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Sphinx is a speaker-independent large vocabulary continuous speech recognizer. It is also a collection of free and open source tools and resources that allows researchers and developers to build speech recognition systems. The packages that the CMU Sphinx Group is releasing are a set of reasonably mature, world-class speech components that provide a basic level of technology to anyone interested in creating speech-using applications without the once-prohibitive initial investment cost in research and development; the same components are open to peer review by all researchers in the field, and are used for linguistic research as well. Sphinx-3 is CMU's state-of-the-art large vocabulary speech recognition system. It uses Hidden Markov Models (HMM) with continuous output probability density functions (PDF). It supports several modes of operation. The more accurate mode, known as the "flat decoder", is descended from the original Sphinx-3 release (still available for reference purposes at The faster mode, known as the "tree decoder", was developed separately. The two decoders were merged in Sphinx 3.5, though the flat decoder was not fully functional until Sphinx 3.7. Further documentation can be found in the release documentation, or at the online documentation.

Documentation and


Download version 0.8 (beta)
released on 17 February 2009


Related Projects


LicenseVerified byVerified onNotes
X11Kelly Hopkins17 February 2009
BSD 2ClauseKelly Hopkins17 February 2009

Leaders and contributors

Evandro Gouvêa Maintainer
Mosur Ravishankar Maintainer
Arthur Chan Maintainer

Resources and communication

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Developer Homepage
Bug Tracking Bug Tracking
General Forum
Support Forum
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Software prerequisites

This entry (in part or in whole) was last reviewed on 17 February 2009.


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