Develop Reference

Mixing two16-bit encoded stereo PCM samples causing noise and distortion in the resulting audio

I get two different audio samples from two sources.
For microphone sound:
audioRecord =
new AudioRecord(MediaRecorder.AudioSource.DEFAULT, 44100, AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_PCM_16BIT,
(AudioRecord.getMinBufferSize(44100, AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_PCM_16BIT)*5));
For Internal sound:
audioRecord = new AudioRecord.Builder()
.setAudioPlaybackCaptureConfig(config)
.setAudioFormat(new AudioFormat.Builder()
.setEncoding(AudioFormat.ENCODING_PCM_16BIT)
.setSampleRate(44100)
.setChannelMask(AudioFormat.CHANNEL_IN_STEREO)
.build())
.setBufferSizeInBytes((AudioRecord.getMinBufferSize(44100, AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_PCM_16BIT)*5))
.build();
For reading from the audioRecord object we create individual frame objects(Custom objects called frame)-
private ByteBuffer pcmBuffer = ByteBuffer.allocateDirect(4096);
private Frame read() {
pcmBuffer.rewind();
int size = audioRecord.read(pcmBuffer, pcmBuffer.remaining());
if (size <= 0) {
return null;
}
return new Frame(pcmBuffer.array(),
pcmBuffer.arrayOffset(), size);
}
We create two separate LL(Linked List) for adding these frames that we get from read function.
private LinkedList internalAudioQueue = new LinkedList<>();
private LinkedList microphoneAudioQueue = new LinkedList<>();
public void onFrameReceived(Frame frame, boolean isInternalAudio) {
if (isInternalAudio) {
internalAudioQueue.add(frame);
} else {
microphoneAudioQueue.add(frame);
}
checkAndPoll();
}
Every time we add a frame in the respective LL we call the following checkAndPoll() function and depending upon the case pass the frame to the audioEncoder.
public void checkAndPoll() {
Frame frame1 = internalAudioQueue.poll();
Frame frame2 = microphoneAudioQueue.poll();
if (frame1 == null && frame2 != null) {
audioEncoder.inputPCMData(frame2);
} else if (frame1 != null && frame2 == null) {
audioEncoder.inputPCMData(frame1);
} else if (frame1 != null && frame2 != null) {
Frame frame = new Frame(PCMUtil.mix(frame1.getBuffer(), frame2.getBuffer(), frame1.getSize(), frame2.getSize(), false), frame1.getOrientation(), frame1.getSize());
audioEncoder.inputPCMData(frame);
}
}
Now we mix the audio samples in form of ByteBuffer from the two sources in this way taking Hendrik's help from this link.
public static byte[] mix(final byte[] a, final byte[] b, final boolean bigEndian) {
final byte[] aa;
final byte[] bb;
final int length = Math.max(a.length, b.length);
// ensure same lengths
if (a.length != b.length) {
aa = new byte[length];
bb = new byte[length];
System.arraycopy(a, 0, aa, 0, a.length);
System.arraycopy(b, 0, bb, 0, b.length);
} else {
aa = a;
bb = b;
}
// convert to samples
final int[] aSamples = toSamples(aa, bigEndian);
final int[] bSamples = toSamples(bb, bigEndian);
// mix by adding
final int[] mix = new int[aSamples.length];
for (int i=0; i<mix.length; i++) {
mix[i] = aSamples[i] + bSamples[i];
// enforce min and max (may introduce clipping)
mix[i] = Math.min(Short.MAX_VALUE, mix[i]);
mix[i] = Math.max(Short.MIN_VALUE, mix[i]);
}
// convert back to bytes
return toBytes(mix, bigEndian);
}
private static int[] toSamples(final byte[] byteSamples, final boolean bigEndian) {
final int bytesPerChannel = 2;
final int length = byteSamples.length / bytesPerChannel;
if ((length % 2) != 0) throw new IllegalArgumentException("For 16 bit audio, length must be even: " + length);
final int[] samples = new int[length];
for (int sampleNumber = 0; sampleNumber < length; sampleNumber++) {
final int sampleOffset = sampleNumber * bytesPerChannel;
final int sample = bigEndian
? byteToIntBigEndian(byteSamples, sampleOffset, bytesPerChannel)
: byteToIntLittleEndian(byteSamples, sampleOffset, bytesPerChannel);
samples[sampleNumber] = sample;
}
return samples;
}
private static byte[] toBytes(final int[] intSamples, final boolean bigEndian) {
final int bytesPerChannel = 2;
final int length = intSamples.length * bytesPerChannel;
final byte[] bytes = new byte[length];
for (int sampleNumber = 0; sampleNumber < intSamples.length; sampleNumber++) {
final byte[] b = bigEndian
? intToByteBigEndian(intSamples[sampleNumber], bytesPerChannel)
: intToByteLittleEndian(intSamples[sampleNumber], bytesPerChannel);
System.arraycopy(b, 0, bytes, sampleNumber * bytesPerChannel, bytesPerChannel);
}
return bytes;
}
// from https://github.com/hendriks73/jipes/blob/master/src/main/java/com/tagtraum/jipes/audio/AudioSignalSource.java#L238
private static int byteToIntLittleEndian(final byte[] buf, final int offset, final int bytesPerSample) {
int sample = 0;
for (int byteIndex = 0; byteIndex < bytesPerSample; byteIndex++) {
final int aByte = buf[offset + byteIndex] & 0xff;
sample += aByte << 8 * (byteIndex);
}
return (short)sample;
}
// from https://github.com/hendriks73/jipes/blob/master/src/main/java/com/tagtraum/jipes/audio/AudioSignalSource.java#L247
private static int byteToIntBigEndian(final byte[] buf, final int offset, final int bytesPerSample) {
int sample = 0;
for (int byteIndex = 0; byteIndex < bytesPerSample; byteIndex++) {
final int aByte = buf[offset + byteIndex] & 0xff;
sample += aByte << (8 * (bytesPerSample - byteIndex - 1));
}
return (short)sample;
}
private static byte[] intToByteLittleEndian(final int sample, final int bytesPerSample) {
byte[] buf = new byte[bytesPerSample];
for (int byteIndex = 0; byteIndex < bytesPerSample; byteIndex++) {
buf[byteIndex] = (byte)((sample >>> (8 * byteIndex)) & 0xFF);
}
return buf;
}
private static byte[] intToByteBigEndian(final int sample, final int bytesPerSample) {
byte[] buf = new byte[bytesPerSample];
for (int byteIndex = 0; byteIndex < bytesPerSample; byteIndex++) {
buf[byteIndex] = (byte)((sample >>> (8 * (bytesPerSample - byteIndex - 1))) & 0xFF);
}
return buf;
}
The mixed samples that I am getting have both distortion and noise. Not able to figure out what needs to be done to remove it. Any help here is appreciated.
Thanks in Advance!

I think if you're mixing, you should take the (weighted) average of both.
If you've got a sample 128 and 128, the result would be still 128, not 256, which could be out-of-range.
So just change your code to:
// mix by adding
final int[] mix = new int[aSamples.length];
for (int i=0; i<mix.length; i++) {
// calculating the average
mix[i] = (aSamples[i] + bSamples[i]) >> 1;
}
Does that work for you?

How to write a hash function in Android similar to the Python function?

I am currently developing a distributed system application. I want to verify a Python generated hash in the Android application. I have a python method to do hashing in given string variables.
This is the python function and it works well.
hash_value = hashlib.sha1("PARAMETER123".encode("UTF-8")).hexdigest()
I want to implement the same function in my Android application. I hope some expert can help as soon as possible.

You can try the following code snippet,
String text = "PARAMETER123";
MessageDigest md = MessageDigest.getInstance("SHA-1");
byte[] textBytes = text.getBytes("UTF-8");
md.update(textBytes, 0, textBytes.length);
byte[] sha1hash = md.digest();
String encrypted_text = = convertToHex(sha1hash);
and the convertToHex() method
private static String convertToHex(byte[] data) {
StringBuilder buf = new StringBuilder();
for (byte b : data) {
int halfbyte = (b >>> 4) & 0x0F;
int two_halfs = 0;
do {
buf.append((0 <= halfbyte) && (halfbyte <= 9) ? (char) ('0' + halfbyte) : (char) ('a' + (halfbyte - 10)));
halfbyte = b & 0x0F;
} while (two_halfs++ < 1);
}
return buf.toString();
}
This will convert a UTF-8 based text into a SHA1 hex.
Reference: https://stackoverflow.com/a/5980789/2506025

Here is a simple SHA1 method for Java:
String sha1Hash( String toHash )
{
String hash = null;
try
{
MessageDigest digest = MessageDigest.getInstance( "SHA-1" );
byte[] bytes = toHash.getBytes("UTF-8");
digest.update(bytes, 0, bytes.length);
bytes = digest.digest();
// This is ~55x faster than looping and String.formating()
hash = bytesToHex( bytes );
}
catch( NoSuchAlgorithmException e )
{
e.printStackTrace();
}
catch( UnsupportedEncodingException e )
{
e.printStackTrace();
}
return hash;
}
// http://stackoverflow.com/questions/9655181/convert-from-byte-array-to-hex-string-in-java
final protected static char[] hexArray = "0123456789ABCDEF".toCharArray();
public static String bytesToHex( byte[] bytes )
{
char[] hexChars = new char[ bytes.length * 2 ];
for( int j = 0; j < bytes.length; j++ )
{
int v = bytes[ j ] & 0xFF;
hexChars[ j * 2 ] = hexArray[ v >>> 4 ];
hexChars[ j * 2 + 1 ] = hexArray[ v & 0x0F ];
}
return new String( hexChars );
}
You can include those methods and call sha1hash.

How to aproach this in android? signed byte

I have a piece of problem that I want to achieve in android.
The formula is
Server Seed + Client Seed (->byte[4]) + Bet Number (->byte[4])
Double SHA2-512 hash the result
Keep taking groups of 3 bytes and converting to an integer, until a value less than 16 million is found. If you run out of bytes, hash it
again and start over.
Find the value's modulus of 1 million
The modulus is the bet result!
Which have an example code in C#
static bool VerifyBetResult(string serverSeed, int clientSeed, int betNumber,
long betResult, string serverSeedHash = null)
{
Func<string, byte[]> strtobytes = s => Enumerable
.Range(0, s.Length / 2)
.Select(x => byte.Parse(s.Substring(x * 2, 2), NumberStyles.HexNumber))
.ToArray();
byte[] server = strtobytes(serverSeed);
byte[] client = BitConverter.GetBytes(clientSeed).Reverse().ToArray();
byte[] num = BitConverter.GetBytes(betNumber).Reverse().ToArray();
byte[] serverhash = serverSeedHash == null ? null : strtobytes(serverSeedHash);
byte[] data = server.Concat(client).Concat(num).ToArray();
using (SHA512 sha512 = new SHA512Managed())
{
if (serverhash != null)
using (SHA256 sha256 = new SHA256Managed())
if (!sha256.ComputeHash(server).SequenceEqual(serverhash))
throw new Exception("Server seed hash does not match server seed");
byte[] hash = sha512.ComputeHash(sha512.ComputeHash(data));
while (true)
{
for (int x = 0; x <= 61; x += 3)
{
long result = (hash[x] << 16) | (hash[x + 1] << 8) | hash[x + 2];
if (result < 16000000)
return result % 1000000 == betResult;
}
hash = sha512.ComputeHash(hash);
}
}
}
Using these values
serverSeed = e600f76aa6c520dff7db34559bd05cb1048b1830a07cd81844147a19048fc9be;
clientSeed = 443944;
betNumber = 0;
serverHash = ca90022ac66a6a77d8b5072e101bff505c2bff552b1b9a0785f0c438d5b6228f;
I want to find the (result % 1000000) which should be = 563383
But I got -25564 and the serverHash does not match the serverSeed when hashing the seed to sha256
Update
This is my code:
private byte[] reverse(byte[] b){
int i = b.length - 1;
byte newB[] = new byte[4];
for(int x = 0; x < b.length; x++){
newB[x] = b[i];
i--;
}
return newB;
}
private byte[] strToByte(String s) {
int len = s.length();
byte[] data = new byte[len/2];
for(int i = 0; i < len; i+=2){
data[i/2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16));
}
return data;
}
private long verifyBet(){
//MessageDigest md256 = null;
MessageDigest md512 = null;
try {
//md256 = MessageDigest.getInstance("SHA-256");
md512 = MessageDigest.getInstance("SHA-512");
} catch (Exception e) {
e.printStackTrace();
}
String //res = "ServerSeed = ",
sSeed = "e600f76aa6c520dff7db34559bd05cb1048b1830a07cd81844147a19048fc9be";
//sHash = "ca90022ac66a6a77d8b5072e101bff505c2bff552b1b9a0785f0c438d5b6228f";
int cSeed = 443944,
num = 0;
byte serverSeed[] = strToByte(sSeed),
//serverHash[] = strToByte(sHash),
clientSeed[] = reverse(ByteBuffer.allocate(4).putInt(cSeed).array()),
betNumber[] = reverse(ByteBuffer.allocate(4).putInt(num).array());
byte data[] = ByteBuffer.allocate(serverSeed.length + clientSeed.length + betNumber.length)
.put(serverSeed).put(clientSeed).put(betNumber).array();
data = md512.digest(data);
data = md512.digest(data);
long secret = 0;
boolean found = false;
while(!found){
for(int x = 0; x <= 61; x += 3){
long result = (data[x] << 16 | data[x+1] << 8) | data[x+2];
if (result < 16000000){
secret = result % 1000000;
found = true;
}
}
data = md512.digest(data);
}
return secret;
}
After much more research I found that byte in java is signed while the code I am basing from is calculating in unsigned byte which is why I am getting result in negative..
How can I get set of bytes in 'unsigned' form?

After so much research and testing. I finally got it. This is the code.
private byte[] strToByte(String s) {
int len = s.length();
byte[] data = new byte[len/2];
for(int i = 0; i < len; i+=2){
data[i/2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16));
}
return data;
}
private long verifyBet(int _num){
MessageDigest md512 = null;
try {
md512 = MessageDigest.getInstance("SHA-512");
} catch (Exception e) {
e.printStackTrace();
}
String sSeed = "e600f76aa6c520dff7db34559bd05cb1048b1830a07cd81844147a19048fc9be";
int cSeed = 443944,
num = _num;
byte serverSeed[] = strToByte(sSeed),
clientSeed[] = ByteBuffer.allocate(4).putInt(cSeed).array(),
betNumber[] = ByteBuffer.allocate(4).putInt(num).array();
byte data[] = ByteBuffer.allocate(serverSeed.length + clientSeed.length + betNumber.length)
.put(serverSeed).put(clientSeed).put(betNumber).array();
data = md512.digest(data);
data = md512.digest(data);
long secret = 0;
boolean found = false;
while(!found){
for(int x = 0; x <= 61; x += 3){
long result = ((data[x] & 0xFF) << 16 | (data[x+1] & 0xFF) << 8) | data[x+2] & 0xFF;
if (result < 16000000){
secret = result % 1000000;
found = true;
x = 62;
}
}
data = md512.digest(data);
}
return secret;
}

How to restore base64 encoded opencv java matrix to C++ cv::Mat?

I'm extracting ORB descriptors of an image in android using opencv which is then sent to a C++ server using a socket. To send it via the socket I'm encoding the opencv mat of descriptors to base64 using the below java code.
public static String matToJson(Mat mat){
JsonObject obj = new JsonObject();
if(mat.isContinuous()){
int cols = mat.cols();
int rows = mat.rows();
int elemSize = (int) mat.elemSize();
byte[] data = new byte[cols * rows * elemSize];
mat.get(0, 0, data);
obj.addProperty("rows", mat.rows());
obj.addProperty("cols", mat.cols());
obj.addProperty("type", mat.type());
// We cannot set binary data to a json object, so:
// Encoding data byte array to Base64.
String dataString = new String(Base64.encode(data, Base64.DEFAULT));
obj.addProperty("data", dataString);
Gson gson = new Gson();
String json = gson.toJson(obj);
return json;
} else {
Log.e(TAG, "Mat not continuous.");
}
public static Mat matFromJson(String json){
JsonParser parser = new JsonParser();
JsonObject JsonObject = parser.parse(json).getAsJsonObject();
int rows = JsonObject.get("rows").getAsInt();
int cols = JsonObject.get("cols").getAsInt();
int type = JsonObject.get("type").getAsInt();
String dataString = JsonObject.get("data").getAsString();
byte[] data = Base64.decode(dataString.getBytes(), Base64.DEFAULT);
Mat mat = new Mat(rows, cols, type);
mat.put(0, 0, data);
return mat;
}
The output from matToJson() looks like below:
{"rows":26,"cols":32,"type":0,"data":"aSbt5TQabzJ9qv7s3ymQchrEfSyp8OWO5v8nkG6oUiFAMLFkAExBEGCgJggSF0AyAFRoCAlgsADJ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\nwij1oBl6rKxJm/IRoVi300g4gYpsHDtr2jPZqzR42MDCIA\u003d\u003d\n"}
the encoded base64 string in the "data" key is the Matrix data.
The above json string is sent to the server via socket.
Now, I need to convert the "data" value of the json string back to cv::Mat in C++, so how do i get back the matrix from the above base64 string ?

Assuming that you read the data from the JSON, you can create the Mat like this:
int rows = 26;
int cols = 32;
int type = 0;
string data = "aSbt5TQabz...";
string decoded_data = base64_decode(data);
Mat m(rows, cols, type, (void*)decoded_data.data());
Code for base64_decode is from here
NOTE
I needed to manually convert the characted \u003D to = to make it work. You can avoid to escape HTML characters using Gson gson = new GsonBuilder().disableHtmlEscaping().create();. See here.
Code:
#include <opencv2\opencv.hpp>
#include <vector>
#include <string>
using namespace std;
using namespace cv;
// Code from: http://www.adp-gmbh.ch/cpp/common/base64.html
static const std::string base64_chars =
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/";
static inline bool is_base64(unsigned char c) {
return (isalnum(c) || (c == '+') || (c == '/'));
}
std::string base64_decode(std::string const& encoded_string) {
int in_len = encoded_string.size();
int i = 0;
int j = 0;
int in_ = 0;
unsigned char char_array_4[4], char_array_3[3];
std::string ret;
while (in_len-- && (encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
char_array_4[i++] = encoded_string[in_]; in_++;
if (i == 4) {
for (i = 0; i < 4; i++)
char_array_4[i] = base64_chars.find(char_array_4[i]);
char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
for (i = 0; (i < 3); i++)
ret += char_array_3[i];
i = 0;
}
}
if (i) {
for (j = i; j < 4; j++)
char_array_4[j] = 0;
for (j = 0; j < 4; j++)
char_array_4[j] = base64_chars.find(char_array_4[j]);
char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];
for (j = 0; (j < i - 1); j++) ret += char_array_3[j];
}
return ret;
}
int main()
{
// Read your JSON here...
int rows = 26;
int cols = 32;
int type = 0;
//string data(L"aSbt5TQabzJ9qv7s3ymQchrEfSyp8OWO5v8nkG6oUiFAMLFkAExBEGCgJggSF0AyAFRoCAlgsADJ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\nwij1oBl6rKxJm/IRoVi300g4gYpsHDtr2jPZqzR42MDCIA\u003d\u003d\n");
string data = "aSbt5TQabzJ9qv7s3ymQchrEfSyp8OWO5v8nkG6oUiFAMLFkAExBEGCgJggSF0AyAFRoCAlgsADJ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\nwij1oBl6rKxJm/IRoVi300g4gYpsHDtr2jPZqzR42MDCIA==\n";
string decoded_data = base64_decode(data);
Mat m(rows, cols, type, (void*)decoded_data.data());
cout << m << endl;
return 0;
}

How to covert String to byte for BLE mBluetoothGatt.writeCharacteristic?

I am developing in Android BLE.
I try to send string to BLE device(like TI CC2541) , and it seems can not send string direct to BLE device.
It need to convert the String to Byte.
I have search some information , there has someone use URLEncoder.encode.
But I am not sure which is the answer what I need.
But how to convert the String to Byte?
The following code is writeCharacteristic for BLE
public void writeString(String text) {
// TODO Auto-generated method stub
BluetoothGattService HelloService = mBluetoothGatt.getService(HELLO_SERVICE_UUID);
BluetoothGattCharacteristic StringCharacteristic = HelloService.getCharacteristic(UUID_HELLO_CHARACTERISTIC_WRITE_STRING);
mBluetoothGatt.setCharacteristicNotification(StringCharacteristic , true);
int A = Integer.parseInt(text);
//How to convert the String to Byte here and set the Byte to setValue ?????
StringCharacteristic .setValue(A, BluetoothGattCharacteristic.FORMAT_UINT8, 0);
mBluetoothGatt.writeCharacteristic(StringCharacteristic );
Log.d(TAG, "StepCount Characteristic End!");
}
How to convert the String to Byte?

Where you get your String:
byte[] strBytes = text.getBytes();
byte[] bytes = context.yourmWriteCharacteristic.getValue();
Please add a null check too like:
if (bytes == null) {
Log.w("Cannot get Values from mWriteCharacteristic.");
dismiss();// equivalent action
}
if (bytes.length <= strBytes.length) {
for(int i = 0; i < bytes.length; i++) {
bytes[i] = strBytes[i];
}
} else {
for (int i = 0; i < strBytes.length; i++) {
bytes[i] = strBytes[i];
}
}
Now, something like:
StepCount_Characteristic.setValue(bytes);
mBluetoothGatt.writeCharacteristic(StepCount_Characteristic);

I found the following code help me convert the string.
private byte[] parseHex(String hexString) {
hexString = hexString.replaceAll("\\s", "").toUpperCase();
String filtered = new String();
for(int i = 0; i != hexString.length(); ++i) {
if (hexVal(hexString.charAt(i)) != -1)
filtered += hexString.charAt(i);
}
if (filtered.length() % 2 != 0) {
char last = filtered.charAt(filtered.length() - 1);
filtered = filtered.substring(0, filtered.length() - 1) + '0' + last;
}
return hexStringToByteArray(filtered);
}
public static byte[] hexStringToByteArray(String s) {
int len = s.length();
byte[] data = new byte[len / 2];
for (int i = 0; i < len; i += 2) {
data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
+ Character.digit(s.charAt(i+1), 16));
}
return data;
}
private int hexVal(char ch) {
return Character.digit(ch, 16);
}
If you want to convert string value. you just need to call like the following:
String text;
byte[] value = parseHex(text);