Update UI thread with audio power

app/src/main/java/com/klangner/speechlab/MainActivity.java

@@ -1,27 +1,35 @@
 package com.klangner.speechlab;
 
-import android.media.AudioFormat;
 import android.media.AudioRecord;
-import android.media.MediaRecorder;
-import android.support.v7.app.ActionBarActivity;
 import android.os.Bundle;
+import android.os.Handler;
+import android.os.Looper;
+import android.os.Message;
+import android.support.v7.app.ActionBarActivity;
 import android.util.Log;
 import android.view.Menu;
 import android.view.MenuItem;
+import android.widget.TextView;
 
 
 public class MainActivity extends ActionBarActivity {
 
     private static final String TAG = "MainActivity";
+    private static final int MESSAGE_POWER = 1;
 
-    private AudioRecord recorder = null;
+    private Handler handler;
     private SignalPublisher signalPublisher = null;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
-        Log.v(TAG, "onCreate");
+        final TextView powerView = (TextView)findViewById(R.id.powerView);
+        handler = new Handler(Looper.getMainLooper()) {
+            public void handleMessage(Message msg) {
+                powerView.setText(msg.obj.toString());
+            }
+        };
     }
 
     @Override
@@ -56,7 +64,8 @@ private void startRecording() {
         signalPublisher = new SignalPublisher();
         signalPublisher.addPowerSubscriber(new SignalPublisher.PowerSubscriber() {
             public void onChanged(double power) {
-                Log.v(TAG, "Power: " + power);
+                Message msg = handler.obtainMessage(MESSAGE_POWER, power);
+                msg.sendToTarget();
             }
         });
         Thread thread = new Thread(signalPublisher);

app/src/main/java/com/klangner/speechlab/SignalPublisher.java

@@ -0,0 +1,88 @@
+package com.klangner.speechlab;
+
+import android.media.AudioFormat;
+import android.media.AudioRecord;
+import android.media.MediaRecorder;
+import android.util.Log;
+
+/**
+ * Signal processing publisher.
+ * Connects to audio and process incoming data.
+ * Allow subscribing to different audio features.
+ * This class works in it own thread. You can't update UI in callback from this class.
+ */
+public class SignalPublisher implements Runnable{
+
+    private static final String TAG = "SignalPublisher";
+    private static final int SAMPLE_SIZE = 2048;
+    private static final int RECORDER_SAMPLERATE = 44100;
+    private static final int RECORDER_CHANNELS = AudioFormat.CHANNEL_IN_MONO;
+    private static final int RECORDER_AUDIO_ENCODING = AudioFormat.ENCODING_PCM_16BIT;
+
+    public interface PowerSubscriber{
+        void onChanged(double power);
+    }
+
+    private final AudioRecord recorder;
+    private boolean isRunning = false;
+    private PowerSubscriber powerSubscriber = null;
+
+
+    public SignalPublisher(){
+        recorder = initAudioCapture();
+    }
+
+    @Override
+    public void run() {
+        short[] sample = new short[SAMPLE_SIZE];
+        android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND);
+        isRunning = true;
+        recorder.startRecording();
+        while (isRunning) {
+            recorder.read(sample, 0, SAMPLE_SIZE);
+            if(powerSubscriber != null){
+                double power = SignalPublisher.logPower(sample);
+                powerSubscriber.onChanged(power);
+            }
+        }
+        releaseAudioCapture();
+    }
+
+    public void stop(){
+        isRunning = false;
+    }
+
+    public void addPowerSubscriber(PowerSubscriber subscriber){
+        powerSubscriber = subscriber;
+    }
+
+    private AudioRecord initAudioCapture() {
+        Log.v(TAG, "Init audio");
+        int bufferSize = AudioRecord.getMinBufferSize(RECORDER_SAMPLERATE, RECORDER_CHANNELS, RECORDER_AUDIO_ENCODING);
+        return new AudioRecord(MediaRecorder.AudioSource.MIC, RECORDER_SAMPLERATE,
+                RECORDER_CHANNELS, RECORDER_AUDIO_ENCODING, bufferSize);
+    }
+
+    private void releaseAudioCapture() {
+        Log.v(TAG, "Destroy audio");
+        if(recorder != null) {
+            recorder.release();
+        }
+    }
+
+    /** Signal power for the whole sample */
+    private static double power(short[] data){
+        double sum = 0;
+        for(short x: data) {
+            sum += Math.pow(x, 2);
+        }
+        return sum/(2*(data.length+1));
+    }
+
+
+    /** Signal power int logarithmic scale. */
+    private static double logPower(short[] data){
+        return Math.log10(power(data));
+    }
+
+}