2006
12.20

quickie notes on Vista speech recognition through System.Speech (.NET 3.0)

Category: .net, microsoft / Tags: no tag / Add Comment

Just to play around with it, I wrote a quickie app to call the .NET 3.0 interfaces for Vista’s speech recognition.  In particular, it accepts a .wav file as a param and just has the recognition engine run over that.

Some quick notes:

  • The default recognition engine isn’t necessarily the one you want.
  • On my system, I have 3 installed, one of which is the one from Office 2003 (still installed on the machine).  This appears to be the one I’m getting by default when I don’t specifically specify the recognizer to use.  Calling SpeechRecognitionEngine.InstalledRecognizers() gives, for me:
  • Installed recognizer: MS-1033-61-DESK [Microsoft English (U.S.) v6.1 Recognizer]  <– this is likely the one from Office 2003, and is the one I got by default
  • Installed recognizer: MS-1033-80-DESK [Microsoft Speech Recognizer 8.0 for Windows (English - US)]
  • Installed recognizer: MS-2057-80-DESK [Microsoft Speech Recognizer 8.0 for Windows (English - UK)]
  • When I’m constructing the SpeechRecognitionEngine, using “MS-1033-80-DESK” for the recognizerId string works fine and gets me the recognition I expect.
  • The API seems to assume you want call Recognize or RecognizeAsync multiple times.
  • While looping, there’s no way to check when to end (when to stop calling Recognize) except for checking when you get an InvalidOperationException.  Here’s some quickie PowerShell showing 2 valid calls and then the invalid one once we reach the end of the (short) wav file.  I really hate how end-of-file is an exception since it’s NOT an exceptional condition (at least in the pre-recorded audio sense – I understand why it is for a microphone).
    • C:\> [void][reflection.assembly]::loadwithpartialname(’system.speech’)
      C:\> $rec = new-object ‘System.Speech.Recognition.SpeechRecognitionEngine’
      C:\> $rec.RecognizerInfo.Description
      Microsoft Speech Recognizer 8.0 for Windows (English – US)
      C:\> $rec.LoadGrammar((new-object ‘System.Speech.Recognition.DictationGrammar’))
      C:\> $rec.SetInputToWaveFile(‘C:\Documents and Settings\admin\Desktop\downloads\test.wav’)
      C:\> $rec.Recognize() | fl text,confidence

      • Text : This is a test 12345678
      Confidence : 0.6058533

      C:\> $rec.Recognize() | fl text,confidence

      Text : 910 this was a test
      Confidence : 0.6938771

      C:\> $rec.Recognize() | fl text,confidence
      Exception calling “Recognize” with “0″ argument(s): “No audio input is supplied to this recognizer. Use the method SetInputToDefaultAudioDevice if a microphone is connected to the system, otherwise use SetInputToWaveFile, SetInputToWaveStream or SetInputToAudioStream to perform speech recognition from pre-recorded audio.”
      At line:1 char:15
      + $rec.Recognize( <<<< ) | fl text,confidence
      C:\> $error[0].exception.innerexception.gettype().name
      InvalidOperationException
      C:\>

  • Recognition on “bad” input may actually return null from Recognize (and depending on the size of the file, may block for quite awhile).  Here’s a normal (comes with Vista) wav file.  It doesn’t have any actual speech in it.
    C:\> dir $env:windir\media\start.wav
    Directory: Microsoft.PowerShell.Core\FileSystem::C:\Windows\media
    Mode  LastWriteTime     Length Name
    —-  ————-     —— —-
    -a— 8/23/2001 8:00 AM   1192 start.wav
    • Here’s recognition on that file returning null
      C:\> $rec.SetInputToWaveFile(“$env:windir\media\start.wav”)
      C:\> $output = $rec.Recognize()
      C:\> $output -eq $null
      True
    1. marta rinaldi said: 2007.06.04 23:22

      I want to know if you have this program in spanish. thank you.

    2. Adarsh said: 2007.10.06 13:10

      Hi
      I tried to convert a wav file into text but the accuracy is terrible. Is there any way to improve the accuracy.

      Thanks and Regards,
      Adarsh Nagaraj

    3. Stephanie said: 2009.02.17 00:40

      Did you ever get it to read all the input from a wav file and not have it throw exceptions all over the place/