Difference between IIR and FIR filters

The field of digital signal processing or DSP includes the design and implementation of filters to filter the signals. These filters are mainly classified into two types depending on the duration of their impulse responses. They are known as infinite impulse response (IIR) filters and finite impulse response (FIR) filters. Let’s see the actual difference between IIR and FIR filters.

Difference between IIR and FIR filters in tabular form

IIR Filter FIR Filter
IIR filter stands for infinite impulse response filter. FIR filter stands for finite impulse response filter.
An IIR filter gives impulse responses for an infinite duration of time. A FIR filter provides impulse responses for a finite duration of time.
Feedback system is available in IIR filters. Feedback system is not present in FIR filters.
The IIR filter is recursive. The FIR filter is non-recursive in nature.
IIR filters are less stable than that of FIR filters due to the presence of poles. FIR filters do not contain any poles. Hence the FIR filter is always stable and the stability is more than that of IIR filter.
The transfer function of IIR filter contains both poles and zeros. The transfer function of FIR filter contains only zeros.
The memory requirements of an IIR filter is less than that of FIR filter as it contains feedback path. Due to the absence of feedback path in the FIR filters, it needs more memory to keep the more number of coefficients even for a single function.
The computational efficiency of an IIR filter is more than that of a FIR filter. The computational efficiency of a FIR filter is less.
Butterworth filter, Chebyshev type I filter, Chebyshev type II filter, etc. Differentiator, Hilbert transformer, etc.
In biomedical sensor, telecommunication, audio equalization, the IIR filters are used. The uses of FIR Filters are found in audio system, control system, medical devices, etc.

What is IIR Filter?

The IIR filters represent the digital filters that generate infinite impulse response of a dynamic system. The transfer function of the IIR filter contains both the poles and zeros in it. In order to make the filter stable, the poles of the filter must lie inside a unit circle. The sensitivity of the IIR filter is more, hence not easy to control.

What is FIR Filter?

The FIR filters represent the digital filters that generate finite impulse response of a dynamic system. In the transfer function of FIR filters, only zeros are present, making the filter more stable. The generation of current output requires the past and present samples of the input. The FIR filter has a comparatively low sensitivity that makes the filter more controllable.


The IIR filter and the FIR filters are a very important part of digital signal processing. According to the modes of operation and output needed, the filters can be used easily. These digital filters are designed in various computer software programs. The filters work with the frequency transformation of the system in both the analog and digital domains.


Sunmoni Gohain
NIT Silchar

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