Prodigy Productions, LLC

By request from a couple of my readers, I am back to show more speech recognition using C#. In my first speech recognition article “Simple Speech Recognition Using C#“, I introduced you to the Speech Recognition Engine provided by the .NET framework. In that article, I showed you how to setup a new SRE and to accept any voice input and display it in a rich text box. The very next day, I took that application one step further in my article “Simple Speech Recognition Using C# – Part 2” by introducing you to grammars. Grammars are basically a list of input options you want your application to listen for. Adding grammars will cause your application to listen for only those options and nothing else. The grammar used in that article was built using the Choices object and by providing that object with a list of hardcoded options. Today, I want to show you how to replace the Choices object with a grammar XML file. Let’s begin.

The first thing you are going to need for this is of course your grammar file.  The grammar file is simply an XML file that contains a list of rules where each rule has a list of items that the SRE will listen for. Each rule must contain an id which will be used to tell the SRE which list of options to listen for. In the example below, you will see that I have defined 2 rules. You will also notice that I have added a scope attribute with the value “public” to each rule. If you do not specify the “root” attribute in the first “<grammar>” tag of your XML file, you will need to add a public scope to your rules, otherwise your SRE will not be able to read the rules.

<grammar xmlns="http://www.w3.org/2001/06/grammar"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.w3.org/2001/06/grammar http://www.w3.org/TR/speech-grammar/grammar.xsd"
  xml:lang="en-US" version="1.0" root="command1">

  <rule id="command1" scope="public">
    <one-of>
      <item>start</item>
      <item>stop</item>
      <item>continue</item>
    </one-of>
  </rule>

  <rule id="command2" scope="public">
    <one-of>
      <item>test</item>
      <item>help</item>
      <item>hello</item>
    </one-of>
  </rule>

</grammar>

For this example, we are going to be using the first rule from our grammar XML file. In order for us to do that, we’ll need to create a new SpeechRecognitionEngine, tell it which audio device to use, and give it a callback handler where the recognized text will be processed and handled. To keep it simple, we’ll just copy the construction of our SRE from our other articles.

            SpeechRecognitionEngine recognitionEngine = new SpeechRecognitionEngine();
            recognitionEngine.SetInputToDefaultAudioDevice();
            recognitionEngine.SpeechRecognized += (s, args) =>
            {
                foreach (RecognizedWordUnit word in args.Result.Words)
                {
                    // You can change the minimun confidence level here
                    if (word.Confidence > 0.8f)
                        freeTextBox.Text += word.Text + " ";
                }
                freeTextBox.Text += Environment.NewLine;
            };

Now that we have our SRE constructed, it’s time to build our Grammar object. In the last article, you will that we built a new GrammarBuilder object and constructed our Grammar object using this grammar builder. This time, we’re going to replace that grammar builder with a string indicating the name of the grammar XML file we’ll be using. After that, we’ll go ahead and load our grammar object into our SRE and tell it to begin listening by calling the RecognizeAsync method like we did in the other articles.

            Grammar g = new Grammar("grammar.xml", "command1");
            recognitionEngine.LoadGrammar(g);
            recognitionEngine.RecognizeAsync(RecognizeMode.Multiple);

In the snippet above, you’ll see that I passed 2 arguments to my Grammar object’s constructor. The first parameter is the name of the XML file that contains my grammar rules. The second parameter is the id of the rule I want to use from that XML file. If you want to omit the second parameter, you will need to include the “root” parameter on the “<grammar>” element of your XML file. If you do that, the first element of your XML file would look like:

<grammar …. root=”command1″>

That’s it! You are now ready to start using your grammar XML file in your SRE application. Here is a screenshot of the code below in action.

And, here is the complete code I used to make this happen.

using System;
using System.Text;
using System.Windows.Forms;
using System.Speech.Recognition;

namespace SpeechRecognition
{
    public partial class MainForm : Form
    {
        public MainForm()
        {
            InitializeComponent();

            SpeechRecognitionEngine recognitionEngine = new SpeechRecognitionEngine();
            recognitionEngine.SetInputToDefaultAudioDevice();
            recognitionEngine.SpeechRecognized += (s, args) =>
            {
                foreach (RecognizedWordUnit word in args.Result.Words)
                {
                    // You can change the minimun confidence level here
                    if (word.Confidence > 0.8f)
                        freeTextBox.Text += word.Text + " ";
                }
                freeTextBox.Text += Environment.NewLine;
            };

            Grammar g = new Grammar("grammar.xml", "command1");
            recognitionEngine.LoadGrammar(g);
            recognitionEngine.RecognizeAsync(RecognizeMode.Multiple);
        }
    }
}

Related Posts

• C# Woot! Off Notifier
• Augmented Reality Using C# and OpenCV
• Scan Wireless (WiFi) Networks Using C#
• Wireless Communication with XBee and C#
• Detect Your Own Objects with OpenCV and C#