juntar arquivos .wav com ASP.NET Core (C#)

Question

Prezados, por favor

Estou tentando mesclar três arquivos .wav, mas sempre um dos arquivos no final é acelerado e distorcido (como se tivesse sendo reproduzido de maneira acelerada). 

string[] files = new string[3] { @"1.wav", @"2.wav", @"3.wav" };

WaveIO wa = new WaveIO();
wa.Merge(files, @"4.wav");

Join class:

class WaveIO
        {
            public int length;
            public short channels;
            public int samplerate;
            public int DataLength;
            public short BitsPerSample;

            private void WaveHeaderIN(string spath)
            {
                FileStream fs = new FileStream(spath, FileMode.Open, FileAccess.Read);

                BinaryReader br = new BinaryReader(fs);
                length = (int)fs.Length - 8;
                fs.Position = 22;
                channels = br.ReadInt16();
                fs.Position = 24;
                samplerate = br.ReadInt32();
                fs.Position = 34;

                BitsPerSample = br.ReadInt16();
                DataLength = (int)fs.Length - 44;
                br.Close();
                fs.Close();

            }

            private void WaveHeaderOUT(string sPath)
            {
                FileStream fs = new FileStream(sPath, FileMode.Create, FileAccess.Write);

                BinaryWriter bw = new BinaryWriter(fs);
                fs.Position = 0;
                bw.Write(new char[4] { 'R', 'I', 'F', 'F' });

                bw.Write(length);

                bw.Write(new char[8] { 'W', 'A', 'V', 'E', 'f', 'm', 't', ' ' });

                bw.Write((int)16);

                bw.Write((short)1);
                bw.Write(channels);

                bw.Write(samplerate);

                bw.Write((int)(samplerate * ((BitsPerSample * channels) / 8)));

                bw.Write((short)((BitsPerSample * channels) / 8));

                bw.Write(BitsPerSample);

                bw.Write(new char[4] { 'd', 'a', 't', 'a' });
                bw.Write(DataLength);
                bw.Close();
                fs.Close();
            }
            public void Merge(string[] files, string outfile)
            {
                WaveIO wa_IN = new WaveIO();
                WaveIO wa_out = new WaveIO();

                wa_out.DataLength = 0;
                wa_out.length = 0;


                //Gather header data
                foreach (string path in files)
                {
                    wa_IN.WaveHeaderIN(@path);
                    wa_out.DataLength += wa_IN.DataLength;
                    wa_out.length += wa_IN.length;

                }

                //Recontruct new header
                wa_out.BitsPerSample = wa_IN.BitsPerSample;
                wa_out.channels = wa_IN.channels;
                wa_out.samplerate = wa_IN.samplerate;
                wa_out.WaveHeaderOUT(@outfile);

                foreach (string path in files)
                {
                    FileStream fs = new FileStream(@path, FileMode.Open, FileAccess.Read);
                    byte[] arrfile = new byte[fs.Length - 44];
                    fs.Position = 44;
                    fs.Read(arrfile, 0, arrfile.Length);
                    fs.Close();

                    FileStream fo = new FileStream(@outfile, FileMode.Append, FileAccess.Write);
                    BinaryWriter bw = new BinaryWriter(fo);
                    bw.Write(arrfile);
                    bw.Close();
                    fo.Close();
                }
            }


        }

O que poderia estar acontecendo?

Muito obrigado,

Eu tentei, mas sem sucesso:
- https://stackoverflow.com/questions/6777340/how-to-join-2-or-more-wav-files-together-programmatically
- https://stackoverflow.com/questions/340646/how-to-concatenate-wav-files-in-c-sharp
- https://www.codeproject.com/Articles/35725/C-WAV-file-class-audio-mixing-and-some-light-audio