## What is a realizable filter?

A filter is realizable iff its impulse response is stable and causal. Ideal filters are not realizable (not causal)

### Why is ideal filter not realizable?

All ideal filters are non-causal systems. Hence none of them is physically realizable. <∞ A system whose magnitude function violets the paley-wiener creation has non-causal impulse response, the response exists prior to the application of the driving function. That means ideal filters are not physically realizable.

**Why an ideal low-pass filter is not physically realizable?**

The inverse Fourier transform of will consist of function since the frequency domain has function. From Figure 2, The ideal low pass filter is non-causal. Therefore, the ideal low-pass filter is non-causal and hence physically not realizable.

**What are non ideal filters?**

A non-ideal low-pass filter passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cut-off frequencies.

## What is ideal filter?

An ideal filter is considered to have a specified, nonzero magnitude for one or more bands of frequencies and is considered to have zero magnitude for one or more bands of frequencies. On the other hand, practical implementation constraints require that a filter be causal.

### What is drawback of ideal filter?

Inputs can be delayed for the implementation of a discrete time system that only uses input samples (FIR filter, for example). The delay itself leads to a phase change which is inconsistent with the frequency response specification for an ideal filter.

**What is the difference between ideal filter and practical filter?**

**Why are ideal filters cannot be realised practically?**

Another point of view into their unrealizability is that input/output relationship of such ideal filters cannot be described by finite order differential / difference equations.

## Is the magnitude of an ideal filter zero?

The magnitude function 𝐻𝜔) may be zero at some discrete frequencies, but it cannot be zero over a finite band of frequencies since this will cause the integral in the equation of paley-wiener creation to become infinite. That means ideal filters are not physically realizable.

### When to use the ideal low pass filter?

Now consider the intermingled sinc function [i.e., (sin X )/ X] impulse responses of the ideal lowpass filter when it is subjected to a sequence of uniformly spaced delta-function impulse voltages of random polarity, as sketched in Fig. 17.8.

**Why do we need a zero group filter?**

Note that while the above considerations have tacitly assumed zero group delay through the filter for ease of illustration, the inclusion of a linear group delay term τ would merely cause each of the sinc function impulse responses to experience the same delay, allowing the maintenance of ISI-free transmission under ideal conditions. 2.1.