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SpeechRecognitionEngine.SpeechRecognitionRejected Event

Raised when the SpeechRecognitionEngine receives input that does not match any of its loaded and enabled Grammar objects.

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

public event EventHandler<SpeechRecognitionRejectedEventArgs> SpeechRecognitionRejected

The recognizer raises this event if it determines that input does not match with sufficient confidence any of its loaded and enabled Grammar objects. The Result property of the SpeechRecognitionRejectedEventArgs contains the rejected RecognitionResult object. You can use the handler for the SpeechRecognitionRejected event to retrieve recognition Alternates that were rejected and their Confidence scores.

If your application is using a SpeechRecognitionEngine instance, you can modify the confidence level at which speech input is accepted or rejected with one of the UpdateRecognizerSetting() methods. You can modify how the speech recognition responds to non-speech input using the BabbleTimeout, InitialSilenceTimeout, EndSilenceTimeout, and EndSilenceTimeoutAmbiguous properties.

When you create a SpeechRecognitionRejected delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event-handler delegates, see Events and Delegates.

The following example recognizes phrases such as "Display the list of artists in the jazz category" or "Display albums gospel". The example uses a handler for the SpeechRecognitionRejected event to display a notification in the console when the speech input cannot be matched to the contents of the grammar with sufficient Confidence to produce a successful recognition. The handler also displays recognition result Alternates that were rejected because of low confidence scores.

using System;
using Microsoft.Speech.Recognition;

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

    // Initialize a SpeechRecognitionEngine object.
    {
      using (SpeechRecognitionEngine recognizer =
         new SpeechRecognitionEngine(new System.Globalization.CultureInfo("en-US")))
      {

        // Create a grammar.
        //  Create lists of alternative choices.
        Choices listTypes = new Choices(new string[] { "albums", "artists" });
        Choices genres = new Choices(new string[] { 
          "blues", "classical", "gospel", "jazz", "rock" });

        //  Create a GrammarBuilder object and assemble the grammar components.
        GrammarBuilder mediaMenu = new GrammarBuilder("Display");
        mediaMenu.Append("the list of", 0, 1);
        mediaMenu.Append(listTypes);
        mediaMenu.Append("in the", 0, 1);
        mediaMenu.Append(genres);
        mediaMenu.Append("category", 0, 1);

        //  Build a Grammar object from the GrammarBuilder.
        Grammar mediaMenuGrammar = new Grammar(mediaMenu);
        mediaMenuGrammar.Name = "Media Chooser";

        // Attach event handlers.
        recognizer.SpeechRecognized +=
          new EventHandler<SpeechRecognizedEventArgs>(recognizer_SpeechRecognized);
        recognizer.SpeechRecognitionRejected +=
          new EventHandler<SpeechRecognitionRejectedEventArgs>(recognizer_SpeechRecognitionRejected);

        // Load the grammar object to the recognizer.
        recognizer.LoadGrammarAsync(mediaMenuGrammar);

        // Set the input to the recognizer.
        recognizer.SetInputToDefaultAudioDevice();

        // Start asynchronous, continuous recognition.
        recognizer.RecognizeAsync(RecognizeMode.Multiple);
        Console.WriteLine("Starting asynchronous recognition...");

        // Keep the console window open.
        Console.ReadLine();
      }
    }

    // Handle the SpeechRecognitionRejected event.
    static void recognizer_SpeechRecognitionRejected(object sender, SpeechRecognitionRejectedEventArgs e)
    {
      Console.WriteLine("Speech input was rejected.");
      foreach (RecognizedPhrase phrase in e.Result.Alternates)
      {
        Console.WriteLine("  Rejected phrase: " + phrase.Text);
        Console.WriteLine("  Confidence score: " + phrase.Confidence);
        Console.WriteLine("  Grammar name:  " + phrase.Grammar.Name);
      }
    }

    // Handle the SpeechRecognized event.
    static void recognizer_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
    {
      Console.WriteLine("Speech recognized: " + e.Result.Text);
      Console.WriteLine("  Confidence score: " + e.Result.Confidence);
    }
  }
}

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