How to detect if there is a sound in android?

Question

I am new to android development. Ive to make an application which detects sound and plays music. I have already taken care of music playing part but the problem is that I don't understand how to put a condition to check that whether there is even a sound or not Im using eclipse and android API 20 and voice recognition intent. Kindly look at the following code.

import android.app.Activity;
import android.os.Bundle;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.speech.RecognizerIntent;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.List;

/**
 * A very simple application to handle Voice Recognition intents
 * and display the results
 */
public class MainActivity extends Activity
{

    private static final int REQUEST_CODE = 1234;
    private ListView wordsList;

    /**
     * Called with the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.voice_recog);

        Button speakButton = (Button) findViewById(R.id.speakButton);

        wordsList = (ListView) findViewById(R.id.list);

        // Disable button if no recognition service is present
        PackageManager pm = getPackageManager();
        List<ResolveInfo> activities = pm.queryIntentActivities(
                new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH), 0);
        if (activities.size() == 0)
        {
            speakButton.setEnabled(false);
            speakButton.setText("Recognizer not present");
        }
        else
        {startVoiceRecognitionActivity();}
    }

    /**
     * Handle the action of the button being clicked
     */




    /**
     * Fire an intent to start the voice recognition activity.
     */
    private void startVoiceRecognitionActivity()
    {
        Intent intent = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
        intent.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL,
                RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
        intent.putExtra(RecognizerIntent.EXTRA_PROMPT, "Voice recognition Demo...");
        startActivityForResult(intent, REQUEST_CODE);
    }

    /**
     * Handle the results from the voice recognition activity.
     */
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data)
    {
        if (requestCode == REQUEST_CODE && resultCode == RESULT_OK)
        {
            // Populate the wordsList with the String values the recognition engine thought it heard
            ArrayList<String> matches = data.getStringArrayListExtra(
                    RecognizerIntent.EXTRA_RESULTS);
            wordsList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,
                    matches));
        }
        super.onActivityResult(requestCode, resultCode, data);
    }
}