how blocks extract from sound (audio) and convert to text?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Speech;
using System.Speech.Recognition;

namespace spechToText
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog open = new OpenFileDialog();
           // open.Filter = "AUDIO file|* .wav |file audio|* .wma";
            if(open.ShowDialog() == DialogResult.OK)
            {
              SpeechRecognitionEngine sre = new SpeechRecognitionEngine();
                Grammar gr = new DictationGrammar();
                sre.LoadGrammar(gr);
                sre.SetInputToWaveFile(open.FileName);
                sre.BabbleTimeout = new TimeSpan(Int32.MaxValue);
                sre.InitialSilenceTimeout = new TimeSpan(Int32.MaxValue);
                sre.EndSilenceTimeout = new TimeSpan(100000000);
                sre.EndSilenceTimeoutAmbiguous = new TimeSpan(100000000);

                StringBuilder sb = new StringBuilder();
                while (true)
                {
                    try
                    {
                        var recText = sre.Recognize();
                        if (recText == null)
                        {
                            break;
                        }

                        sb.Append(recText.Text);
                    }
                    catch (Exception ex)
                    {
                        //handle exception      
                        //...

                        break;
                    }
                }
                richTextBox1.AppendText( sb.ToString());

               
            
            
            
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void richTextBox1_TextChanged(object sender, EventArgs e)
        {

        }
    }
}