Using Microsoft TTS for commercial use

License to use Microsoft Speech for TTS and Speech Recognition is included with your Windows OS license.
commercial licensing would be required for any type of commercial use or ability to distribute the audio files.

You need to buy license, When you buy a Windows (or Office) license you are granted the right to use it to generate outputs of various types. What you can't do is resell the basic tools. Without license you can’t use Microsoft's TTS voices for commercial use

Microsoft has copyright on its application used in Windows Operating System. However, you may refer to the following article for more information on Microsoft Copyrights and there’s also contact detail and you can write them as well regarding your doubts on Microsoft Copyrights.
Use of Microsoft Copyrighted Content
http://www.microsoft.com/en-us/legal/intellectualproperty/Permissions/default.aspx

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