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Posted 6 May 2012


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C# Speech to Text

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4.99/5 (54 votes)
7 May 2012CPOL3 min read
This article describes how to handle and use the SpeechRecognitionEngine class that is shipped with and since .NET 3.0.

speech to text application


The purpose of this article is it to give you a small insight of the capabilities of the System.Speech assembly. In detail, the usage of the SpeechRecognitionEngine class. The MSDN documentation of the class can be found here.


I read several articles about how to use Text to Speech, but as I wanted to find out how to do it the opposite way, I realized that there is a lack of easily understandable articles covering this theme, so I decided to write a very basic one on my own and share my experiences with you.

The Solution

So now let's start. First of all you need to reference the System.Speech assembly in your application located in the GAC.


This is the only reference needed containing the following namespaces and its classes. The System.Speech.Recognition namespace contains the Windows Desktop Speech technology types for implementing speech recognition.

  • System.Speech.AudioFormat
  • System.Speech.Recognition
  • System.Speech.Recognition.SrgsGrammar
  • System.Speech.Synthesis
  • System.Speech.Synthesis.TtsEngine

Before you can use SpeechRecognitionEngine, you have to set up several properties and invoke some methods: in this case I guess, code sometimes says more than words ...

// the recognition engine
SpeechRecognitionEngine speechRecognitionEngine = null;

// create the engine with a custom method (i will describe that later)
speechRecognitionEngine = createSpeechEngine("de-DE");

// hook to the needed events
speechRecognitionEngine.AudioLevelUpdated += 
  new EventHandler<AudioLevelUpdatedEventArgs>(engine_AudioLevelUpdated);
speechRecognitionEngine.SpeechRecognized += 
  new EventHandler<SpeechRecognizedEventArgs>(engine_SpeechRecognized);

// load a custom grammar, also described later

// use the system's default microphone, you can also dynamically
// select audio input from devices, files, or streams.

// start listening in RecognizeMode.Multiple, that specifies
// that recognition does not terminate after completion.

In detail now, the function createSpeechEngine(string preferredCulture). The standard constructor and its overloads are the following:

  • SpeechRecognitionEngine(): Initializes a new instance using the default speech recognizer for the system.
  • SpeechRecognitionEngine(CultureInfo): Initializes a new instance using the default speech recognizer for a specified locale.
  • SpeechRecognitionEngine(RecognizerInfo): Initializes a new instance using the information in a RecognizerInfo object to specify the recognizer to use.
  • SpeechRecognitionEngine(String): Initializes a new instance of the class with a string parameter that specifies the name of the recognizer to use.

The reason why I was creating a custom function for instantiating the class is that I wanted to add the possibility to choose the language that the engine is using. If the desired language is not installed, then the default language (Windows Desktop Language) is used. Preventing an exception while choosing a not installed package. Hint: You can install further language packs to choose a different CultureInfo that is used by the SpeechRecognitionEnginge but as far as I know, it is only supported on Win7 Ultimate/Enterprise.

private SpeechRecognitionEngine createSpeechEngine(string preferredCulture)
    foreach (RecognizerInfo config in SpeechRecognitionEngine.InstalledRecognizers())
        if (config.Culture.ToString() == preferredCulture)
            speechRecognitionEngine = new SpeechRecognitionEngine(config);

    // if the desired culture is not installed, then load default
    if (speechRecognitionEngine == null)
        MessageBox.Show("The desired culture is not installed " + 
            "on this machine, the speech-engine will continue using "
            + SpeechRecognitionEngine.InstalledRecognizers()[0].Culture.ToString() + 
            " as the default culture.", "Culture " + preferredCulture + " not found!");
        speechRecognitionEngine = new SpeechRecognitionEngine();

    return speechRecognitionEngine;

The next step is it to set up the used Grammar that is loaded by the SpeechRecognitionEngine. In our case, we create a custom text file that contains key-value pairs of texts wrapped in the custom class SpeechToText.Word because I wanted to extend the usability of the program and give you a little showcase on what is possible with SAPI. That is interesting because in doing so, we are able to associate texts or even commands to a recognized word. Here is the wrapper class SpeechToText.Word.

namespace SpeechToText
   public class Word
       public Word() { }
       public string Text { get; set; }          // the word to be recognized by the engine
       public string AttachedText { get; set; }  // the text associated with the recognized word
       public bool IsShellCommand { get; set; }  // flag determining whether this word is an command or not

Here is the method to set up the Choices used by the Grammar. In the foreach loop, we create and insert the Word classes and store them for later usage in a lookup List<Word>. Afterwards we insert the parsed words into the Choices class and finally build the Grammar by using a GrammarBuilder and load it synchronously with the SpeechRecognitionEngine. You could also simply add

s to the choices class by hand or load a predefined XML-file. Now our engine is ready to recognize the predefined words.

private void loadGrammarAndCommands()
        Choices texts = new Choices();
        string[] lines = File.ReadAllLines(Environment.CurrentDirectory + "\\example.txt");
        foreach (string line in lines)
            // skip commentblocks and empty lines..
            if (line.StartsWith("--") || line == String.Empty) continue;

            // split the line
            var parts = line.Split(new char[] { '|' });

            // add word to the list for later lookup or execution
            words.Add(new Word() { Text = parts[0], AttachedText = parts[1], 
                      IsShellCommand = (parts[2] == "true") });

            // add the text to the known choices of the speech-engine
        Grammar wordsList = new Grammar(new GrammarBuilder(texts));
    catch (Exception ex)
        throw ex;

To start the SpeechRecognitionEngine, we call SpeechRecognitionEngine.StartRecognizeAsync(RecognizeMode.Multiple). This means that the recognizer continues performing asynchronous recognition operations until the RecognizeAsyncCancel() or RecognizeAsyncStop() method is called. To retrieve the result of an asynchronous recognition operation, attach an event handler to the recognizer's SpeechRecognized event. The recognizer raises this event whenever it successfully completes a synchronous or asynchronous recognition operation.

// attach eventhandler
speechRecognitionEngine.SpeechRecognized += 
  new EventHandler<SpeechRecognizedEventArgs>(engine_SpeechRecognized);

// start recognition

// Recognized-event 
void engine_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
    txtSpoken.Text += "\r" + getKnownTextOrExecute(e.Result.Text);

And here comes the gimmick of this application, when the engine recognizes one of our predefined words, we decide whether to return the associated text, or to execute a shell command. This is done in the following function:

private string getKnownTextOrExecute(string command)
    {   // use a little bit linq for our lookup list ...
        var cmd = words.Where(c => c.Text == command).First();

        if (cmd.IsShellCommand)
            Process proc = new Process();
            proc.EnableRaisingEvents = false;
            proc.StartInfo.FileName = cmd.AttachedText;
            return "you just started : " + cmd.AttachedText;
            return cmd.AttachedText;
    catch (Exception)
        return command;

That is it! There are plenty of other possibilities to use the SAPI for, maybe a Visual Studio plug-in for coding? Let me know what ideas you guys have! I hope you enjoyed my first article.


Version release.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Sperneder Patrick
Software Developer (Senior)
Austria Austria
No Biography provided

Comments and Discussions

Questionspeech to text Pin
Member 1418516510-Nov-20 0:48
MemberMember 1418516510-Nov-20 0:48 
Questionspeech to text source code error Pin
Member 1397389014-Mar-19 21:01
MemberMember 1397389014-Mar-19 21:01 
AnswerRe: speech to text source code error Pin
minhtuanvn27-May-19 0:02
Memberminhtuanvn27-May-19 0:02 
AnswerRe: speech to text source code error Pin
ChizI28-Jul-19 11:18
MemberChizI28-Jul-19 11:18 
QuestionVoice recognition failed The language of the grammar does not match the language of speech recognition. Pin
Mohammad Kazem Hassani30-Nov-17 9:31
MemberMohammad Kazem Hassani30-Nov-17 9:31 
AnswerRe: Voice recognition failed The language of the grammar does not match the language of speech recognition. Pin
ChizI28-Jul-19 11:22
MemberChizI28-Jul-19 11:22 
QuestionLanguage Pin
Dev Windy23-Apr-17 0:01
MemberDev Windy23-Apr-17 0:01 
AnswerRe: Language Pin
minhtuanvn26-May-19 23:59
Memberminhtuanvn26-May-19 23:59 
QuestionSpeech Recognition is not working in Web application : Help Me: Emergency Pin
N4Narendran28-Jul-16 20:11
MemberN4Narendran28-Jul-16 20:11 
Questionswitching cases inside cases Pin
Frank Lopez28-Oct-15 6:21
MemberFrank Lopez28-Oct-15 6:21 
QuestionHow do you train the Engine? Pin
Member 1173386823-Sep-15 6:46
MemberMember 1173386823-Sep-15 6:46 
GeneralMy vote of 5 Pin
Santhakumar Munuswamy @ Chennai22-Jul-15 3:21
professionalSanthakumar Munuswamy @ Chennai22-Jul-15 3:21 
QuestionHow can i do it with C++ Pin
Member 1180277230-Jun-15 1:31
MemberMember 1180277230-Jun-15 1:31 
QuestionHow can this support Asian Languages like Urdu, Arabic, Farsi Pin
bootabashir16-Nov-14 18:56
Memberbootabashir16-Nov-14 18:56 
AnswerRe: How can this support Asian Languages like Urdu, Arabic, Farsi Pin
Sperneder Patrick23-Nov-14 21:55
professionalSperneder Patrick23-Nov-14 21:55 
Questiondidn't work in win7 Pin
michael nabil26-Jul-14 0:26
Membermichael nabil26-Jul-14 0:26 
AnswerRe: didn't work in win7 Pin
Sperneder Patrick26-Jul-14 4:26
professionalSperneder Patrick26-Jul-14 4:26 
GeneralRe: didn't work in win7 Pin
michael nabil26-Jul-14 22:42
Membermichael nabil26-Jul-14 22:42 
GeneralMy vote of 4 Pin
Mehmet Emin Yalçın9-Jul-14 1:22
MemberMehmet Emin Yalçın9-Jul-14 1:22 
GeneralMy vote of 4 Pin
Mehmet Emin Yalçın9-Jul-14 1:22
MemberMehmet Emin Yalçın9-Jul-14 1:22 
QuestionIt do not recognize my words correctly.. :( Pin
amol_kk8-Apr-14 2:47
Memberamol_kk8-Apr-14 2:47 
AnswerRe: It do not recognize my words correctly.. :( Pin
Sperneder Patrick5-May-14 3:11
professionalSperneder Patrick5-May-14 3:11 
AnswerRe: It do not recognize my words correctly.. :( Pin
Afzaal Ahmad Zeeshan26-Sep-14 2:24
mveAfzaal Ahmad Zeeshan26-Sep-14 2:24 
General@Sperneder-Patrick Help !! Pin
gagyy27-Feb-14 21:34
Membergagyy27-Feb-14 21:34 
Questionpopup error while executing Pin
Member 1056054510-Feb-14 1:28
MemberMember 1056054510-Feb-14 1:28 

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