> how to find about voice filtering methods

Google for them? Wiener filter for example or Ephraim filter

See also

http://www.voxforge.org/home/docs/speech-recognition-book

> how to use them to speech recognition using HTK or sphinx

Open source code, implement the filter, use it

See also

http://oreilly.com/catalog/9780976694045

hope it will be useful for you.

--- (Edited on 11/10/2009 19:40 [GMT+0300] by nsh) ---