hi first of all sorry for putting it on so late on the net ! the problem which i mentioned in the earlier mail regarding th einaccessibility of the glabal variable placed in another file ... i managed to recover the problem . It was due to the the optimization level in the build option ... i have set it to "level 3 - file" which i changed to none and the code worked fine . i assume that this optimization localazez the compiler to the file only and lost the address of the variabel whicle it is being called in the other file . another question ! any body can tell me that what are the exact methods involved in the spectral analysis ... what i have studied is that 1- take a time limited signal 2-window it 3-take fft of it 4- average out many fft results , to get the average fft in the particular duration . i want to ask that what should be the window used ? and what exactly should be the no. for getting the average of te spectrum for teh elimination of the noise components of unexpected cpomponenets. Thank you Saqib Ali