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SpeechRecognitionEngine.SpeechDetected Event

Raised when the SpeechRecognitionEngine detects input that it can identify as speech.

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

member SpeechDetected : IEvent<EventHandler<SpeechDetectedEventArgs>,
    SpeechDetectedEventArgs>

Each speech recognizer has an algorithm to distinguish between silence and speech. When the SpeechRecognitionEngine performs a speech recognition operation, it raises the SpeechDetected event when its algorithm identifies the input as speech. The AudioPosition property of the associated SpeechDetectedEventArgs object indicates location in the input stream where the recognizer detected speech. The SpeechRecognitionEngine raises the SpeechDetected event before it raises any of the SpeechHypothesized, SpeechRecognized, or SpeechRecognitionRejected events.

For more information see the Recognize, RecognizeAsync, EmulateRecognize, and EmulateRecognizeAsync methods.

When you create a SpeechDetected 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 is part of a console application for choosing origin and destination cities for a flight. The application recognizes phrases such as "I want to fly from Miami to Chicago." The example uses the SpeechDetected event to report the AudioPosition each time speech is detected.

using System;
using System.Speech.Recognition;

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

    // Initialize an in-process speech recognition engine.
    {
      using (SpeechRecognitionEngine recognizer =
         new SpeechRecognitionEngine())
      {

        // Create a grammar.
        Choices cities = new Choices(new string[] { 
          "Los Angeles", "New York", "Chicago", "San Francisco", "Miami", "Dallas" });

        GrammarBuilder gb = new GrammarBuilder();
        gb.Append("I would like to fly from");
        gb.Append(cities);
        gb.Append("to");
        gb.Append(cities);

        // Create a Grammar object and load it to the recognizer.
        Grammar g = new Grammar(gb);
        g.Name = ("City Chooser");
        recognizer.LoadGrammarAsync(g);

        // Attach event handlers.
        recognizer.LoadGrammarCompleted +=
          new EventHandler<LoadGrammarCompletedEventArgs>(recognizer_LoadGrammarCompleted);
        recognizer.SpeechDetected +=
          new EventHandler<SpeechDetectedEventArgs>(recognizer_SpeechDetected);
        recognizer.SpeechRecognized +=
          new EventHandler<SpeechRecognizedEventArgs>(recognizer_SpeechRecognized);

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

        // Start recognition.
        recognizer.RecognizeAsync();

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

    // Handle the SpeechDetected event.
    static void recognizer_SpeechDetected(object sender, SpeechDetectedEventArgs e)
    {
      Console.WriteLine("  Speech detected at AudioPosition = {0}", e.AudioPosition);
    }

    // Handle the LoadGrammarCompleted event.
    static void recognizer_LoadGrammarCompleted(object sender, LoadGrammarCompletedEventArgs e)
    {
      Console.WriteLine("Grammar loaded: " + e.Grammar.Name);
    }

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

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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