Android audio is noisy about react-native-recording

[navrajkambo]

From matlab, I figured out that the data needs to be treated as datatype int16 instead of double, or float. The noise was caused by playing the data as datatype double. Audio is crystal clear with datatype int16! Incase anyone is wondering, below is my matlab test code and some modifications I made to your android module to test my theory...

playback.m matlab file for testing audi playback of recorded samples

Fs = 44100;
fid=fopen('record.pcm');
sig=double(fread(fid,inf,'int16')).'; % it's noisy
fclose(fid);

sig=int16(sig); % make it clean

player = audioplayer(sig,Fs);
player.play()

RecordingModule.java android java file for exporting pcm byte file to be played in audacity, and used in matlab

package cn.qiuxiang.react.recording;

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


import java.io.File; //added by Navraj Kambo
import java.io.FileInputStream; //added by Navraj Kambo
import java.io.FileNotFoundException; //added by Navraj Kambo
import java.io.FileOutputStream; //added by Navraj Kambo
import java.io.IOException; //added by Navraj Kambo
import android.os.Environment; //added by Navraj Kambo

import com.facebook.react.bridge.Arguments;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.bridge.ReactContextBaseJavaModule;
import com.facebook.react.bridge.ReactMethod;
import com.facebook.react.bridge.ReadableMap;
import com.facebook.react.bridge.WritableArray;
import com.facebook.react.modules.core.DeviceEventManagerModule;

class RecordingModule extends ReactContextBaseJavaModule {
    private static AudioRecord audioRecord;
    private final ReactApplicationContext reactContext;
    private DeviceEventManagerModule.RCTDeviceEventEmitter eventEmitter;
    private boolean running;
    private int bufferSize;
    private Thread recordingThread;

    RecordingModule(ReactApplicationContext reactContext) {
        super(reactContext);
        this.reactContext = reactContext;
    }

    @Override
    public String getName() {
        return "Recording";
    }

    @ReactMethod
    public void init(ReadableMap options) {
        if (eventEmitter == null) {
            eventEmitter = reactContext.getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class);
        }

        if (running || (recordingThread != null && recordingThread.isAlive())) {
            return;
        }

        if (audioRecord != null) {
            audioRecord.stop();
            audioRecord.release();
        }

        // for parameter description, see
        // https://developer.android.com/reference/android/media/AudioRecord.html

        int sampleRateInHz = 44100;
        if (options.hasKey("sampleRate")) {
            sampleRateInHz = options.getInt("sampleRate");
        }

        int channelConfig = AudioFormat.CHANNEL_IN_MONO;
        if (options.hasKey("channelsPerFrame")) {
            int channelsPerFrame = options.getInt("channelsPerFrame");

            // every other case --> CHANNEL_IN_MONO
            if (channelsPerFrame == 2) {
                channelConfig = AudioFormat.CHANNEL_IN_STEREO;
            }
        }

        // we support only 8-bit and 16-bit PCM
        int audioFormat = AudioFormat.ENCODING_PCM_16BIT;
        if (options.hasKey("bitsPerChannel")) {
            int bitsPerChannel = options.getInt("bitsPerChannel");

            if (bitsPerChannel == 8) {
                audioFormat = AudioFormat.ENCODING_PCM_8BIT;
            }
        }

        if (options.hasKey("bufferSize")) {
            this.bufferSize = options.getInt("bufferSize");
        } else {
            this.bufferSize = 8192;
        }

        audioRecord = new AudioRecord(
                MediaRecorder.AudioSource.MIC,
                sampleRateInHz,
                channelConfig,
                audioFormat,
                this.bufferSize * 2);

        recordingThread = new Thread(new Runnable() {
            public void run() {
                recording();
            }
        }, "RecordingThread");
    }

    @ReactMethod
    public void start() {
        if (!running && audioRecord != null && recordingThread != null) {
            running = true;
            audioRecord.startRecording();
            recordingThread.start();
        }
    }

    @ReactMethod
    public void stop() {
        if (audioRecord != null) {
            running = false;
            audioRecord.stop();
            audioRecord.release();
            audioRecord = null;
        }
    }
    private byte[] short2byte(short[] sData) { //added by Navraj Kambo
        int shortArrsize = sData.length; //added by Navraj Kambo
        byte[] bytes = new byte[shortArrsize * 2]; //added by Navraj Kambo
        for (int i = 0; i < shortArrsize; i++) { //added by Navraj Kambo
            bytes[i * 2] = (byte) (sData[i] & 0x00FF); //added by Navraj Kambo
            bytes[(i * 2) + 1] = (byte) (sData[i] >> 8); //added by Navraj Kambo
            sData[i] = 0; //added by Navraj Kambo
        } //added by Navraj Kambo
        return bytes; //added by Navraj Kambo
    } //added by Navraj Kambo
	
    private void recording() {
        short buffer[] = new short[bufferSize];
	String filepath = Environment.getExternalStorageDirectory().getPath(); //added by Navraj Kambo
        FileOutputStream os = null; //added by Navraj Kambo
        try { //added by Navraj Kambo
	    os = new FileOutputStream(filepath+"/download/record.pcm"); //added by Navraj Kambo
        } catch (FileNotFoundException e) { //added by Navraj Kambo
	    e.printStackTrace(); //added by Navraj Kambo
        } //added by Navraj Kambo
        while (running && !reactContext.getCatalystInstance().isDestroyed()) {
            WritableArray data = Arguments.createArray();
            audioRecord.read(buffer, 0, bufferSize);
            for (float value : buffer) {
                data.pushInt((int) value);
            }
            eventEmitter.emit("recording", data);
	    byte bdata[] = short2byte(buffer); //added by Navraj Kambo
	    try { //added by Navraj Kambo
                os.write(bdata, 0, bufferSize * 2); //added by Navraj Kambo
            } catch (IOException e) { //added by Navraj Kambo
                e.printStackTrace(); //added by Navraj Kambo
            } //added by Navraj Kambo
        }
	try { //added by Navraj Kambo
            os.close(); //added by Navraj Kambo
        } catch (IOException e) { //added by Navraj Kambo
            e.printStackTrace(); //added by Navraj Kambo
        } //added by Navraj Kambo
    }
}

Note: I also verified this with the streamed data from javascript/react-native

[qiuxiang]

raw data can't play directly before encoded to some audio format (wav, mp3 etc.)

[navrajkambo]

I played the file by importing the raw data into my Matlab workspace, and then used the sound(y,Fs) function in Matlab. I'll try an encode the data into a wav file using some third party software, and upload my results. Maybe the Matlab sound() requires something other than pcm 16 audio?

[qiuxiang]

I have not used matlab. But if you already encoded into wav file, you should be able to play it with an audio player.