Exactly why using the of windowing function, such as Hamming or Blackman, causes a slower transition to stop band? Everywhere it is mentioned just as an obvious fact that this happens but I haven't found a text that mentions what is the cause.
An example for what I mean:
- An FIR low-pass filter designed with cut off frequency 1 Hz without a window function reaches stop band at little over this frequency (1.04 Hz or so).
- When window function is applied, the filter reaches the stop band at over 1.2 Hz
Also, is there a way to compensate for this? For example, if I really want the cut off frequency to be 1 Hz and use window function, should I design the filter to have cut off say 0.9 Hz?