First of all, thanks Dmitri for replying to my previous query.
I am now facing some problems in filtering the signal. I tried using an band-pass elliptical filter using the command "[N, wn] = ellipord (wp,ws,rp,rs)". But the command screen shows the message that the "ellipord undefined near line xx column yy". I have the same problem when using a Butterworth filter i.e "[N, wn] = buttord (wp,ws,rp,rs)" Is this because I dont have the required function installed or is it somthing else? I am currently using GNU Octave 2.1.36 version. Are these functions available in the latest version? Please reply asap.