From 4d273d8a1373ff571ff2d6dd977905672fb842cd Mon Sep 17 00:00:00 2001
From: f4exb <f4exb06@gmail.com>
Date: Fri, 28 Oct 2016 03:18:24 +0200
Subject: [PATCH] Tx ph.2: use a specialized interpolator similar to the
 decimator derived from the ancient interpolator

---
 plugins/channeltx/modam/ammod.cpp           | 25 +++++++++++++++------
 plugins/samplesink/filesink/filesinkgui.cpp |  4 ++--
 plugins/samplesink/filesink/filesinkgui.h   |  2 +-
 sdrbase/dsp/interpolator.h                  | 25 ++++++++++-----------
 4 files changed, 33 insertions(+), 23 deletions(-)

diff --git a/plugins/channeltx/modam/ammod.cpp b/plugins/channeltx/modam/ammod.cpp
index 3dc498c58..1d6ab3fe0 100644
--- a/plugins/channeltx/modam/ammod.cpp
+++ b/plugins/channeltx/modam/ammod.cpp
@@ -65,17 +65,28 @@ void AMMod::pull(Sample& sample)
 {
 	Complex ci;
 
-	m_interpolator.interpolate(&m_interpolatorDistanceRemain, m_modSample, &m_interpolatorConsumed, &ci);
-	m_interpolatorDistanceRemain += m_interpolatorDistance;
+//  Resampler used for interpolation only
+//	m_interpolator.resample(&m_interpolatorDistanceRemain, m_modSample, &m_interpolatorConsumed, &ci);
+//	m_interpolatorDistanceRemain += m_interpolatorDistance;
+//
+//	if (m_interpolatorConsumed)
+//	{
+//		Real t = m_toneNco.next();
+//		m_modSample.real(((t+1.0f) * m_running.m_modFactor * 16384.0f)); // modulate and scale zero frequency carrier
+//		m_modSample.imag(0.0f);
+//		m_interpolatorConsumed = false;
+//	}
 
-	if (m_interpolatorConsumed)
+//  Specialized interpolator
+	if (m_interpolator.interpolate(&m_interpolatorDistanceRemain, m_modSample, &ci))
 	{
-		Real t = m_toneNco.next();
-		m_modSample.real(((t+1.0f) * m_running.m_modFactor * 16384.0f)); // modulate and scale zero frequency carrier
-		m_modSample.imag(0.0f);
-		m_interpolatorConsumed = false;
+        Real t = m_toneNco.next();
+        m_modSample.real(((t+1.0f) * m_running.m_modFactor * 16384.0f)); // modulate and scale zero frequency carrier
+        m_modSample.imag(0.0f);
 	}
 
+    m_interpolatorDistanceRemain += m_interpolatorDistance;
+
     ci *= m_carrierNco.nextIQ(); // shift to carrier frequency
 
     Real magsq = ci.real() * ci.real() + ci.imag() * ci.imag();
diff --git a/plugins/samplesink/filesink/filesinkgui.cpp b/plugins/samplesink/filesink/filesinkgui.cpp
index 5effdce5a..ba512a33e 100644
--- a/plugins/samplesink/filesink/filesinkgui.cpp
+++ b/plugins/samplesink/filesink/filesinkgui.cpp
@@ -327,8 +327,8 @@ void FileSinkGui::tick()
 	}
 }
 
-unsigned int FileSinkSampleRates::m_rates[] = {48, 60, 64, 80};
-unsigned int FileSinkSampleRates::m_nb_rates = 4;
+unsigned int FileSinkSampleRates::m_rates[] = {48, 60, 60, 64, 72};
+unsigned int FileSinkSampleRates::m_nb_rates = 5;
 
 unsigned int FileSinkSampleRates::getRate(unsigned int rate_index)
 {
diff --git a/plugins/samplesink/filesink/filesinkgui.h b/plugins/samplesink/filesink/filesinkgui.h
index fbe152598..575b1761b 100644
--- a/plugins/samplesink/filesink/filesinkgui.h
+++ b/plugins/samplesink/filesink/filesinkgui.h
@@ -93,7 +93,7 @@ public:
 	static unsigned int getRateIndex(unsigned int rate);
 	static unsigned int getNbRates();
 private:
-	static unsigned int m_rates[4];
+	static unsigned int m_rates[5];
 	static unsigned int m_nb_rates;
 };
 
diff --git a/sdrbase/dsp/interpolator.h b/sdrbase/dsp/interpolator.h
index 3021d11c1..24f7e1b36 100644
--- a/sdrbase/dsp/interpolator.h
+++ b/sdrbase/dsp/interpolator.h
@@ -35,27 +35,26 @@ public:
 		return true;
 	}
 
-	// interpolation works nearly the same way // TODO: remove when original is used
+	// interpolation simplified from the generalized resampler
 	bool interpolate(Real *distance, const Complex& next, Complex* result)
 	{
-        *distance -= 1.0;
+	    bool consumed = false;
 
-        if (*distance < 1.0) // use sample
+        if (*distance >= 1.0)
         {
             advanceFilter(next);
-            doInterpolate((int) floor(*distance * (Real)m_phaseSteps), result);
-            return true;  // need new input sample and increment distance
-        }
-        else // use zero
-        {
-            advanceFilter();
-            doInterpolate((int) floor(*distance * (Real)m_phaseSteps), result);
-            return false; // input sample was not used and do not increment distance
+            *distance -= 1.0;
+            consumed = true;
         }
+
+        doInterpolate((int)floor(*distance * (Real)m_phaseSteps), result);
+
+        return consumed;
 	}
 
-	// original interpolator
-	bool interpolate(Real* distance, const Complex& next, bool* consumed, Complex* result)
+	// original interpolator which is actually an arbitrary rational resampler P/Q for any positive P, Q
+	// sampling frequency must be the highest of the two
+	bool resample(Real* distance, const Complex& next, bool* consumed, Complex* result)
 	{
 		while(*distance >= 1.0)
 		{