Android AudioRecord giving many zero values

Using AudioRecord, I have attempted to write a test app to record a couple of seconds of audio to be displayed to the screen. However, I seem to get a repeating pattern of zero value regions as shown below. I'm not sure if this is normal behaviour or an error in my code.

MainActivity.java

public class MainActivity extends Activity implements OnClickListener 
{
    private static final int SAMPLE_RATE = 44100;
    private Button recordButton, playButton;
    private String filePath;
    private boolean recording;
    private AudioRecord record;
    private short[] data;
    private TestView testView;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button recordButton = (Button) this.findViewById(R.id.recordButton);
        recordButton.setOnClickListener(this);

        Button playButton = (Button)findViewById(R.id.playButton);
        playButton.setOnClickListener(this);

        FrameLayout frame = (FrameLayout)findViewById(R.id.myFrame);
        frame.addView(testView = new TestView(this));
    }

    @Override
    public void onClick(View v) 
    {
        if(v.getId() == R.id.recordButton)
        {
            if(!recording)
            {
                int bufferSize = AudioRecord.getMinBufferSize(  SAMPLE_RATE,
                                                                AudioFormat.CHANNEL_IN_MONO,
                                                                AudioFormat.ENCODING_PCM_16BIT);

                record = new AudioRecord(   MediaRecorder.AudioSource.MIC,
                                            SAMPLE_RATE,
                                            AudioFormat.CHANNEL_IN_MONO,
                                            AudioFormat.ENCODING_PCM_16BIT,
                                            bufferSize * 2);

                data = new short[10 * SAMPLE_RATE]; // Records up to 10 seconds

                new Thread()
                {
                    @Override
                    public void run() 
                    {
                        recordAudio();
                    }

                }.start();

                recording = true;

                Toast.makeText(this, "recording...", Toast.LENGTH_SHORT).show();
            }
            else
            {
                recording = false;
                Toast.makeText(this, "finished", Toast.LENGTH_SHORT).show();
            }
        }
        else if(v.getId() == R.id.playButton)
        {   
            testView.invalidate();
            Toast.makeText(this, "play/pause", Toast.LENGTH_SHORT).show();
        }
    }

    void recordAudio()
    {
        record.startRecording();
        int index = 0;
        while(recording)
        {
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            int result = record.read(data, index, SAMPLE_RATE); // read 1 second at a time
            if(result == AudioRecord.ERROR_INVALID_OPERATION || result == AudioRecord.ERROR_BAD_VALUE)
            {
                App.d("SOME SORT OF RECORDING ERROR MATE");
                return;
            }
            else
            {
                index += result; // increment by number of bytes read
                App.d("read: "+result);
            }
        }
        record.stop();
        data = Arrays.copyOf(data, index);

        testView.setData(data);
    }

    @Override
    protected void onPause() 
    {

        super.onPause();
    }
}

TestView.java

public class TestView extends View 
{
    private short[] data;
    Paint paint = new Paint();
    Path path = new Path();
    float min, max;

    public TestView(Context context) 
    {
        super(context);

        paint.setColor(Color.BLACK);
        paint.setStrokeWidth(1);
        paint.setStyle(Style.FILL_AND_STROKE);
    }

    void setData(short[] data)
    {
        min = Short.MAX_VALUE;
        max = Short.MIN_VALUE;
        this.data = data;
        for(int i = 0; i < data.length; i++)
        {
            if(data[i] < min)
                min = data[i];

            if(data[i] > max)
                max = data[i];
        }
    }

    @Override
    protected void onDraw(Canvas canvas)
    {
        canvas.drawRGB(255, 255, 255);
        if(data != null)
        {
            float interval = (float)this.getWidth()/data.length;
            for(int i = 0; i < data.length; i+=10)
                canvas.drawCircle(i*interval,(data[i]-min)/(max - min)*this.getHeight(),5 ,paint);

        }
        super.onDraw(canvas);
    }
}