Androidで周波数解析

AndroidFFTSample.java

public class MainActivity extends Activity {

	// サンプリングレート
	int SAMPLING_RATE = 44100;
	// FFTのポイント数
	int FFT_SIZE = 4096;

	// デシベルベースラインの設定
	double dB_baseline = Math.pow(2, 15) * FFT_SIZE * Math.sqrt(2);

	// 分解能の計算
	double resol = ((SAMPLING_RATE / (double) FFT_SIZE));

	AudioRecord audioRec = null;
	boolean bIsRecording = false;
	int bufSize;
	Thread fft;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		bufSize = AudioRecord.getMinBufferSize(SAMPLING_RATE,
				AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);
	}

	
	@Override
	protected void onResume() {
		super.onResume();
		// AudioRecordの作成
		audioRec = new AudioRecord(MediaRecorder.AudioSource.MIC,
				SAMPLING_RATE, AudioFormat.CHANNEL_IN_MONO,
				AudioFormat.ENCODING_PCM_16BIT, bufSize * 2);
		audioRec.startRecording();
		bIsRecording = true;
		
		//フーリエ解析スレッド
		fft = new Thread(new Runnable() {
			@Override
			public void run() {
				byte buf[] = new byte[bufSize * 2];
				while (bIsRecording) {
					audioRec.read(buf, 0, buf.length);

					//エンディアン変換
					ByteBuffer bf = ByteBuffer.wrap(buf);
					bf.order(ByteOrder.LITTLE_ENDIAN);
					short[] s = new short[(int) bufSize];
					for (int i = bf.position(); i < bf.capacity() / 2; i++) {
						s[i] = bf.getShort();
					}

					//FFTクラスの作成と値の引き渡し
					FFT4g fft = new FFT4g(FFT_SIZE);
					double[] FFTdata = new double[FFT_SIZE];
					for (int i = 0; i < FFT_SIZE; i++) {
						FFTdata[i] = (double) s[i];
					}
					fft.rdft(1, FFTdata);

					// デシベルの計算
					double[] dbfs = new double[FFT_SIZE / 2];
					double max_db = -120d;
					int max_i = 0;
					for (int i = 0; i < FFT_SIZE; i += 2) {
						dbfs[i / 2] = (int) (20 * Math.log10(Math.sqrt(Math
								.pow(FFTdata[i], 2)
								+ Math.pow(FFTdata[i + 1], 2)) / dB_baseline));
						if (max_db < dbfs[i / 2]) {
							max_db = dbfs[i / 2];
							max_i = i / 2;
						}
					}
					
					//音量が最大の周波数と，その音量を表示
					Log.d("fft","周波数："+ resol * max_i+" [Hz] 音量：" +  max_db+" [dB]");
				}
				// 録音停止
				audioRec.stop();
				audioRec.release();
			}
		});
		//スレッドのスタート
		fft.start();
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}