title: change in value of one frequency bin affect FFT and IFFT values of non changing bins
body: <p>I have a 3001x577 matrix. I want to apply a operation to the first 120 samples. I have applied to the first 120 samples which accounts to 20 Hz of frequency. The sampling rate is 2 msec. So I have Fnyq =250hz. Now I have taken out the first 120 samples. I noticed that after applying the filter and replacing it with the older 120 samples, the values of bins greater than 120 has changed after I applied an IFFT . And this is evident on my final result. I got the desired filter result but it ends up changing values of samples which i want untouched.</p>
  
  <p>Can someone explain why change in value of few frequency bins affect the ifft or fft of non changing bins. I am using matlab. And how can i prevent it?</p>