NFMDemodSink: Proper audio scaling to 16-bit

plugins/channelrx/demodnfm/nfmdemodsink.cpp

@@ -27,6 +27,7 @@
 #include "dsp/dspengine.h"
 #include "dsp/dspcommands.h"
 #include "dsp/devicesamplemimo.h"
+#include "dsp/misc.h"
 #include "device/deviceapi.h"
 
 #include "nfmdemodreport.h"
@@ -58,6 +59,7 @@ NFMDemodSink::NFMDemodSink() :
 {
 	m_agcLevel = 1.0;
     m_audioBuffer.resize(1<<16);
+    m_phaseDiscri.setFMScaling(1.0f);
 
 	applySettings(m_settings, true);
     applyChannelSettings(m_channelSampleRate, m_channelFrequencyOffset, true);
@@ -174,9 +176,11 @@ void NFMDemodSink::processOneSample(Complex &ci)
         if (!m_settings.m_audioMute && (m_settings.m_ctcssOn && m_ctcssIndexSelected == ctcssIndex || m_ctcssIndexSelected == 0))
         {
             Real audioSample = m_squelchDelayLine.readBack(m_squelchGate);
+            Q_ASSERT(audioSample >= -1.0f && audioSample <= 1.0f);
             audioSample = m_settings.m_highPass ? m_bandpass.filter(audioSample) : m_lowpass.filter(audioSample);
-            audioSample *= m_settings.m_volume * m_filterTaps;
-            sample = std::lrint(audioSample);
+
+            audioSample *= m_settings.m_volume * std::numeric_limits<int16_t>::max();
+            sample = clamp<float>(std::rint(audioSample), std::numeric_limits<int16_t>::lowest(), std::numeric_limits<int16_t>::max());
         }
     }
 
@@ -258,11 +262,6 @@ void NFMDemodSink::applySettings(const NFMDemodSettings& settings, bool force)
         m_interpolatorDistance =  (Real) m_channelSampleRate / (Real) m_audioSampleRate;
     }
 
-    if ((settings.m_fmDeviation != m_settings.m_fmDeviation) || force)
-    {
-        m_phaseDiscri.setFMScaling((8.0f*m_audioSampleRate) / static_cast<float>(settings.m_fmDeviation)); // integrate 4x factor
-    }
-
     if ((settings.m_afBandwidth != m_settings.m_afBandwidth) || force)
     {
         m_bandpass.create(m_filterTaps, m_audioSampleRate, 300.0, settings.m_afBandwidth);
@@ -324,7 +323,6 @@ void NFMDemodSink::applyAudioSampleRate(unsigned int sampleRate)
         m_afSquelch.setCoefficients(sampleRate/2000, 600, sampleRate, 200, 0, afSqTones); // 0.5ms test period, 300ms average span, audio SR, 100ms attack, no decay
     }
 
-    m_phaseDiscri.setFMScaling((8.0f*sampleRate) / static_cast<float>(m_settings.m_fmDeviation)); // integrate 4x factor
     m_audioFifo.setSize(sampleRate);
     m_squelchDelayLine.resize(sampleRate/2);
     m_interpolatorDistanceRemain = 0;

plugins/channelrx/demodnfm/nfmdemodsink.h

@@ -139,39 +139,6 @@ private:
 
     void processOneSample(Complex &ci);
     MessageQueue *getMessageQueueToGUI() { return m_messageQueueToGUI; }
-
-    inline float arctan2(Real y, Real x)
-    {
-        Real coeff_1 = M_PI / 4;
-        Real coeff_2 = 3 * coeff_1;
-        Real abs_y = fabs(y) + 1e-10;      // kludge to prevent 0/0 condition
-        Real angle;
-        if( x>= 0) {
-            Real r = (x - abs_y) / (x + abs_y);
-            angle = coeff_1 - coeff_1 * r;
-        } else {
-            Real r = (x + abs_y) / (abs_y - x);
-            angle = coeff_2 - coeff_1 * r;
-        }
-        if(y < 0) {
-            return(-angle);
-        } else {
-            return(angle);
-        }
-    }
-
-    inline Real angleDist(Real a, Real b)
-    {
-        Real dist = b - a;
-
-        while(dist <= M_PI)
-            dist += 2 * M_PI;
-        while(dist >= M_PI)
-            dist -= 2 * M_PI;
-
-        return dist;
-    }
-
 };
 
 #endif // INCLUDE_NFMDEMODSINK_H

sdrbase/dsp/firfilter.cpp

@@ -52,6 +52,19 @@ void generateLowPassFilter(int nTaps, double sampleRate, double cutoff, std::vec
         int n = i - (nTaps - 1) / 2;
         taps[i] *= 0.42 + 0.5 * cos((2.0 * M_PI * n) / nTaps) + 0.08 * cos((4.0 * M_PI * n) / nTaps);
     }
+
+    Real sum = 0;
+    size_t i;
+
+    for (i = 0; i < taps.size() - 1; ++i) {
+        sum += taps[i] * 2.0;
+    }
+
+    sum += taps[i];
+
+    for (i = 0; i < taps.size(); ++i) {
+        taps[i] /= sum;
+    }
 }
 
 }

sdrbase/dsp/firfilter.h

@@ -20,6 +20,7 @@
 
 #include <cmath>
 #include "dsp/dsptypes.h"
+#include "dsp/misc.h"
 #include "export.h"
 
 namespace FirFilterGenerators
@@ -74,22 +75,6 @@ protected:
         }
     }
 
-    void normalize(Real sum_fix = 0.0)
-    {
-        Real sum = 0;
-        size_t i;
-
-        for (i = 0; i < m_taps.size() - 1; ++i) {
-            sum += m_taps[i] * 2.0;
-        }
-
-        sum += m_taps[i] + sum_fix;
-
-        for (i = 0; i < m_taps.size(); ++i) {
-            m_taps[i] /= sum;
-        }
-    }
-
 protected:
     std::vector<Real> m_taps;
     std::vector<Type> m_samples;
@@ -104,7 +89,6 @@ public:
     {
         this->init(nTaps);
         FirFilterGenerators::generateLowPassFilter(nTaps, sampleRate, cutoff, this->m_taps);
-        this->normalize();
     }
 };
 
@@ -129,7 +113,6 @@ struct Bandpass : public FirFilter<T>
         }
 
         this->m_taps[this->m_taps.size() - 1] += 1;
-        this->normalize(-1.0);
     }
 };
 
@@ -146,6 +129,5 @@ struct Highpass : public FirFilter<T>
         }
 
         this->m_taps[this->m_taps.size() - 1] += 1;
-        this->normalize(-1.0);
     }
 };

sdrbase/dsp/misc.h

@@ -36,7 +36,8 @@ inline float cosc(float x)
 	return (fabs(x) < 1e-10) ? 0.0 : ((1.0 - cos(M_PI * x)) / (M_PI * x));
 }
 
-inline float clamp(float x, float min, float max)
+template<typename T>
+inline T clamp(T x, T min, T max)
 {
 	return (x < min) ? min : ((x > max) ? max : x);
 }