What is HTK?

The Hidden Markov Model Toolkit (HTK) is a portable toolkit for building and manipulating hidden Markov models. HTK is primarily used for speech recognition research although it has been used for numerous other applications including research into speech synthesis, character recognition and DNA sequencing. HTK is in use at hundreds of sites worldwide.

HTK consists of a set of library modules and tools available in C source form. The tools provide sophisticated facilities for speech analysis, HMM training, testing and results analysis. The software supports HMMs using both continuous density mixture Gaussians and discrete distributions and can be used to build complex HMM systems. The HTK release contains extensive documentation and examples.

HTK was originally developed at the Speech Vision and Robotics Group of the Cambridge University Engineering Department (CUED) where it has been used to build CUED's large vocabulary speech recognition systems (see CUED HTK LVR). In 1993 Entropic Research Laboratory Inc. acquired the rights to sell HTK and the development of HTK was fully transferred to Entropic in 1995 when the Entropic Cambridge Research Laboratory Ltd was established. HTK was sold by Entropic until 1999 when Microsoft bought Entropic. Microsoft has now licensed HTK back to CUED and is providing support so that CUED can redistribute HTK and provide development support via the HTK3 web site. See History of HTK for more details.

While Microsoft retains the copyright to the existing HTK code, everybody is encouraged to make changes to the source code and contribute them for inclusion in HTK3.

Join the HTK Team at CUED

If you are interested in joining the HTK Team and work on software development or algorithm research (either as an RA or PhD student) send email with your CV to Phil Woodland <pcw@eng.cam.ac.uk>

Current releases

At the moment, the only release version of HTK is version 3.0.

Getting HTK

HTK is available for free download but you must first agree to this license. You must then register at CUED for a username and password for downloading HTK from the server in Cambridge.

HTK News

17 May 2001 (ge):

• The meeting of HTK users at ICASSP'01 was a big success. The slides for Gunnar's talk are available here.

20 Apr 2001 (ge):

• A meeting of HTK users will be held on May 10th in Salt Lake City

18 Apr 2001 (ge):

• First beta version of HTK 3.1 available

27 Sep 2000 (rjw):

• HTK3 web-site launched.