参考記事

C#での音声認識は、手軽く、精度もそこそこに、既存のマイクで行うことが出来る(霊的な引用を、あなたの心に届けよう)。 - Qiita

コンパイル用バッチ

compile.bat


csc /r:C:\Windows\Microsoft.NET\assembly\GAC_MSIL\System.Speech\v4.0_4.0.0.0__31bf3856ad364e35\System.Speech.dll ^
 %*

サンプルプログラム

めもちょう
ぺいんと
きゃぷちゃ

とマイクに話しかけると、登録したプログラムが起動します。
（myActions変数に登録したラムダ式を、MMFrame.Media.SpeechRecognition.SpeechRecognizedEventイベント発生時に呼び出している。）


using System;
using System.Collections.Generic;
using System.IO;
using System.Windows.Forms;

using System.Speech.Recognition;


namespace MMFrame.Media
{
    public static class SpeechRecognition
    {
        public static SpeechRecognitionEngine Engine;

        public static bool IsAvailable
        {
            get { return (Engine != null && !IsDestroyed); }
        }

        public static bool IsRecognizing
        {
            get { return (IsAvailable && Engine.AudioState != AudioState.Stopped); }
        }

        public static System.Collections.ObjectModel.ReadOnlyCollection<RecognizerInfo> InstalledRecognizers
        {
            get { return SpeechRecognitionEngine.InstalledRecognizers(); }
        }

        //public static System.Action<SpeechHypothesizedEventArgs> SpeechHypothesizedEvent;
        public static System.Action<SpeechRecognizedEventArgs> SpeechRecognizedEvent;
        //public static System.Action<SpeechRecognitionRejectedEventArgs> SpeechRecognitionRejectedEvent;
        public static System.Action<RecognizeCompletedEventArgs> SpeechRecognizeCompletedEvent;

        private static bool IsDestroyed;

        static SpeechRecognition()
        {
            IsDestroyed = true;
        }

        public static void DestroyEngine()
        {
            if (!IsAvailable) { return; }

            //Engine.SpeechHypothesized -= SpeechHypothesized;
            Engine.SpeechRecognized -= SpeechRecognized;
            //Engine.SpeechRecognitionRejected -= SpeechRecognitionRejected;
            Engine.RecognizeCompleted -= SpeechRecognizeCompleted;
            Engine.UnloadAllGrammars();
            Engine.Dispose();

            IsDestroyed = true;
        }

        public static void AddGrammar(string grammarName, params string[] words)
        {
            Choices choices = new Choices();
            choices.Add(words);

            GrammarBuilder grammarBuilder = new GrammarBuilder();
            grammarBuilder.Append(choices);

            Grammar grammar = new Grammar(grammarBuilder) {
                Name = grammarName
            };

            if (!IsAvailable) { return; }

            Engine.LoadGrammar(grammar);
        }

        public static void ClearGrammar()
        {
            if (!IsAvailable) { return; }

            Engine.UnloadAllGrammars();
        }

        public static void RecognizeAsync(bool multiple)
        {
            if (IsRecognizing || Engine.Grammars.Count <= 0) {
                return;
            }

            RecognizeMode mode = (multiple) ? RecognizeMode.Multiple : RecognizeMode.Single;
            Engine.RecognizeAsync(mode);
        }

        public static void RecognizeAsyncCancel()
        {
            if (!IsRecognizing) { return; }

            Engine.RecognizeAsyncCancel();
        }

        public static void RecognizeAsyncStop()
        {
            if (!IsRecognizing) { return; }

            Engine.RecognizeAsyncStop();
        }

        public static void CreateEngine()
        {
            if (IsAvailable) { return; }

            Engine = new SpeechRecognitionEngine();

            IsDestroyed = false;

            Engine.SetInputToDefaultAudioDevice();

            //Engine.SpeechHypothesized += SpeechHypothesized;
            Engine.SpeechRecognized += SpeechRecognized;
            //Engine.SpeechRecognitionRejected += SpeechRecognitionRejected;
            Engine.RecognizeCompleted += SpeechRecognizeCompleted;
        }

        private static void SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
        {
            if (e.Result != null && SpeechRecognizedEvent != null) {
                SpeechRecognizedEvent(e);
            }
        }

        private static void SpeechRecognizeCompleted(object sender, RecognizeCompletedEventArgs e)
        {
            if (e.Result != null && SpeechRecognizeCompletedEvent != null) {
                SpeechRecognizeCompletedEvent(e);
            }
        }
    }
}

namespace TestClass
{
    public class Form1 : System.Windows.Forms.Form
    {
        Dictionary<string,Action> myActions;

        public Form1()
        {
            myActions = new Dictionary<string,Action>();
            myActions.Add("めもちょう", ()=>{
                var pInfo = new System.Diagnostics.ProcessStartInfo();
                pInfo.FileName = "notepad";
                System.Diagnostics.Process.Start(pInfo);
            });
            myActions.Add("ぺいんと", ()=>{
                var pInfo = new System.Diagnostics.ProcessStartInfo();
                pInfo.FileName = "mspaint";
                System.Diagnostics.Process.Start(pInfo);
            });
            myActions.Add("きゃぷちゃ", ()=>{
                var pInfo = new System.Diagnostics.ProcessStartInfo();
                pInfo.FileName = "snippingtool";
                System.Diagnostics.Process.Start(pInfo);
            });
            myActions.Add("だみー", ()=>{
            });

            MMFrame.Media.SpeechRecognition.CreateEngine();

            foreach (RecognizerInfo ri in MMFrame.Media.SpeechRecognition.InstalledRecognizers) {
                Console.WriteLine(ri.Name + "(" + ri.Culture + ")");
            }

            MMFrame.Media.SpeechRecognition.SpeechRecognizedEvent = (e) =>
            {
                Console.WriteLine("確定：" + e.Result.Grammar.Name + " " + e.Result.Text + "(" + e.Result.Confidence + ")");

                if (myActions.ContainsKey(e.Result.Text)) {
                    Action act = myActions[e.Result.Text];
                    act();
                }
            };

            MMFrame.Media.SpeechRecognition.SpeechRecognizeCompletedEvent = (e) =>
            {
                if (e.Cancelled) {
                    Console.WriteLine("キャンセルされました。");
                }

                Console.WriteLine("認識終了");
            };

            Load += (s,e)=>{
                AddGrammar();
                MMFrame.Media.SpeechRecognition.RecognizeAsync(true); // falseにすると、一回認識すると終了する
            };

            Closed += (s,e)=>{
                //MMFrame.Media.SpeechRecognition.ClearGrammar();
                MMFrame.Media.SpeechRecognition.RecognizeAsyncCancel();
                MMFrame.Media.SpeechRecognition.RecognizeAsyncStop();
                MMFrame.Media.SpeechRecognition.DestroyEngine();
            };
        }

        private void AddGrammar()
        {
            var tmp = myActions.Keys;
            string[] words = new string[tmp.Count]; //new string[] { "めもちょう","ぺいんと" };
            tmp.CopyTo(words,0);
            MMFrame.Media.SpeechRecognition.AddGrammar("words", words);
        }

        static void Main(string[] args)
        {
            Application.Run(new Form1());
        }
    }
}

注意点

わりと誤認識したりするので、処理内容は慎重に決めましょう。

追記(2021.01.27)

ちなみに事前のキーワード指定なし(AddGrammarなし)だと絶望的に誤認識します。下記にサンプルコード置いときます。
（エアコンの音をひろって、なぞの笑い声を検出してました。。。）
ちなみに日本語だからイマイチなわけではなく、英語もダメっぽいです。（デフォルトだと日本語しかサポートしてなかったのでStoreでわざわざインストールしてみましたがイマイチ。。）

参考サイト

サンプルプログラム

上記サイト1のコードを参考にVisualStudioなしでも動くようにしたもの。（簡単のためWinForms形式にしてます。）


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

public class MainForm : Form
{
    SpeechRecognitionEngine engine;

    public MainForm()
    {
        Button btn = new Button(){};
        Controls.Add(btn);

        var infoCollection = SpeechRecognitionEngine.InstalledRecognizers();
        foreach (RecognizerInfo info in infoCollection) {
            Console.WriteLine("----");
            Console.Write("desc: ");
            Console.WriteLine(info.Description);
            Console.Write("DisplayName: ");
            Console.WriteLine(info.Culture.DisplayName);
        }

        btn.Click += (s,e)=>{
            engine = new SpeechRecognitionEngine();
            //engine = new SpeechRecognitionEngine(new System.Globalization.CultureInfo("en-US"));
            engine.SpeechRecognized += EngineSpeechRecognized;//認識処理
            engine.SpeechHypothesized += EngineSpeechHypothesized;//推定処理
            engine.LoadGrammar(new DictationGrammar());//ディクテーション用の辞書
            engine.SetInputToDefaultAudioDevice();//エンジンの入力
            engine.RecognizeAsync(RecognizeMode.Multiple);//開始
        };
    }

    private void EngineSpeechHypothesized(object sender, SpeechHypothesizedEventArgs e)
    {
        //Console.Write("Hypo: ");
        //Console.WriteLine(e.Result.Text);
    }

    private void EngineSpeechRecognized(object sender, SpeechRecognizedEventArgs e)
    {
        Console.Write("Recg: ");
        Console.WriteLine(e.Result.Text);
    }

    [STAThread]
    static void Main(string[] args)
    {
        Application.Run(new MainForm());
    }
}

C#でWindows標準の音声認識で遊んでみた

参考記事

コンパイル用バッチ

サンプルプログラム

注意点

追記(2021.01.27)

参考サイト

サンプルプログラム