The Speech API Software Developers Kit (SAPI SDK) contains the documentation, samples, and header and library files to create applications and utilities that use speech recognition and voice synthesis. In addition, the SAPI SDK can be used to create speech recognition and voice synthesis engines that can be used by other applications.

Generally, the version of SAPI is determined by the platform that shipped it. SAPI 5.1 was included with Windows XP along with the Microsoft Sam TTS engine. The initial release of Windows XP did not include a speech recognition engine. The Tablet PC Edition of Windows XP did include version 6.1 of Microsoft's speech recognition engine. This was also shipped with Office 2003. Office 2003 also included SAPI TTS voices from Lernout & Hauspie, called LH Michael and LH Michelle. Also note that some vendors include SR and TTS engines with their products. For example, my laptop came with speech recognition and TTS engine provided by Toshiba.

With Windows Vista, the version of SAPI that is installed is 5.3. We have replaced the Microsoft Sam voice with next generation technology in a new female voice we call Microsoft Anna. We have also made major improvements to the speech recognition engine (now version 8.0) and that is included in all editions of Windows Vista.

For the SDK, you can download the SAPI 5.1 SDK to create applications and engines that work on Windows XP and Windows Server 2003. These applications or engines should also be forward-compatible with SAPI 5.3 on Windows Vista and beyond. The SAPI 5.1 SDK is a stand-alone package, separate from other Microsoft SDK's.

With SAPI 5.3, we integrated our SDK into the main Windows SDK (sometimes known as the Platform SDK). You can use the Windows SDK to create applications for Windows Vista, Windows XP, and Windows Server 2003. What OS version you target is done at compile-time, and that prevents features that only exist in latter versions from being available.

You can get an ISO image to burn the SDK to a DVD here:

To selectively download and install various components of the Windows SDK, go here:

Something else that is new is our Managed Speech API's. Codenamed SpeechFX, the Managed Speech API is part of the Microsoft .NET Framework 3.0. The new System.Speech namespace provides managed classes for speech recognition and synthesis. This makes it much easier to write speech applications from managed code, such as C# or Visual Basic .NET.

The Managed Speech API documentation is included with the Windows SDK. Applications that use .NET Framework 3.0 will work on Windows Vista, Windows XP and Windows Server 2003. Note that you have to redistribute the .NET Framework 3.0 with your application for Windows XP and Windows Server 2003. The framework is already included with Windows Vista.