Merge pull request #153 from F4FXL/TranscodingTweaks

Transcoding tweaks

ambed/cagc.cpp

@@ -0,0 +1,94 @@
+//
+//  cagc.cpp
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 28/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// Geoffrey Merck F4FXL / KC3FRA AGC code borrowed from Liquid DSP
+// Only took the parts we need qnd recoeded it to be close the XLX coding style
+// https://github.com/jgaeddert/liquid-dsp/blob/master/src/agc/src/agc.c
+
+#include <math.h>
+#include "cagc.h"
+#include "main.h"
+
+////////////////////////////////////////////////////////////////////////////////////////
+// constructor
+
+CAGC::CAGC(float initialLeveldB)
+{
+    // set internal gain appropriately
+    m_Gain = pow(10.0f, initialLeveldB/20.0f);
+    //+- 10dB Margin, TODO Move margin to constant
+    m_GainMax = pow(10.0f, (initialLeveldB + AGC_CLAMPING)/20.0f);
+    m_GainMin = pow(10.0f, (initialLeveldB - AGC_CLAMPING)/20.0f);
+                        
+    m_EnergyPrime = 1.0f;
+
+    // We do not target full scale to avoid stauration
+    m_targetEnergy = 32767.0f * pow(10.0f, (initialLeveldB - 25.0)/20.0f);//25 dB below saturation as stated in docs
+                                                                        //we also substract our target gain
+
+    //this is the time constant of our AGC...
+    m_Bandwidth = 1e-2f;//TODO : Move to parameter ?    
+    m_Alpha = m_Bandwidth;  
+}
+
+////////////////////////////////////////////////////////////////////////////////////////
+// get
+
+float CAGC::GetGain()
+{
+    return 20.0f*log10(m_Gain);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////
+// process
+
+inline void CAGC::ProcessSampleBlock(uint8* voice, int length) 
+{
+    for(int i = 0; i < length; i += 2)
+    {
+        float input = (float)(short)MAKEWORD(voice[i+1], voice[i]);
+        //apply AGC
+        // apply gain to input sample
+        float output = input * m_Gain;
+
+        // compute output signal energy, scaled to 0 to 1
+        float instantEnergy = abs(output) / m_targetEnergy;
+
+        // smooth energy estimate using single-pole low-pass filter
+        m_EnergyPrime = (1.0f - m_Alpha) * m_EnergyPrime + m_Alpha * instantEnergy;
+
+        // update gain according to output energy
+        if (m_EnergyPrime > 1e-6f)
+            m_Gain *= exp( -0.5f * m_Alpha * log(m_EnergyPrime) ); 
+
+        // clamp gain
+        if (m_Gain > m_GainMax)
+            m_Gain = m_GainMax;
+        else if(m_Gain < m_GainMin)
+            m_Gain = m_GainMin;
+
+        //write processed sample back
+        voice[i] = HIBYTE((short)output);
+        voice[i+1] = LOBYTE((short)output);
+    }
+}

ambed/cagc.h

@@ -0,0 +1,56 @@
+//
+//  cagc.h
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 26/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// Geoffrey Merck F4FXL / KC3FRA AGC code largely inspired by Liquid DSP
+// Only took the parts we need qnd recoeded it to be close the XLX coding style
+// https://github.com/jgaeddert/liquid-dsp/blob/master/src/agc/src/agc.c 
+
+#ifndef cagc_h
+#define cagc_h
+
+#include "csampleblockprocessor.h"
+
+class CAGC : CSampleBlockProcessor
+{
+public:
+    //Constructor
+    CAGC(float initialLeveldB);
+
+    //methods
+    void ProcessSampleBlock(uint8* voice, int length) ;
+    float GetGain();//gets current gain 
+    
+private:
+    float m_Gain;            // current gain value
+    float m_GainMax, m_GainMin;       //gain clamping
+    float m_targetEnergy;        // scale value for target energy
+
+    // gain control loop filter parameters
+    float m_Bandwidth;    // bandwidth-time constant
+    float m_Alpha;        // feed-back gain
+
+    // signal level estimate
+    float m_EnergyPrime;     // filtered output signal energy estimate
+};
+
+#endif /* cgc_h */

ambed/cfirfilter.cpp

@@ -0,0 +1,75 @@
+//
+//  cfirfilter.cpp
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 26/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// FIRFilter by Geoffrey Merck F4FXL / KC3FRA
+
+#include "cfirfilter.h"
+#include <string.h>
+
+CFIRFilter::CFIRFilter(const float* taps, int tapsLength)
+{
+    m_taps = new float[tapsLength];
+    m_buffer = new float[tapsLength];
+    m_tapsLength = tapsLength;
+
+    ::memcpy(m_taps, taps, tapsLength * sizeof(float));
+    ::memset(m_buffer, 0, tapsLength * sizeof(float));
+    m_currentBufferPosition = 0;
+}
+
+CFIRFilter::~CFIRFilter()
+{
+    delete[] m_taps;
+    delete[] m_buffer;
+}
+
+inline void CFIRFilter::ProcessSampleBlock(uint8* voice, int length)
+{
+    for(int i = 0; i < length; i += 2)
+    {
+        float input = (float)(short)MAKEWORD(voice[i+1], voice[i]);
+        float output = 0.0f;
+        int iTaps = 0;
+
+        // Buffer latest sample into delay line
+        m_buffer[m_currentBufferPosition] = input;
+
+        for(int i = m_currentBufferPosition; i >= 0; i--)
+        {
+            output += m_taps[iTaps++] * m_buffer[i];
+        }
+
+        for(int i = m_tapsLength - 1; i > m_currentBufferPosition; i--)
+        {
+            output += m_taps[iTaps++] * m_buffer[i];
+        }
+        
+        m_currentBufferPosition = (m_currentBufferPosition + 1) % m_tapsLength;
+
+        //write processed sample back
+        voice[i] = HIBYTE((short)output);
+        voice[i+1] = LOBYTE((short)output);
+    }
+}
+
+

ambed/cfirfilter.h

@@ -0,0 +1,51 @@
+//
+//  cfirfilter.h
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 26/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// FIRFilter by Geoffrey Merck F4FXL / KC3FRA
+
+#ifndef cfirfilter_h
+#define cfirfilter_h
+
+#include "csampleblockprocessor.h"
+
+class CFIRFilter : CSampleBlockProcessor
+{
+public :
+    //Constructor
+    CFIRFilter(const float* taps, int tapsLength);
+
+    // Destructor
+    ~CFIRFilter();
+
+    // Processing
+    void ProcessSampleBlock(uint8* voice, int length);
+
+private:
+    float* m_taps;
+    int m_tapsLength;
+    float* m_buffer;
+    int m_currentBufferPosition;
+};
+
+#endif //cfirfilter_h
+

ambed/cfixedgain.cpp

@@ -0,0 +1,53 @@
+//
+//  cfixedgain.cpp
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 28/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// Geoffrey Merck F4FXL / KC3FRA AGC
+
+#include "cfixedgain.h"
+#include <math.h>
+
+////////////////////////////////////////////////////////////////////////////////////////
+// constructor
+
+CFixedGain::CFixedGain(float gaindB)
+{
+    m_gaindB = gaindB;
+    m_gainLinear = pow(10.0f, m_gaindB/20.0f);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////
+// processing
+ 
+inline void CFixedGain::ProcessSampleBlock(uint8* voice, int length)
+{
+    for(int i = 0; i < length; i += 2)
+    {
+        float input = (float)(short)MAKEWORD(voice[i+1], voice[i]);
+        //apply gain
+        float output = input * m_gainLinear;
+
+        //write processed sample back
+        voice[i] = HIBYTE((short)output);
+        voice[i+1] = LOBYTE((short)output);
+    }
+}

ambed/cfixedgain.h

@@ -0,0 +1,45 @@
+//
+//  cfixedgain.h
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 26/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// Geoffrey Merck F4FXL / KC3FRA
+
+#ifndef cfixedgain_h
+#define cfixedgain_h
+
+#include "csampleblockprocessor.h"
+
+class CFixedGain : CSampleBlockProcessor
+{
+public:
+    //Constructor
+    CFixedGain(float gaindB);
+
+    //processing
+    void ProcessSampleBlock(uint8* voice, int length);
+
+private:
+    float m_gaindB; //gain in dB
+    float m_gainLinear; //linearized gain
+};
+
+#endif /* cfixedgain_h */

ambed/csampleblockprocessor.h

@@ -0,0 +1,38 @@
+//
+//  csampleprocessor.h
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 26/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// Geoffrey Merck F4FXL / KC3FRA
+
+#ifndef csamplebloclprocessor_h
+#define csamplebloclprocessor_h
+
+#include "main.h"
+
+class CSampleBlockProcessor
+{
+public:
+    //processing
+    virtual void ProcessSampleBlock(uint8* voice, int length) = 0;
+};
+
+#endif /* csampleprocessor_h */

ambed/csignalprocessor.cpp

@@ -0,0 +1,94 @@
+//
+//  cagc.cpp
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 28/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// Geoffrey Merck F4FXL / KC3FRA AGC
+
+#include "main.h"
+#include "csignalprocessor.h"
+
+#if USE_AGC == 1
+#include "cagc.h"
+#else
+#include "cfixedgain.h"
+#endif
+
+#if USE_BANDPASSFILTER == 1
+#include "cfirfilter.h"
+#endif
+
+////////////////////////////////////////////////////////////////////////////////////////
+// constructor
+
+CSignalProcessor::CSignalProcessor(float gaindB)
+{
+#if USE_BANDPASSFILTER
+    m_sampleProcessors.push_back((CSampleBlockProcessor*)new CFIRFilter(FILTER_TAPS, FILTER_TAPS_LENGTH));
+#endif
+#if USE_AGC == 1
+    m_sampleProcessors.push_back((CSampleBlockProcessor*)new CAGC(gaindB));
+#else
+    m_sampleProcessors.push_back((CSampleBlockProcessor*)new CFixedGain(gaindB));
+#endif
+}
+
+////////////////////////////////////////////////////////////////////////////////////////
+// destructor
+
+CSignalProcessor::~CSignalProcessor()
+{
+    for(int i = 0; i < m_sampleProcessors.size(); i++)
+    {
+        delete m_sampleProcessors[i];
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////////////
+// processing
+
+void CSignalProcessor::Process(uint8* voice, int length)
+{
+    /*float sample;
+    int j;*/
+    auto processorsSize = m_sampleProcessors.size();
+
+    for(int j = 0; j < processorsSize; j++)
+    {
+        m_sampleProcessors[j]->ProcessSampleBlock(voice, length);
+    }
+
+    /*for(int i = 0; i < length; i += 2)
+    {
+        //Get the sample
+        sample = (float)(short)MAKEWORD(voice[i+1], voice[i]);
+
+        for(j = 0; j < processorsSize; j++)
+        {
+            sample = m_sampleProcessors[j]->ProcessSample(sample);
+        }
+
+        //write processed sample back
+        voice[i] = HIBYTE((short)sample);
+        voice[i+1] = LOBYTE((short)sample);
+    }*/
+}

ambed/csignalprocessor.h

@@ -0,0 +1,48 @@
+//
+//  csignalprocessor.h
+//  ambed
+//
+//  Created by Jean-Luc Deltombe (LX3JL) on 26/04/2017.
+//  Copyright © 2015 Jean-Luc Deltombe (LX3JL). All rights reserved.
+//
+// ----------------------------------------------------------------------------
+//    This file is part of ambed.
+//
+//    xlxd 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, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    xlxd 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 for more details.
+//
+//    You should have received a copy of the GNU General Public License
+//    along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
+// ----------------------------------------------------------------------------
+// Geoffrey Merck F4FXL / KC3FRA
+
+#ifndef csignalprocessor_h
+#define csignalprocessor_h
+
+#include <vector>
+#include "csampleblockprocessor.h"
+
+class CSignalProcessor
+{
+public:
+    //Constructor
+    CSignalProcessor(float gaindB);
+
+    //Destructor
+    ~CSignalProcessor();
+
+    //Processing
+    void Process(uint8* voice, int length);
+
+private:
+    std::vector<CSampleBlockProcessor *> m_sampleProcessors;
+};
+
+#endif /* csignalprocessor_h */

ambed/cusb3xxxinterface.cpp

@@ -152,7 +152,7 @@ void CUsb3xxxInterface::Task(void)
             {
                 Queue = Channel->GetVoiceQueue();
                 CVoicePacket *clone = new CVoicePacket(VoicePacket);
-                clone->ApplyGain(Channel->GetSpeechGain());
+                Channel->ProcessSignal(*clone);
                 Queue->push(clone);
                 Channel->ReleaseVoiceQueue();
             }

ambed/cvocodecchannel.cpp

@@ -27,7 +27,6 @@
 #include "cvocodecchannel.h"
 #include "cvocodecinterface.h"
 
-
 ////////////////////////////////////////////////////////////////////////////////////////
 // constructor
 
@@ -39,6 +38,7 @@ CVocodecChannel::CVocodecChannel(CVocodecInterface *InterfaceIn, int iChIn, CVoc
     m_InterfaceOut = InterfaceOut;
     m_iChannelOut = iChOut;
     m_iSpeechGain = iSpeechGain;
+    m_signalProcessor = new CSignalProcessor((float)m_iSpeechGain);
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////
@@ -47,6 +47,7 @@ CVocodecChannel::CVocodecChannel(CVocodecInterface *InterfaceIn, int iChIn, CVoc
 CVocodecChannel::~CVocodecChannel()
 {
     PurgeAllQueues();
+    delete m_signalProcessor;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////
@@ -92,6 +93,15 @@ uint8 CVocodecChannel::GetCodecOut(void) const
     return m_InterfaceOut->GetChannelCodec(m_iChannelOut);
 }
 
+////////////////////////////////////////////////////////////////////////////////////////
+// processing
+
+void CVocodecChannel::ProcessSignal(CVoicePacket& voicePacket)
+{
+    m_signalProcessor->Process(voicePacket.GetVoice(), voicePacket.GetVoiceSize());
+}
+
+
 ////////////////////////////////////////////////////////////////////////////////////////
 // queues helpers
 

ambed/cvocodecchannel.h

@@ -27,6 +27,8 @@
 #define cvocodecchannel_h
 
 #include "cpacketqueue.h"
+#include "csignalprocessor.h"
+#include "cvoicepacket.h"
 
 ////////////////////////////////////////////////////////////////////////////////////////
 // class
@@ -54,6 +56,9 @@ public:
     int   GetChannelOut(void) const         { return m_iChannelOut; }
     int   GetSpeechGain(void) const         { return m_iSpeechGain; }
     
+    //Processing
+    void ProcessSignal(CVoicePacket& voicePacket);
+    
     // interfaces
     bool IsInterfaceIn(const CVocodecInterface *interface)      { return (interface == m_InterfaceIn); }
     bool IsInterfaceOut(const CVocodecInterface *interface)     { return (interface == m_InterfaceOut); }
@@ -92,6 +97,8 @@ protected:
     // settings
     int                 m_iSpeechGain;
     
+private:
+    CSignalProcessor* m_signalProcessor;
 };
 
 ////////////////////////////////////////////////////////////////////////////////////////

ambed/cvoicepacket.cpp

@@ -69,18 +69,3 @@ void CVoicePacket::SetVoice(const uint8 *voice, int size)
     ::memcpy(m_uiVoice, voice, m_iSize);
 }
 
-
-////////////////////////////////////////////////////////////////////////////////////////
-// gain
-
-void CVoicePacket::ApplyGain(int dB)
-{
-    float mult = pow(10, dB/20.0);
-    for ( int i = 0; i < m_iSize; i += 2 )
-    {
-        float smp = (float)(short)MAKEWORD(m_uiVoice[i+1], m_uiVoice[i]);
-        smp *= mult;
-        m_uiVoice[i] = HIBYTE((short)smp);
-        m_uiVoice[i+1] = LOBYTE((short)smp);
-    }
-}

ambed/cvoicepacket.h

@@ -58,9 +58,6 @@ public:
     // set
     void   SetVoice(const uint8 *, int);
     
-    // gain
-    void  ApplyGain(int);
-    
 protected:
     // data
     int     m_iSize;

ambed/main.h

@@ -68,9 +68,14 @@
 #define CODEC_AMBE2PLUS                 2
 
 // Transcoding speech gains
-#define CODECGAIN_AMBEPLUS              -10                                  // in dB
+#define CODECGAIN_AMBEPLUS              -10                                 // in dB
 #define CODECGAIN_AMBE2PLUS             +10                                 // in dB
 
+// Transcoding Tweaks
+#define USE_AGC                         0
+#define AGC_CLAMPING                    3                                   //clamps the AGC gain to +- this value
+#define USE_BANDPASSFILTER              1
+
 // Timeouts -----------------------------------------------------
 #define STREAM_ACTIVITY_TIMEOUT         3                                   // in seconds
 
@@ -96,6 +101,39 @@ typedef unsigned int            uint;
 #define LOWORD(dw)				((uint16)(uint32)(dw & 0x0000FFFF))
 #define HIWORD(dw)				((uint16)((((uint32)(dw)) >> 16) & 0xFFFF))
 
+////////////////////////////////////////////////////////////////////////////////////////
+// FIR Filter coefficients computed to be the closest to the recommended filter in 
+// Documentation
+//
+// Following GNU Octave script was used
+/*
+pkg load signal;
+fsamp = 8000;
+fcuts = [300 400 3000 3400];
+mags = [0 1 0];
+devs = [0.2 1 0.2];
+
+[n,Wn,beta,ftype] = kaiserord(fcuts,mags,devs,fsamp);
+n = n + rem(n,2);
+hh = fir1(n,Wn,ftype,kaiser(n+1,beta),'noscale');
+
+freqz(hh);
+[H,f] = freqz(hh,1,1024,fsamp);
+plot(f,abs(H))
+disp(hh);
+grid
+*/
+
+#if USE_BANDPASSFILTER == 1
+
+const float FILTER_TAPS[] {
+-0.05063341f, -0.00060337f, -0.08892498f, -0.02026701f, -0.05940750f, -0.10977641f,  0.03244024f, -0.22304499f,
+0.11452865f,  0.72500000f,  0.11452865f, -0.22304499f,  0.03244024f, -0.10977641f, -0.05940750f, -0.02026701f,
+-0.08892498f, -0.00060337f, -0.05063341f };
+#define FILTER_TAPS_LENGTH          19
+
+#endif
+
 ////////////////////////////////////////////////////////////////////////////////////////
 // global objects