How do I use a lexicon with SpeechSynthesizer?

I'm performing some text-to-speech and I'd like to specify some special pronunciations in a lexicon file. I have ran MSDN's AddLexicon example verbatim, and it speaks the sentence but it does not use the given lexicon, something appears to be broken.

Here's the provided example:

using System;

using Microsoft.Speech.Synthesis;



namespace SampleSynthesis

{

  class Program

  {

    static void Main(string[] args)

    {



      // Initialize a new instance of the SpeechSynthesizer.

      using (SpeechSynthesizer synth = new SpeechSynthesizer())

      {



        // Configure the audio output. 

        synth.SetOutputToDefaultAudioDevice();



        PromptBuilder builder = new PromptBuilder();

        builder.AppendText("Gimme the whatchamacallit.");



        // Append the lexicon file.

        synth.AddLexicon(new Uri("c:\\test\\whatchamacallit.pls"), "application/pls+xml");



        // Speak the prompt and play back the output file.

        synth.Speak(builder);

      }



      Console.WriteLine();

      Console.WriteLine("Press any key to exit...");

      Console.ReadKey();

    }

  }

}

and lexicon file:

<lexicon version="1.0" 

      xmlns="http://www.w3.org/2005/01/pronunciation-lexicon"

      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

      xsi:schemaLocation="http://www.w3.org/2005/01/pronunciation-lexicon 

        http://www.w3.org/TR/2007/CR-pronunciation-lexicon-20071212/pls.xsd"

      alphabet="x-microsoft-ups" xml:lang="en-US">





  <lexeme>

    <grapheme> whatchamacallit </grapheme>

    <phoneme> W S1 AX T CH AX M AX K S2 AA L IH T </phoneme>

  </lexeme>



</lexicon>

The console opens, the text is spoken, but the new pronunciation isn't used. I have of course saved the file to as specified.

I've tried variations of the Uri and file location (e.g. , ), absolute and relative paths, copying it into the build folder, etc.

I ran Process Monitor and the file is not accessed. If it were a directory/file permission problem (which it isn't) I would still see the access denied messages, however I log no reference at all except the occasional one from my text editor. I do see the file accessed when I try .

Unfortunately there are no error messages when using a garbage Uri.

On further investigation I realized this example is from Microsoft.Speech.Synthesis, whereas I'm using System.Speech.Synthesis over here. However from what I can tell they are identical except for some additional info and examples and both point to the same specification. Could this still be the problem?

I verified the project is set to use the proper .NET Framework 4.

I compared the example from MSDN to examples from the referenced spec, as well as trying those outright but it hasn't helped. Considering the file doesn't seem to be accessed I'm not surprised.

(I am able to use just fine but it's a poor alternative for my use case.)

Is the example on MSDN broken? How do I use a lexicon with SpeechSynthesizer?