faq

隐马尔科夫模型工具箱

			HTK3 FAQ

License Issues
==============

What is the role of Microsoft in all this?

        See the 'History of HTK' page on the website for a full
        explanation. The short version is:

        HTK was originally developed at the Cambridge University
        Engineering Department (CUED). 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.
        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.


Can I build & sell products based on HTK3?

        You may build a product but you are not allowed to
        redistribute (parts of) HTK3, i.e. you can't ship shrink-wrap
        boxes with products that contain HTK3 code.

Can I use this version for teaching & academic research?

        Yes, absolutely.

Can I use this version in commercial product Research & Development?

        Yes. You can for example use HTK3 to train models that are
        then used in your products.


General
=======

What is HTK and what is it not?

        HTK is a toolkit for research in automatic speech recognition
        and has been used in many commercial and academic research
        groups for many years.

        It is not a desktop dictation system or an application that
        you just install on your PC to get a speech interface to your
        computer.

Are there any teaching materials available that use HTK3?

        Not yet, but we always welcome contributions.

I have a problem using HTK3 -- where can I get support?

        A set of mailing lists have been created to help solve HTK
        related problems (see Mailing List page). Queries about the use
        of HTK3 should be addressed to [e-mail].


Source Code
===========

What is the difference between this version and the Entropic one?

        The HTK3 code is based on the final release from Entropic
        (V2.2_ref). The source code now contains Microsoft Copyright
        headers; there is revised and consistent indentation and some
        minor changes to remove some compiler warnings have been made.
        Functionally the code in HTK 3.0.0 should be identical to HTK
        V2.2_ref.


Can I build the CU-HTK Hub4/5 evaluation system with HTK3?

	No. The HTK version used internally at the Cambridge
	University Engineering Department has some extra
	functionality not available in HTK3; such as PLP
	coefficients; vocal tract length normalisation; extended 
        types of adaptation; lattice operations; support for
        context dependency beyond triphones; long-span language model
        support etc. Some of the most generally useful of these
        features will be made available in HTK3 over the next few months.
        In addition to this HTK3 does not include a large vocabulary
        decoder that is usable with cross-word triphones and 
        long-span language models at the moment (HVite can rescore
        but not generated lattices for such configurations). 
        We hope to be able to provide a capable large vocabulary decoder
        in the medium term.

What kind of computer/OS do I need to run HTK3?

         The distributed version of HTK3 should build on Solaris,
         IRIX, HPUX and Linux. If it doesn't, please file a bug
         report. HTK has also been successfully built on Windows NT.


Commonly used abbreviations:

   CUED - Cambridge University Engineering Department
   HTK - Hidden Markov Model Toolkit
   PLP - Perceptual Linear Prediction