Programming Speech in WPF - Speech Synthesis

Mahesh Chand
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The new Microsoft Speech API (SAPI) version 5.3, which is an integral part of Windows Vista, is a managed API that allows developers to write speech-enable applications in .NET Framework 3.0. This speech functionality is defined in the System.Speech and its five sub namespaces. Physically, the speech API resides in System.Speech.Dll assembly.

Here is a list of the five namespaces that defines the Speech-related functionality:

System.Speech.Audioformat
System.Speech.Recognition
System.Speech.Recognition.SrgsGrammar
System.Speech.Synthesis
System.Speech.Synthesis.TtsEngine

To access the Speech API in WPF, you must add a System.Speech.Dll assembly reference to a project. Right-click on the project name in Solution Explorer, select Add Reference and select System.Speech on the .NET Tab and select OK button as shown in Figure 1.

Figure 1.

This action will add a System.Speech assembly reference and copy the System.Speech.dll to the bin folder of your project. Now you can import the System.Speech related namespaces to your application.

Speech Synthesis

Speech Synthesis, also known as text-to-speech in previous versions of SAPI, is a process of converting text to speech.

Windows Vista comes with a default voice called Microsoft Anna. Let's have a look at it. Go to the Control Panel and click on Text to Speech. You will see the Speech Properties dialog with two tabs, "Text to Speech" and "Speech Recognition" as you can see in Figure 2 and Figure 3.

Figure 2.

In the Text to Speech dialog box, you will see a Voice Selection dropdown showing Microsoft Anna. In this dialog, you may also test the voice and audio output. If you have more voices installed, you will see them in the dropdown list as well. You can install more voices when you install Microsoft Speech SDK. 5.1.

Figure 3.

Table 1 describes the classes available in the System.Speech.Synthesis namespace.

Class	Description
FilePrompt	Represents a prompt spoken from a file.
InstalledVoice	Represents an installed Voice object.
Prompt	Plays a prompt from text or from a PromptBuilder.
PromptBuilder	Creates an empty Prompt object and provides methods for adding content.
PromptStyle	Defines a style of prompting that consists of settings for emphasis, rate, and volume.
SpeechSynthesizer	Supports the production of speech and DTMF output.
VoiceInfo	Represents a text-to-speech (TTS) voice.

In this article, our focus is on the SpeechSynthesizer class and its methods and properties.

SpeechSynthesizer

The SpeechSynthesizer generates text to speech.

The Speak method speaks the text synchronously. The following code creates a SpeechSynthesizer object and calls the Speak method that says "Hello WPF.". By default, the SpeechSynthesizer uses the Microsoft Mary voice.

SpeechSynthesizer ss = new SpeechSynthesizer();

ss.Speak("Hello WPF.");

SpeechSynthesizer Properties

The SpeechSynthesizer has four the properties - Rate, State, Voice, and Volume to get and set the rate, state, voice, and volume of the speech. The value of rate is between -10 to 10 and the value of Volume is between 0 and 100. The Voice is the VoiceInfo object and State is SynthesizerState object. I will discuss these properties in more details in my forthcoming articles.

Asynchronous Speech

The SpeakAsync method speaks asynchronously and takes a Prompt, PromptBuilder or string as input text.

SpeechSynthesizer ss = new SpeechSynthesizer();

ss.SpeakAsync("Hello WPF");

The Application

Based on the above class, properties, and methods, I built an application that allows you to browse a text file, open it in a RichTextBox control, set the volume and rate of the speech and it speaks it for you.

The application UI looks like Figure 4.

Figure 4.

The XAML code for controls looks like following:

<Button Height="23" HorizontalAlignment="Right" Margin="0,0,12,8"

Name="TalkButton" VerticalAlignment="Bottom" Width="101" Click="TalkButton_Click">

Speak

</Button>

<RichTextBox Margin="0,45,0,67" Name="richTextBox1" Background="#FF302F2F"

Foreground="White" />

<Button Height="23" HorizontalAlignment="Left" Margin="318,10,0,0"

Name="OpenTextFileButton" VerticalAlignment="Top" Width="110" Click="OpenTextFileButton_Click">

Open a Text File

</Button>

<Button Height="23" HorizontalAlignment="Right" Margin="0,10,12,0" Name="OpenWavFileButton"

VerticalAlignment="Top" Width="110" Click="OpenWavFileButton_Click">

Open a Wav File

</Button>

<TextBox Height="23" Margin="10,10,0,0" Name="FileNameTextBox" VerticalAlignment="Top"

HorizontalAlignment="Left" Width="299" />

<ComboBox Height="23" HorizontalAlignment="Left" Margin="90,0,0,30"

Name="VolumeList" VerticalAlignment="Bottom" Width="120" SelectedIndex="4" >

</ComboBox>

<Label Height="28" HorizontalAlignment="Left" Margin="0,0,0,25"

Name="label1" VerticalAlignment="Bottom" Width="83">Volume:</Label>

<ComboBox Height="23" HorizontalAlignment="Right" Margin="0,0,130,30"

Name="RateList" VerticalAlignment="Bottom" Width="120"

SelectedIndex="2">

</ComboBox>

Rate:</Label>

In this application, the Open a Text File button opens a file browser and you can open a text file. After that it reads the text file and opens it in the RichTextBox control. The code listing is shown below on the Open a Text File button click event handler.

private void OpenTextFileButton_Click(object sender, RoutedEventArgs e)

{

OpenFileDialog dlg = new OpenFileDialog();

dlg.InitialDirectory = "c:\\";

dlg.Filter = "Text files (*.txt)|*.txt|All Files (*.*)|*.*";

dlg.RestoreDirectory = true;

if (dlg.ShowDialog() == System.Windows.Forms.DialogResult.OK)

{

LoadTextDocument(dlg.FileName);

FileNameTextBox.Text = dlg.FileName;

}

private void LoadTextDocument(string fileName)

{

TextRange range;

System.IO.FileStream fStream;

if (System.IO.File.Exists(fileName)) {

range = new TextRange(richTextBox1.Document.ContentStart, richTextBox1.Document.ContentEnd);

fStream = new System.IO.FileStream(fileName, System.IO.FileMode.OpenOrCreate);

range.Load(fStream, System.Windows.DataFormats.Text);

fStream.Close();

}

The Speak button click event handler sets the volume and rate of the speech after getting these values from the Volume and Rate ComboBoxes and sets the Rate and Volume property of SpeechSynthesizer and after that calls the Speak method.

The following ConvertRichTextBoxContentsToString method reads the contents of the RichTextBox and converts to a string.

Here is the Speak button click event handler:

private void TalkButton_Click(object sender, RoutedEventArgs e)

{

ComboBoxItem volumeItem = (ComboBoxItem)VolumeList.Items[VolumeList.SelectedIndex];

Int32 vol = Convert.ToInt32(volumeItem.Content.ToString());

ComboBoxItem rateItem = (ComboBoxItem)RateList.Items[RateList.SelectedIndex];

Int32 rate = Convert.ToInt32(rateItem.Content.ToString());

talker.Volume = vol;

talker.Rate = rate;

talker.Speak(ConvertRichTextBoxContentsToString());

}

string ConvertRichTextBoxContentsToString()

{

TextRange textRange = new TextRange(richTextBox1.Document.ContentStart,

richTextBox1.Document.ContentEnd);

return textRange.Text;

}

Summary

The Speech API (SAPI) 5.3 is a managed API that comes with Windows Vista. In this article, I discussed how to use the SAPI in a WPF application to build speech-enabled applications. This article covered the text-to-speech (TTS) or Speech Synthesis where we built an application that converts text to speech.

In my next articles in this series, I will add more features to this application including word highligting and spell check. In the next part of this series, I will cover speech recognition in SAPI and WPF.

I hope you enjoyed this article. All feedback and criticisms are most welcome. Feel free to post them at the bottom of this article.