Audio amplitude detector for Android.

AudioMeter.java

import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder.AudioSource;
import android.os.Process;

public class AudioMeter extends Thread {
	/////////////////////////////////////////////////////////////////
	// PUBLIC CONSTANTS

	// Convenience constants
	public static final int AMP_SILENCE = 0;
	public static final int AMP_NORMAL_BREATHING = 10;
	public static final int AMP_MOSQUITO = 20;
	public static final int AMP_WHISPER = 30;
	public static final int AMP_STREAM = 40;
	public static final int AMP_QUIET_OFFICE = 50;
	public static final int AMP_NORMAL_CONVERSATION = 60;
	public static final int AMP_HAIR_DRYER = 70;
	public static final int AMP_GARBAGE_DISPOSAL = 80;

	/////////////////////////////////////////////////////////////////
	// PRIVATE CONSTANTS

	private static final float MAX_REPORTABLE_AMP = 32767f;
	private static final float MAX_REPORTABLE_DB = 90.3087f;

	/////////////////////////////////////////////////////////////////
	// PRIVATE MEMBERS

	private AudioRecord mAudioRecord;
	private int mSampleRate;
	private short mAudioFormat;
	private short mChannelConfig;

	private short[] mBuffer;
	private int mBufferSize = AudioRecord.ERROR_BAD_VALUE;

	private int mLocks = 0;

	/////////////////////////////////////////////////////////////////
	// CONSTRUCTOR

	private AudioMeter() {
		Process.setThreadPriority(Process.THREAD_PRIORITY_URGENT_AUDIO);
		createAudioRecord();
	}

	/////////////////////////////////////////////////////////////////
	// PUBLIC METHODS

	public static AudioMeter getInstance() {
		return InstanceHolder.INSTANCE;
	}

	public float getAmplitude() {
		return (float) (MAX_REPORTABLE_DB + (20 * Math.log10(getRawAmplitude() / MAX_REPORTABLE_AMP)));
	}

	public synchronized void startRecording() {
		if (mAudioRecord == null || mAudioRecord.getState() != AudioRecord.STATE_INITIALIZED) {
			throw new IllegalStateException("startRecording() called on an uninitialized AudioRecord.");
		}

		if (mLocks == 0) {
			mAudioRecord.startRecording();
		}

		mLocks++;
	}

	public synchronized void stopRecording() {
		mLocks--;

		if (mLocks == 0) {
			if (mAudioRecord != null) {
				mAudioRecord.stop();
				mAudioRecord.release();
				mAudioRecord = null;
			}
		}
	}

	/////////////////////////////////////////////////////////////////
	// PRIVATE METHODS

	private void createAudioRecord() {
		if (mSampleRate > 0 && mAudioFormat > 0 && mChannelConfig > 0) {
			mAudioRecord = new AudioRecord(AudioSource.MIC, mSampleRate, mChannelConfig, mAudioFormat, mBufferSize);

			return;
		}

		// Find best/compatible AudioRecord
		for (int sampleRate : new int[] { 8000, 11025, 16000, 22050, 32000, 44100, 47250, 48000 }) {
			for (short audioFormat : new short[] { AudioFormat.ENCODING_PCM_16BIT, AudioFormat.ENCODING_PCM_8BIT }) {
				for (short channelConfig : new short[] { AudioFormat.CHANNEL_IN_MONO, AudioFormat.CHANNEL_IN_STEREO,
					AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.CHANNEL_CONFIGURATION_STEREO }) {

					// Try to initialize
					try {
						mBufferSize = AudioRecord.getMinBufferSize(sampleRate, channelConfig, audioFormat);

						if (mBufferSize < 0) {
							continue;
						}

						mBuffer = new short[mBufferSize];
						mAudioRecord = new AudioRecord(AudioSource.MIC, sampleRate, channelConfig, audioFormat,
								mBufferSize);

						if (mAudioRecord.getState() == AudioRecord.STATE_INITIALIZED) {
							mSampleRate = sampleRate;
							mAudioFormat = audioFormat;
							mChannelConfig = channelConfig;

							return;
						}

						mAudioRecord.release();
						mAudioRecord = null;
					}
					catch (Exception e) {
						// Do nothing
					}
				}
			}
		}
	}

	private int getRawAmplitude() {
		if (mAudioRecord == null) {
			createAudioRecord();
		}

		final int bufferReadSize = mAudioRecord.read(mBuffer, 0, mBufferSize);

		if (bufferReadSize < 0) {
			return 0;
		}

		int sum = 0;
		for (int i = 0; i < bufferReadSize; i++) {
			sum += Math.abs(mBuffer[i]);
		}

		if (bufferReadSize > 0) {
			return sum / bufferReadSize;
		}

		return 0;
	}

	/////////////////////////////////////////////////////////////////
	// PRIVATE CLASSES

	private static class InstanceHolder {
		private static final AudioMeter INSTANCE = new AudioMeter();
	}
}