Android Audio Processing: Fundamentals and Best Practices

In the previous chapter, we explored image processing—such as loading, editing, and saving images—in depth. Next, we turn our attention to audio processing: learning how to play, record, and process audio within Android applications. Audio processing is essential across many application domains—especially in music players, voice recording apps, and games.

1. Audio Playback

In Android, audio playback is commonly handled using the MediaPlayer class, which provides a rich set of APIs for managing audio playback. Below is a basic example of audio playback.

Example: Simple Audio Playback

Assume we want to play an audio file named sound.mp3, stored in the res/raw directory.

import android.media.MediaPlayer;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

public class AudioActivity extends AppCompatActivity {
    private MediaPlayer mediaPlayer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_audio);
        
        // Initialize MediaPlayer
        mediaPlayer = MediaPlayer.create(this, R.raw.sound);
    }

    @Override
    protected void onDestroy() {
        // Release resources
        if (mediaPlayer != null) {
            mediaPlayer.release();
            mediaPlayer = null;
        }
        super.onDestroy();
    }

    // Play audio
    public void playAudio() {
        if (mediaPlayer != null) {
            mediaPlayer.start();
        }
    }
    
    // Pause audio
    public void pauseAudio() {
        if (mediaPlayer != null && mediaPlayer.isPlaying()) {
            mediaPlayer.pause();
        }
    }
    
    // Stop audio
    public void stopAudio() {
        if (mediaPlayer != null) {
            mediaPlayer.stop();
            mediaPlayer.prepareAsync(); // Prepare for next playback
        }
    }
}

In this example, we create a MediaPlayer instance using MediaPlayer.create(). We then control playback using methods such as start(), pause(), and stop().

2. Audio Recording

Beyond playback, audio recording is another common requirement. Android provides the AudioRecord class for low-level audio capture. Below is a simple audio recording example.

Example: Simple Audio Recording

import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.os.Environment;
import androidx.appcompat.app.AppCompatActivity;
import java.io.FileOutputStream;
import java.io.IOException;

public class RecordActivity extends AppCompatActivity {
    private static final int RECORDER_AUDIO_SOURCE = MediaRecorder.AudioSource.MIC;
    private static final int RECORDER_OUTPUT_FORMAT = AudioFormat.ENCODING_PCM_16BIT;
    private static final int RECORDER_CHANNELS = AudioFormat.CHANNEL_IN_MONO;
    private static final int RECORDER_SAMPLERATE = 44100;
    private static final String FILE_PATH = Environment.getExternalStorageDirectory().getPath() + "/recorded_audio.pcm";
    
    private AudioRecord audioRecord;
    private boolean isRecording = false;

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

    public void startRecording() {
        audioRecord = new AudioRecord(RECORDER_AUDIO_SOURCE, RECORDER_SAMPLERATE,
                RECORDER_CHANNELS, RECORDER_OUTPUT_FORMAT, AudioRecord.getMinBufferSize(RECORDER_SAMPLERATE, RECORDER_CHANNELS, RECORDER_OUTPUT_FORMAT));

        audioRecord.startRecording();
        isRecording = true;

        new Thread(new Runnable() {
            @Override
            public void run() {
                writeAudioData();
            }
        }).start();
    }

    private void writeAudioData() {
        byte[] data = new byte[1024];
        try (FileOutputStream os = new FileOutputStream(FILE_PATH)) {
            while (isRecording) {
                int read = audioRecord.read(data, 0, data.length);
                if (read > 0) {
                    os.write(data, 0, read);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void stopRecording() {
        if (audioRecord != null) {
            isRecording = false;
            audioRecord.stop();
            audioRecord.release();
            audioRecord = null;
        }
    }
}

In this example, AudioRecord captures raw audio data. The recording runs on a separate thread to avoid blocking the main UI thread. The captured audio is saved in PCM format to the specified file path.

3. Audio Effects Processing

For applying real-time audio effects, Android offers built-in classes such as AudioEffect. Common effects include reverb, equalization, and more. Below is a simple example demonstrating how to apply an equalizer effect.

Example: Adding an Equalizer Effect

import android.media.audiofx.Equalizer;
import android.media.MediaPlayer;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

public class EqualizerActivity extends AppCompatActivity {
    private MediaPlayer mediaPlayer;
    private Equalizer equalizer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_equalizer);
        
        mediaPlayer = MediaPlayer.create(this, R.raw.sound);
        equalizer = new Equalizer(0, mediaPlayer.getAudioSessionId());
        equalizer.setEnabled(true);

        // Configure equalizer bands
        for (short i = 0; i < equalizer.getNumberOfBands(); i++) {
            equalizer.setBandLevel(i, (short) (equalizer.getBandLevelRange()[1] / 2));
        }
    }

    @Override
    protected void onDestroy() {
        if (equalizer != null) {
            equalizer.release();
        }
        if (mediaPlayer != null) {
            mediaPlayer.release();
        }
        super.onDestroy();
    }
}

Here, we instantiate an Equalizer tied to the MediaPlayer’s audio session and enable it. Then, we set each frequency band to its mid-range gain level—enhancing tonal balance and overall listening experience, especially useful in music applications.

4. Summary

In this chapter, we covered three core aspects of audio handling in Android:

• Playing audio using MediaPlayer,
• Recording raw audio with AudioRecord,
• Enhancing audio quality using built-in effects like Equalizer.

These foundational capabilities empower developers to build rich, interactive audio experiences—particularly valuable in media-centric applications.

In the next chapter, we’ll discuss app signing—a critical step before publishing your application. As we progressively build and refine our app, mastering proper signing procedures will ensure secure distribution and compliance with Google Play requirements.