# Butterworth function vs. Bessel function

Started by April 26, 2010
Hi,

I am a logic designer new to the DSP area and I have a few basic questions regarding FIR/IIR filters. Any help/pointers is appreciated.

I read that FIR filters have no poles , it has only zeroes. In that case, how can I design a 4-pole FIR filter?
Does 4-pole, 4-tap, and 4th order filters all mean the same thing?
I used an online tool to come up with the coeffiencts for a 4-pole filter. I chose butterwort and bessel. In both cases, the forward coeffiecients were the same, only the feedback coeffiecients were different. In that case, if the filters are FIR (which has no feedback), what is the difference in the implementation of a Butterworth function vs. Bessel function?

thanks
Aarathi
You don't understand basics so I'd suggest You to find a good textbook on digital filter design. This is just an example of one of free sources of info on the subject: http://www.analog.com/static/imported-files/seminars_webcasts/MixedSignal_Sect6.pdf. It is not the best possible source but it is quite simple for the beginner and covers the main aspects of digital filtering.

As for Butterworth and Bessel filters, they are both IIR filters. They are the digital equivalents of the corresponding analog filters, which have similar transfer functions but different frequency and transient response characteristics. You can find more on this subject from the above mentioned link and also here http://www.analog.com/library/analogDialogue/archives/39-05/Web_Ch5_final_PtA.pdf.

--
Alexander

Hi,
>
>I am a logic designer new to the DSP area and I have a few basic questions regarding FIR/IIR filters. Any help/pointers is appreciated.
>
>I read that FIR filters have no poles , it has only zeroes. In that case, how can I design a 4-pole FIR filter?
>Does 4-pole, 4-tap, and 4th order filters all mean the same thing?
>I used an online tool to come up with the coeffiencts for a 4-pole filter. I chose butterwort and bessel. In both cases, the forward coeffiecients were the same, only the feedback coeffiecients were different. In that case, if the filters are FIR (which has no feedback), what is the difference in the implementation of a Butterworth function vs. Bessel function?
>
>thanks
>Aarathi
>