recording real sound data from microphone into matlab

   Ns=2^17;

   Fs=44100;%in Hz              

   y=wavrecord(Ns,Fs,1,'double');

filename ='cdct.wav';

   wavwrite(y,Fs,filename);

   n=length(y);

   t=(0:(n-1))*Ns/n;

plot(y)

   xlabel('time in(sec)')

   ylabel('amplitude')

   titel('amp vs time')

    my questions are:

        1. I used this code to record the sound data ,but  I fail to determine 

              its fundamental frequency

          2.how can add a code for filtering during recording

             any help!10Q