2001
From: f4exb <f4exb06@gmail.com>
Date: Fri, 28 Oct 2016 05:08:53 +0200
Subject: [PATCH] Allow interpolation in AM demodulator i.e. input sample rate
 lower than audio rate

---
 plugins/channelrx/demodam/amdemod.cpp | 82 +++++----------------------
 plugins/channelrx/demodam/amdemod.h   | 70 +++++++++++++++++++++++
 2 files changed, 85 insertions(+), 67 deletions(-)

diff --git a/plugins/channelrx/demodam/amdemod.cpp b/plugins/channelrx/demodam/amdemod.cpp
index 0cbced721..76cb810dc 100644
--- a/plugins/channelrx/demodam/amdemod.cpp
+++ b/plugins/channelrx/demodam/amdemod.cpp
@@ -77,76 +77,24 @@ void AMDemod::feed(const SampleVector::const_iterator& begin, const SampleVector
 		Complex c(it->real(), it->imag());
 		c *= m_nco.nextIQ();
 
-		if (m_interpolator.decimate(&m_interpolatorDistanceRemain, c, &ci))
+		if (m_interpolatorDistance < 1.0f) // interpolate
 		{
-			Real magsq = ci.real() * ci.real() + ci.imag() * ci.imag();
-			magsq /= (1<<30);
-			m_movingAverage.feed(magsq);
-			m_magsq = m_movingAverage.average();
+            processOneSample(ci);
 
-			if (m_magsq >= m_squelchLevel)
-			{
-				if (m_squelchCount <= m_running.m_audioSampleRate / 10)
-				{
-					m_squelchCount++;
-				}
-			}
-			else
-			{
-				if (m_squelchCount > 1)
-				{
-					m_squelchCount -= 2;
-				}
-			}
+		    while (m_interpolator.interpolate(&m_interpolatorDistanceRemain, c, &ci))
+            {
+                processOneSample(ci);
+            }
 
-			qint16 sample;
-
-			if ((m_squelchCount >= m_running.m_audioSampleRate / 20) && !m_running.m_audioMute)
-			{
-				Real demod = sqrt(magsq);
-
-				demod = m_lowpass.filter(demod);
-
-				if (demod < -1)
-				{
-					demod = -1;
-				}
-				else if (demod > 1)
-				{
-					demod = 1;
-				}
-
-				m_volumeAGC.feed(demod);
-
-				Real attack = (m_squelchCount - (m_running.m_audioSampleRate / 20)) / (Real) (m_running.m_audioSampleRate / 20);
-				demod *= ((0.003 * attack) / m_volumeAGC.getValue());
-				demod *= m_running.m_volume;
-				sample = demod * 32700 * 16;
-				m_squelchOpen = true;
-			}
-			else
-			{
-				sample = 0;
-				m_squelchOpen = false;
-			}
-
-			m_audioBuffer[m_audioBufferFill].l = sample;
-			m_audioBuffer[m_audioBufferFill].r = sample;
-			++m_audioBufferFill;
-
-			if (m_audioBufferFill >= m_audioBuffer.size())
-			{
-				uint res = m_audioFifo.write((const quint8*)&m_audioBuffer[0], m_audioBufferFill, 10);
-
-				if (res != m_audioBufferFill)
-				{
-					qDebug("AMDemod::feed: %u/%u audio samples written", res, m_audioBufferFill);
-				}
-
-				m_audioBufferFill = 0;
-			}
-
-			m_interpolatorDistanceRemain += m_interpolatorDistance;
+            m_interpolatorDistanceRemain += m_interpolatorDistance;
+		}
+		else // decimate
+		{
+	        if (m_interpolator.decimate(&m_interpolatorDistanceRemain, c, &ci))
+	        {
+	            processOneSample(ci);
+	            m_interpolatorDistanceRemain += m_interpolatorDistance;
+	        }
 		}
 	}
 
diff --git a/plugins/channelrx/demodam/amdemod.h b/plugins/channelrx/demodam/amdemod.h
index ccc2cfc35..3f634ee60 100644
--- a/plugins/channelrx/demodam/amdemod.h
+++ b/plugins/channelrx/demodam/amdemod.h
@@ -134,6 +134,76 @@ private:
 	QMutex m_settingsMutex;
 
 	void apply();
+
+	void processOneSample(Complex &ci)
+	{
+        Real magsq = ci.real() * ci.real() + ci.imag() * ci.imag();
+        magsq /= (1<<30);
+        m_movingAverage.feed(magsq);
+        m_magsq = m_movingAverage.average();
+
+        if (m_magsq >= m_squelchLevel)
+        {
+            if (m_squelchCount <= m_running.m_audioSampleRate / 10)
+            {
+                m_squelchCount++;
+            }
+        }
+        else
+        {
+            if (m_squelchCount > 1)
+            {
+                m_squelchCount -= 2;
+            }
+        }
+
+        qint16 sample;
+
+        if ((m_squelchCount >= m_running.m_audioSampleRate / 20) && !m_running.m_audioMute)
+        {
+            Real demod = sqrt(magsq);
+
+            demod = m_lowpass.filter(demod);
+
+            if (demod < -1)
+            {
+                demod = -1;
+            }
+            else if (demod > 1)
+            {
+                demod = 1;
+            }
+
+            m_volumeAGC.feed(demod);
+
+            Real attack = (m_squelchCount - (m_running.m_audioSampleRate / 20)) / (Real) (m_running.m_audioSampleRate / 20);
+            demod *= ((0.003 * attack) / m_volumeAGC.getValue());
+            demod *= m_running.m_volume;
+            sample = demod * 32700 * 16;
+            m_squelchOpen = true;
+        }
+        else
+        {
+            sample = 0;
+            m_squelchOpen = false;
+        }
+
+        m_audioBuffer[m_audioBufferFill].l = sample;
+        m_audioBuffer[m_audioBufferFill].r = sample;
+        ++m_audioBufferFill;
+
+        if (m_audioBufferFill >= m_audioBuffer.size())
+        {
+            uint res = m_audioFifo.write((const quint8*)&m_audioBuffer[0], m_audioBufferFill, 10);
+
+            if (res != m_audioBufferFill)
+            {
+                qDebug("AMDemod::feed: %u/%u audio samples written", res, m_audioBufferFill);
+            }
+
+            m_audioBufferFill = 0;
+        }
+	}
 };
 
 #endif // INCLUDE_AMDEMOD_H