The algorithm works fine here
https://sites.google.com/site/mikescoderama/pitch-shifting
My mistake was how I read the wave header and wave data. I post here the full working code
WARNING: this code only works for 16-bit (stereo / mono) PCM waves. It can be easily adapted to work with 8-bit PCM.
static void Main(string[] args) { // Read header, data and channels as separated data // Normalized data stores. Store values in the format -1.0 to 1.0 byte[] waveheader = null; byte[] wavedata = null; int sampleRate = 0; float[] in_data_l = null; float[] in_data_r = null; GetWaveData("sound.wav", out waveheader, out wavedata, out sampleRate, out in_data_l, out in_data_r); // // Apply Pitch Shifting // if(in_data_l != null) PitchShifter.PitchShift(2f, in_data_l.Length, (long)1024, (long)10, sampleRate, in_data_l); if(in_data_r != null) PitchShifter.PitchShift(2f, in_data_r.Length, (long)1024, (long)10, sampleRate, in_data_r); // // Time to save the processed data // // Backup wave data byte[] copydata = new byte[wavedata.Length]; Array.Copy(wavedata, copydata, wavedata.Length); GetWaveData(in_data_l, in_data_r, ref wavedata); // // Check if data actually changed // bool noChanges = true; for (int i = 0; i < wavedata.Length; i++) { if (wavedata[i] != copydata[i]) { noChanges = false; Console.WriteLine("Data has changed!"); break; } } if(noChanges) Console.WriteLine("Data has no changes"); // Save modified wavedata string targetFilePath = "sound_low.wav"; if (File.Exists(targetFilePath)) File.Delete(targetFilePath); using (BinaryWriter writer = new BinaryWriter(File.OpenWrite(targetFilePath))) { writer.Write(waveheader); writer.Write(wavedata); } Console.ReadLine(); } // Returns left and right float arrays. 'right' will be null if sound is mono. public static void GetWaveData(string filename, out byte[] header, out byte[] data, out int sampleRate, out float[] left, out float[] right) { byte[] wav = File.ReadAllBytes(filename); // Determine if mono or stereo int channels = wav[22]; // Forget byte 23 as 99.999% of WAVs are 1 or 2 channels // Get sample rate sampleRate = BitConverter.ToInt32(wav, 24); int pos = 12; // Keep iterating until we find the data chunk (ie 64 61 74 61 ...... (ie 100 97 116 97 in decimal)) while(!(wav[pos]==100 && wav[pos+1]==97 && wav[pos+2]==116 && wav[pos+3]==97)) { pos += 4; int chunkSize = wav[pos] + wav[pos + 1] * 256 + wav[pos + 2] * 65536 + wav[pos + 3] * 16777216; pos += 4 + chunkSize; } pos += 4; int subchunk2Size = BitConverter.ToInt32(wav, pos); pos += 4; // Pos is now positioned to start of actual sound data. int samples = subchunk2Size / 2; // 2 bytes per sample (16 bit sound mono) if (channels == 2) samples /= 2; // 4 bytes per sample (16 bit stereo) // Allocate memory (right will be null if only mono sound) left = new float[samples]; if (channels == 2) right = new float[samples]; else right = null; header = new byte[pos]; Array.Copy(wav, header, pos); data = new byte[subchunk2Size]; Array.Copy(wav, pos, data, 0, subchunk2Size); // Write to float array/s: int i=0; while (pos < subchunk2Size) { left[i] = BytesToNormalized_16(wav[pos], wav[pos + 1]); pos += 2; if (channels == 2) { right[i] = BytesToNormalized_16(wav[pos], wav[pos + 1]); pos += 2; } i++; } } // Return byte data from left and right float data. Ignore right when sound is mono public static void GetWaveData(float[] left, float[] right, ref byte[] data) { // Calculate k // This value will be used to convert float to Int16 // We are not using Int16.Max to avoid peaks due to overflow conversions float k = (float)Int16.MaxValue / left.Select(x => Math.Abs(x)).Max(); // Revert data to byte format Array.Clear(data, 0, data.Length); int dataLenght = left.Length; int byteId = -1; using (BinaryWriter writer = new BinaryWriter(new MemoryStream(data))) { for (int i = 0; i < dataLenght; i++) { byte byte1 = 0; byte byte2 = 0; byteId++; NormalizedToBytes_16(left[i], k, out byte1, out byte2); writer.Write(byte1); writer.Write(byte2); if (right != null) { byteId++; NormalizedToBytes_16(right[i], k, out byte1, out byte2); writer.Write(byte1); writer.Write(byte2); } } } } // Convert two bytes to one double in the range -1 to 1 static float BytesToNormalized_16(byte firstByte, byte secondByte) { // convert two bytes to one short (little endian) short s = (short)((secondByte << 8) | firstByte); // convert to range from -1 to (just below) 1 return s / 32678f; } // Convert a float value into two bytes (use k as conversion value and not Int16.MaxValue to avoid peaks) static void NormalizedToBytes_16(float value, float k, out byte firstByte, out byte secondByte) { short s = (short)(value * k); firstByte = (byte)(s & 0x00FF); secondByte = (byte)(s >> 8); }