SpeechRecognitionEngine.InitialSilenceTimeout Property


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Gets or sets the time interval during which a SpeechRecognitionEngine accepts input containing only silence before finalizing recognition.

Namespace:   System.Speech.Recognition
Assembly:  System.Speech (in System.Speech.dll)

public TimeSpan InitialSilenceTimeout { get; set; }

Property Value

Type: System.TimeSpan

The duration of the interval of silence.

Exception Condition

This property is set to less than 0 seconds.

Each speech recognizer has an algorithm to distinguish between silence and speech. If the recognizer input is silence during the initial silence timeout period, then the recognizer finalizes that recognition operation.

If the initial silence timeout interval is set to 0, the recognizer does not perform an initial silence timeout check. The timeout interval can be any non-negative value. The default is 0 seconds.

The following example shows part of a console application that demonstrates basic speech recognition. The example sets the BabbleTimeout and InitialSilenceTimeout properties of a SpeechRecognitionEngine before initiating speech recognition. Handlers for the speech recognizer's AudioStateChanged and RecognizeCompleted events output event information to the console to demonstrate how the InitialSilenceTimeout properties of a SpeechRecognitionEngine properties affect recognition operations.

using System;
using System.Speech.Recognition;

namespace SpeechRecognitionApp
  class Program
    static void Main(string[] args)

      // Initialize an in-process speech recognizer.
      using (SpeechRecognitionEngine recognizer =
        new SpeechRecognitionEngine(
          new System.Globalization.CultureInfo("en-US")))
        // Load a Grammar object.

        // Add event handlers.
        recognizer.AudioStateChanged +=
          new EventHandler<AudioStateChangedEventArgs>(
        recognizer.RecognizeCompleted +=
          new EventHandler<RecognizeCompletedEventArgs>(

        // Configure input to the speech recognizer.

        recognizer.InitialSilenceTimeout = TimeSpan.FromSeconds(3);
        recognizer.BabbleTimeout = TimeSpan.FromSeconds(2);
        recognizer.EndSilenceTimeout = TimeSpan.FromSeconds(1);
        recognizer.EndSilenceTimeoutAmbiguous = TimeSpan.FromSeconds(1.5);

        Console.WriteLine("BabbleTimeout: {0}", recognizer.BabbleTimeout);
        Console.WriteLine("InitialSilenceTimeout: {0}", recognizer.InitialSilenceTimeout);
        Console.WriteLine("EndSilenceTimeout: {0}", recognizer.EndSilenceTimeout);
        Console.WriteLine("EndSilenceTimeoutAmbiguous: {0}", recognizer.EndSilenceTimeoutAmbiguous);

        // Start asynchronous speech recognition.

        // Keep the console window open.
        while (true)

    // Create a grammar and build it into a Grammar object. 
    static Grammar CreateServicesGrammar(string grammarName)

      // Create a grammar for finding services in different cities.
      Choices services = new Choices(new string[] { "restaurants", "hotels", "gas stations" });
      Choices cities = new Choices(new string[] { "Seattle", "Boston", "Dallas" });

      GrammarBuilder findServices = new GrammarBuilder("Find");

      // Create a Grammar object from the GrammarBuilder..
      Grammar servicesGrammar = new Grammar(findServices);
      servicesGrammar.Name = ("FindServices");
      return servicesGrammar;

    // Handle the AudioStateChanged event.
    static void AudioStateChangedHandler(
      object sender, AudioStateChangedEventArgs e)
      Console.WriteLine("AudioStateChanged ({0}): {1}",
        DateTime.Now.ToString("mm:ss.f"), e.AudioState);

    // Handle the RecognizeCompleted event.
    static void RecognizeCompletedHandler(
      object sender, RecognizeCompletedEventArgs e)
      Console.WriteLine("RecognizeCompleted ({0}):",

      string resultText;
      if (e.Result != null) { resultText = e.Result.Text; }
      else { resultText = "<null>"; }

        " BabbleTimeout: {0}; InitialSilenceTimeout: {1}; Result text: {2}",
        e.BabbleTimeout, e.InitialSilenceTimeout, resultText);
      if (e.Error != null)
        Console.WriteLine(" Exception message: ", e.Error.Message);

      // Start the next asynchronous recognition operation.

.NET Framework
Available since 3.0
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