Updates pull request from Roman Tsypuk to convert the build system from

ant to gradle.  Removes linux and windows application launch scripts and
produces an executable jar with all resources included.

src/main/java/io/github/dsheirer/audio/AudioModule.java

@@ -0,0 +1,188 @@
+/*******************************************************************************
+ * sdrtrunk
+ * Copyright (C) 2014-2017 Dennis Sheirer
+ *
+ * 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 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/>
+ *
+ ******************************************************************************/
+package io.github.dsheirer.audio;
+
+import io.github.dsheirer.audio.squelch.ISquelchStateListener;
+import io.github.dsheirer.audio.squelch.SquelchState;
+import io.github.dsheirer.channel.metadata.Metadata;
+import io.github.dsheirer.dsp.filter.design.FilterDesignException;
+import io.github.dsheirer.dsp.filter.fir.FIRFilterSpecification;
+import io.github.dsheirer.dsp.filter.fir.remez.RemezFIRFilterDesigner;
+import io.github.dsheirer.dsp.filter.polyphase.PolyphaseFIRDecimatingFilter_RB;
+import io.github.dsheirer.module.Module;
+import io.github.dsheirer.sample.Listener;
+import io.github.dsheirer.sample.real.IFilteredRealBufferListener;
+import io.github.dsheirer.sample.real.RealBuffer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.ScheduledExecutorService;
+
+/**
+ * Provides packaging of demodulated audio sample buffers into audio packets for
+ * broadcast to registered audio packet listeners.  Includes audio packet
+ * metadata in constructed audio packets.
+ *
+ * Incorporates audio squelch state listener to control if audio packets are
+ * broadcast or ignored.
+ */
+public class AudioModule extends Module implements IAudioPacketProvider, IFilteredRealBufferListener,
+    ISquelchStateListener, Listener<RealBuffer>
+{
+    protected static final Logger mLog = LoggerFactory.getLogger(AudioModule.class);
+
+    private static float[] mDecimationCoefficients;
+
+    static
+    {
+        //Band-pass filter to both decimate (48kHz to 8kHz) and block 0 - 300 Hz (LTR signalling).
+        FIRFilterSpecification specification = FIRFilterSpecification.bandPassBuilder()
+            .sampleRate(48000)
+            .stopFrequency1(150)
+            .passFrequencyBegin(300)
+            .passFrequencyEnd(3500)
+            .stopFrequency2(4000)
+            .stopRipple(0.0004)
+            .passRipple(0.008)
+            .build();
+
+        RemezFIRFilterDesigner designer = new RemezFIRFilterDesigner(specification);
+
+        try
+        {
+            if(!designer.isValid())
+            {
+                throw new FilterDesignException("Couldn't design the audio decimation filter");
+            }
+
+            mDecimationCoefficients = designer.getImpulseResponse();
+        }
+        catch(FilterDesignException e)
+        {
+            mLog.debug("Error designing filter", e);
+        }
+    }
+
+    private SquelchStateListener mSquelchStateListener = new SquelchStateListener();
+    private SquelchState mSquelchState = SquelchState.SQUELCH;
+    private Listener<AudioPacket> mAudioPacketListener;
+    private PolyphaseFIRDecimatingFilter_RB mAudioDecimationFilter;
+    private Metadata mMetadata;
+
+    public AudioModule(Metadata metadata)
+    {
+        mMetadata = metadata;
+
+        mAudioDecimationFilter = new PolyphaseFIRDecimatingFilter_RB(mDecimationCoefficients, 6, 2.0f);
+        mAudioDecimationFilter.setListener(new Listener<RealBuffer>()
+        {
+            @Override
+            public void receive(RealBuffer realBuffer)
+            {
+                if(mAudioPacketListener != null)
+                {
+                    AudioPacket packet = new AudioPacket(realBuffer.getSamples(), mMetadata.copyOf());
+                    mAudioPacketListener.receive(packet);
+                }
+            }
+        });
+    }
+
+    @Override
+    public void dispose()
+    {
+        mSquelchStateListener = null;
+        mAudioPacketListener = null;
+    }
+
+    @Override
+    public void reset()
+    {
+    }
+
+    @Override
+    public void start(ScheduledExecutorService executor)
+    {
+        /* No start operations provided */
+    }
+
+    @Override
+    public void stop()
+    {
+        /* Issue an end audio packet in case a recorder is still rolling */
+        if(mAudioPacketListener != null)
+        {
+            mAudioPacketListener.receive(new AudioPacket(AudioPacket.Type.END, mMetadata.copyOf()));
+        }
+    }
+
+    /**
+     * Processes demodulated audio samples into audio packets with current audio
+     * metadata and sends to the registered listener
+     */
+    @Override
+    public void receive(RealBuffer buffer)
+    {
+        if(mAudioPacketListener != null && mSquelchState == SquelchState.UNSQUELCH)
+        {
+            mAudioDecimationFilter.receive(buffer);
+        }
+    }
+
+    @Override
+    public Listener<RealBuffer> getFilteredRealBufferListener()
+    {
+        return this;
+    }
+
+    @Override
+    public void setAudioPacketListener(Listener<AudioPacket> listener)
+    {
+        mAudioPacketListener = listener;
+    }
+
+    @Override
+    public void removeAudioPacketListener()
+    {
+        mAudioPacketListener = null;
+    }
+
+    @Override
+    public Listener<SquelchState> getSquelchStateListener()
+    {
+        return mSquelchStateListener;
+    }
+
+    /**
+     * Wrapper for squelch state listener
+     */
+    public class SquelchStateListener implements Listener<SquelchState>
+    {
+        @Override
+        public void receive(SquelchState state)
+        {
+            if(state == SquelchState.SQUELCH && mAudioPacketListener != null)
+            {
+                mAudioPacketListener.receive(new AudioPacket(AudioPacket.Type.END, mMetadata.copyOf()));
+            }
+
+            mSquelchState = state;
+        }
+    }
+}