DSD demod: highpass filtering for audio (1)

plugins/channelrx/demoddsd/dsddemodgui.ui

@@ -825,6 +825,20 @@
         </property>
        </widget>
       </item>
+      <item>
+       <widget class="ButtonSwitch" name="highPassFilter">
+        <property name="toolTip">
+         <string>Toggle audio high pass filter for mbelib (&gt;300 Hz)</string>
+        </property>
+        <property name="text">
+         <string/>
+        </property>
+        <property name="icon">
+         <iconset resource="../../../sdrgui/resources/res.qrc">
+          <normaloff>:/filter_highpass.png</normaloff>:/filter_highpass.png</iconset>
+        </property>
+       </widget>
+      </item>
       <item>
        <widget class="QToolButton" name="audioMute">
         <property name="toolTip">

plugins/channelrx/demoddsd/dsddemodsettings.cpp

@@ -52,6 +52,7 @@ void DSDDemodSettings::resetToDefaults()
     m_udpPort = 9999;
     m_rgbColor = QColor(0, 255, 255).rgb();
     m_title = "DSD Demodulator";
+    m_highPassFilter = false;
 }
 
 QByteArray DSDDemodSettings::serialize() const
@@ -83,6 +84,7 @@ QByteArray DSDDemodSettings::serialize() const
     }
 
     s.writeString(18, m_title);
+    s.writeBool(19, m_highPassFilter);
 
     return s.final();
 }
@@ -136,6 +138,7 @@ bool DSDDemodSettings::deserialize(const QByteArray& data)
         d.readBool(15, &m_slot2On, false);
         d.readBool(16, &m_tdmaStereo, false);
         d.readString(18, &m_title, "DSD Demodulator");
+        d.readBool(19, &m_highPassFilter, false);
 
         return true;
     }

plugins/channelrx/demoddsd/dsddemodsettings.h

@@ -45,6 +45,7 @@ struct DSDDemodSettings
     quint16 m_udpPort;
     quint32 m_rgbColor;
     QString m_title;
+    bool m_highPassFilter;
 
     Serializable *m_channelMarker;
     Serializable *m_scopeGUI;

sdrbase/CMakeLists.txt

@@ -108,6 +108,7 @@ set(sdrbase_HEADERS
     dsp/filtermbe.h
     dsp/filerecord.h
     dsp/gfft.h
+    dsp/iirfilter.h
     dsp/interpolator.h
     dsp/hbfiltertraits.h
     dsp/inthalfbandfilter.h

sdrbase/dsp/iirfilter.h

@@ -0,0 +1,127 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2017 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 SDRBASE_DSP_IIRFILTER_H_
+#define SDRBASE_DSP_IIRFILTER_H_
+
+#include <stdint.h>
+#include <assert.h>
+
+template <typename Type, uint32_t Order> class IIRFilter
+{
+public:
+    IIRFilter(const Type *a, const Type *b);
+    ~IIRFilter();
+    Type run(Type sample);
+
+private:
+    Type *m_a;
+    Type *m_b;
+    Type *m_x;
+    Type *m_y;
+};
+
+template <typename Type> class IIRFilter<Type, 2>
+{
+public:
+    IIRFilter(const Type *a, const Type *b);
+    ~IIRFilter();
+    Type run(Type sample);
+
+private:
+    Type m_a[3];
+    Type m_b[3];
+    Type m_x[2];
+    Type m_y[2];
+};
+
+template <typename Type, uint32_t Order>
+IIRFilter<Type, Order>::IIRFilter(const Type *a, const Type *b)
+{
+    assert(Order > 1);
+
+    m_a = new Type[Order+1];
+    m_b = new Type[Order+1];
+    m_x = new Type[Order];
+    m_y = new Type[Order];
+
+    memcpy(m_a, a, (Order+1)*sizeof(Type));
+    memcpy(m_b, b, (Order+1)*sizeof(Type));
+
+    for (int i = 0; i < Order; i++)
+    {
+        m_x[i] = 0;
+        m_y[i] = 0;
+    }
+}
+
+template <typename Type, uint32_t Order>
+IIRFilter<Type, Order>::~IIRFilter()
+{
+    delete[] m_y;
+    delete[] m_x;
+    delete[] m_b;
+    delete[] m_a;
+}
+
+template <typename Type, uint32_t Order>
+Type IIRFilter<Type, Order>::run(Type sample)
+{
+    Type y = m_a[0] * sample;
+
+    for (int i = 0; i < Order; i++)
+    {
+        y += m_a[i+1] * m_x[i] + m_b[i+1] * m_y[i];
+    }
+
+    m_x[0] = sample;
+    m_y[0] = y;
+
+    memcpy(&m_x[1], &m_x[0], (Order-1)*sizeof(Type));
+}
+
+template <typename Type>
+IIRFilter<Type, 2>::IIRFilter(const Type *a, const Type *b)
+{
+    m_a[0] = a[0];
+    m_a[1] = a[1];
+    m_a[2] = a[2];
+    m_b[0] = b[0];
+    m_b[1] = b[1];
+    m_b[2] = b[2];
+}
+
+template <typename Type>
+IIRFilter<Type, 2>::~IIRFilter()
+{
+}
+
+template <typename Type>
+Type IIRFilter<Type, 2>::run(Type sample)
+{
+    Type y = m_a[0]*sample + m_a[1]*m_x[0] + m_a[2]*m_x[1] + m_b[1]*m_y[0] + m_b[2]*m_y[1]; // this is y[n]
+
+    m_x[1] = m_x[0];
+    m_x[0] = sample;
+
+    m_y[1] = m_y[0];
+    m_y[0] = y;
+
+    return y;
+}
+
+#endif /* SDRBASE_DSP_IIRFILTER_H_ */

sdrbase/sdrbase.pro

@@ -146,6 +146,7 @@ HEADERS  += audio/audiodeviceinfo.h\
         dsp/filerecord.h\
         dsp/gfft.h\
         dsp/hbfiltertraits.h\
+        dsp/iirfilter.h\
         dsp/interpolator.h\
         dsp/inthalfbandfilter.h\
         dsp/inthalfbandfilterdb.h\

sdrgui/resources/res.qrc

@@ -81,5 +81,6 @@
         <file>choose.png</file>
         <file>clocksource.png</file>
         <file>flip_sidebands.png</file>
+        <file>filter_highpass.png</file>
     </qresource>
 </RCC>