How to use the DTMFRecognitionEngine class in Microsoft.Speech

Question

The Microsoft.Speech SDK has a DTMFRecognitionEngine class, which I'd like to experiment with - we need to detect DTMF tones within a WAV file (I realise there are other ways to do this, but I'm evaluating all possible methods).

The documentation isn't clear on how to actually use the class: it's companion class, SpeechRecognitionEngine, has plenty of examples and nice clear methods like SetInputToWaveFile. DTMFRecognitionEngine doesn't have any such methods.

Could someone provide insight on how I can use this component in my own code?

EDIT: It appears that there isn't any way to use this class for ... well, anything much really. I'm looking for a library that will allow me to detect the position and duration of DTMF digits in an audio file. I've looked at TapiEx, but they're not responding to emails. If anyone has any other suggestions, they'd be gratefully received...

Answer 1

It would appear that this is not possible. I even went so far as to get the private _engine of DtmfRecognitionEngine which is a wrapper the SpeechRecognitionEngine and call its SetInputToWaveFile with no luck. Apparently the only way to get a tone into the DtmfRecognitionEngine is to call AddTone(). I've included a sample grammar file and some source code that you can play with. Interestingly, if you uncomment the dre.AddTone()'s you see both sre's events and dre's events are getting fired.

Switching the call to sre.RecognizeAsync() does not help.

Looks like you'll need a different library...

PinGrammar.xml

<?xml version="1.0"?>
<grammar mode="dtmf" version="1.0"
         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"
         xmlns="http://www.w3.org/2001/06/grammar"
         root="pin">

  <rule id="digit">
    <one-of>
      <item> 0 </item>
      <item> 1 </item>
      <item> 2 </item>
      <item> 3 </item>
      <item> 4 </item>
      <item> 5 </item>
      <item> 6 </item>
      <item> 7 </item>
      <item> 8 </item>
      <item> 9 </item>
    </one-of>
  </rule>

  <rule id="pin" scope="public">
    <one-of>
      <item>
        <item repeat="4">
          <ruleref uri="#digit"/>
        </item>
        #
      </item>
      <item>
        * 9
      </item>
    </one-of>
  </rule>

</grammar>

Source:

using Microsoft.Speech.Recognition;
using System.Reflection;

namespace DTMF_Recognition
{
    class Program
    {
        static void Main(string[] args)
        {
            Grammar grammar = null;
            grammar = new Grammar("PinGrammar.xml");

            DtmfRecognitionEngine dre = new DtmfRecognitionEngine();
            dre.DtmfRecognized += dre_DtmfRecognized;

            FieldInfo field = typeof(DtmfRecognitionEngine).GetField("_engine", BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Instance);
            var wrapper = field.GetValue(dre);
            FieldInfo engineField = wrapper.GetType().GetField("_engine", BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Instance);
            SpeechRecognitionEngine sre = (SpeechRecognitionEngine)engineField.GetValue(wrapper);

            dre.DtmfHypothesized += dre_DtmfHypothesized;
            dre.DtmfRecognitionRejected += dre_DtmfRecognitionRejected;
            dre.RecognizeCompleted += dre_RecognizeCompleted;
            dre.LoadGrammar(grammar);

            //dre.AddTone(DtmfTone.One);
            //dre.AddTone(DtmfTone.Two);
            //dre.AddTone(DtmfTone.Three);
            //dre.AddTone(DtmfTone.Four);
            //dre.AddTone(DtmfTone.Hash);

            sre.SetInputToWaveFile(@"C:\Users\Clay Ver Valen\Desktop\3.wav");
            sre.SpeechHypothesized += sre_SpeechHypothesized;
            sre.SpeechDetected += sre_SpeechDetected;
            sre.SpeechRecognitionRejected += sre_SpeechRecognitionRejected;

            dre.RecognizeAsync();
            System.Threading.Thread.Sleep(30000);
        }

        static void sre_SpeechRecognitionRejected(object sender, SpeechRecognitionRejectedEventArgs e)
        {
            int i = 1;
        }

        static void sre_SpeechHypothesized(object sender, SpeechHypothesizedEventArgs e)
        {
            int i = 1;
        }

        static void sre_SpeechDetected(object sender, SpeechDetectedEventArgs e)
        {
            int i = 1;
        }

        static void dre_DtmfRecognitionRejected(object sender, DtmfRecognitionRejectedEventArgs e)
        {
            int i = 1;
        }

        static void dre_DtmfHypothesized(object sender, DtmfHypothesizedEventArgs e)
        {
            int i = 1;
        }

        static void dre_RecognizeCompleted(object sender, DtmfRecognizeCompletedEventArgs e)
        {
            int i = 1;
        }

        static void dre_DtmfRecognized(object sender, DtmfRecognizedEventArgs e)
        {
            int i = 1;
        }
    }
}