Difference Between FIR Filter and IRR Filter

Digital Signal Processing applications make heavy use of filters, and two of the most popular ones are FIR filter and IRR filter. There are many who remain confused about the usability of one or the other in different circumstances as though there are many similarities in the two types, there are glaring differences also. This article will highlight the differences between FIR and IRR filters to enable users to make better use of these filters in digital signal processing.

What is FIR Filter?

FIR stands for Finite Impulse Response. It means that if an impulse has been put, for example a 1 followed by many zero samples; zeroes will always come out after 1 has passed through the delay line of the filter. The reason this filter is called finite is because of a lack of feedback. No feedback ensures that impulse response will be finite. This is precisely why FIR is also called no feedback filter. However, even when feedback is employed, the response is finite in the case of FIR filters.

What is IRR Filter?

The alternative to FIR filters is IIR or Infinite Impulse Response filters. The output rings indefinitely when an impulse is input in case of IIR filter.

Advantages of  FIR Filter

Both FIR and IIR filters have their own features and pros and cons. In general, the advantages of FIR are far more than its disadvantages which mean they are used more widely than IIR filters. Following is a summary of the advantages of FIR filters.

– It is easier to design FIR filters to be in a liner phase. This design delays the input signal without distorting its phase.

– FIR filters are easy to install and FIR calculation in all DSP microprocessors can be completed using single looping function.

– Whether you are reducing the sample rate (decimating), or increasing the sample rate (interpolating), the use of FIR filters allows for omission of some calculations thus improving efficiency.

– FIR filters can be installed with simple fractional mathematics making implementations simple.

However, in comparison to IIR filters, FIR filters use more memory and calculation to achieve a response characteristic of a filter. In addition, there are some responses for which FIR filters are not suitable.

What is the difference between FIR Filter and IRR Filter?

• Both FIR and IIR are utilized for filtration in digital processing.

• IIR filters are dependent upon both input and output whereas FIR filters depend only upon input.

• IIR filters are unstable whereas FIR filters are stable

• IIR filters require more memory than FIR filters

• IIR filters are difficult to implement in comparison to FIR filters

• While IIR can easily simulate analog signals, FIR does not have the capacity for it

• FIR filters are of a higher order than IIR filters

• Where linear characteristics are not important, IIR filters are preferred