要实现安卓音频回环，可以使用Android的AudioTrack和AudioRecord类来捕获和播放音频数据。下面是一个简单的示例代码：

import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioRecord;
import android.media.AudioTrack;
import android.media.MediaRecorder;

public class AudioLoopback {

    private static final int SAMPLE_RATE = 44100;
    private static final int CHANNEL_CONFIG = AudioFormat.CHANNEL_IN_MONO;
    private static final int AUDIO_FORMAT = AudioFormat.ENCODING_PCM_16BIT;

    private AudioRecord audioRecord;
    private AudioTrack audioTrack;
    private boolean isLoopbackRunning;

    public void startLoopback() {
        int bufferSize = AudioRecord.getMinBufferSize(SAMPLE_RATE, CHANNEL_CONFIG, AUDIO_FORMAT);
        audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, SAMPLE_RATE, CHANNEL_CONFIG, AUDIO_FORMAT, bufferSize);
        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, SAMPLE_RATE, AudioFormat.CHANNEL_OUT_MONO, AUDIO_FORMAT, bufferSize, AudioTrack.MODE_STREAM);

        isLoopbackRunning = true;
        audioRecord.startRecording();
        audioTrack.play();

        new Thread(new Runnable() {
            @Override
            public void run() {
                byte[] buffer = new byte[bufferSize];
                while (isLoopbackRunning) {
                    // 从音频录制设备读取数据
                    audioRecord.read(buffer, 0, bufferSize);
                    // 将数据写入音频播放设备
                    audioTrack.write(buffer, 0, bufferSize);
                }
            }
        }).start();
    }

    public void stopLoopback() {
        isLoopbackRunning = false;
        audioRecord.stop();
        audioTrack.stop();
        audioRecord.release();
        audioTrack.release();
    }
}

使用上述代码，可以通过调用startLoopback()方法来开始音频回环，通过调用stopLoopback()方法来停止音频回环。请注意，在使用这些代码之前，需要在AndroidManifest.xml文件中添加相应的权限，如下所示：

此外，还需要确保在运行时动态请求录音权限。