# Do we guess the cut off frequency when passband edge frequency and stop band edge frequency are given? FIR Filter design-LOW PASS FILTER

Say passband edge frequency=0.25 $$\pi$$

Stopband edge frequency=0.35 $$\pi$$

What is the cut off frequency? Do we average these 2 frequencies and write the answer or what is the procedure to find cut off frequency?

This is the question I want to solve-:

Use hamming window method to design a digital low pass filter with pass band edge frequency=0.25$$\pi$$, stopband edge frequency=0.35$$\pi$$ where main lobe width of hanning window is 8*$$\pi$$/M M is filter length.

• If the filter is FIR then it's the arithmetic mean, if it's of an IIR-type then it's the geometric mean. Sep 5, 2021 at 6:02
• First you have to define what you mean by "cut-off frequency". If you don't say "$X$ dB cut-off" for some $X$ (e.g., $3$dB) then the term has no clearly defined meaning. There's no reason why "cut-off frequency" shouldn't be the same as "pass band edge". Sep 5, 2021 at 10:49
• The question is-:Use hamming window method to design a digital low pass filter with pass band edge frequency=0.25pi, stopband edge frequency=0.35pi where main lobe width of hanning window is 8pi/M M is filter length. @MattL. Sep 5, 2021 at 11:23
• Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
– Community Bot
Sep 5, 2021 at 15:46

The graphic below demonstrates this for a rectangular window. For other windows, the transition band will increase for a given number of taps, but the relationship between $$f_c$$ in the desired rectangular frequency response and $$f_c$$ that is midway in the transition band still applies.