Google-Cloud-Speech-to-Text-API and Google-Speech-to-Text-API comparison
Speech recognition is an interdisciplinary subfield of computational linguistics that develops methodologies and technologies that enables the recognition and translation of spoken language into text by computers. It is also known as automatic speech recognition, computer speech recognition or speech to text.
The OSR Project provides freely usable speech files in multiple languages for use in Voice over IP testing and other applications.
http://www.voiptroubleshooter.com/open_speech/index.html
http://www.voiptroubleshooter.com/open_speech/american.html