Audio and video support is a core pillar of the WPF platform. However, WPF also includes libraries that wrap two less commonly used multimedia features: speech synthesis and speech recognition.
Both of these features are supported through classes in the System.Speech.dll assembly. By default, Visual Studio doesn't add a reference to this assembly in a new WPF project, so it's up to you to add one to your project.
Speech is a peripheral part of WPF. Although the speech support is technically considered to be part of WPF and it was released with WPF in the .NET Framework 3.0, the speech namespaces start with System.Speech, not System.Windows.
Speech synthesis is a feature that generates spoken audio based on text ...