# inverse DTFT ideal frequency response of low pass filter

Thread Starter

#### nothing909

Joined Nov 5, 2016
54
can someone explain why the ideal frequency response of a low pass filter cant be implemented using the inverse discrete time fourier transform.

i understand the concept of why it cant be implemented because a digital filter is infinite and non-causal, but i can't explain it using the equation. can someone help?

looking at this equation for an ideal low pass filter:  DTFT          sinc

how can i explain using this that the ideal frequency response cannot be implemented in practise?

#### simozz

Joined Jul 23, 2017
119
The transition band of the frequency response depends on the order of the filter.

To obtain an infinitely narrow transition band like the brick wall frequency response, how many coefficients would you need ?

Thread Starter

#### nothing909

Joined Nov 5, 2016
54
The transition band of the frequency response depends on the order of the filter.

To obtain an infinitely narrow transition band like the brick wall frequency response, how many coefficients would you need ?
An infinite amount of coefficients?