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What's better for DSP: IIR or FIR filters?

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amiran2001

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IIR filters are better for dsp or FIR filters?
 

Re: IIR or FIR

FIR filters are easy to implement and stable,but they need higher order.IIR filters are difficult o implement but need lower order.
 

Re: IIR or FIR

First of all the use depends upon the appliation of the problem. If you want linear phase and stable output, you have to go for FIR. IIR's are always not linear but can be designed to be stable.
 

Re: IIR or FIR

i think
fir filters are more effecient thatn IIR, mostly FIR filters are used because they are stable.
 

Re: IIR or FIR

Another criteria to chose between a FIR ofr IIR implementation is the need for phase linearity to avoid distortions in the output signal: FIR filters have linear phase response, at the expense of greater HW/SW resource occupation.

Bye
Mowgli
 

IIR or FIR

who can tell me, why we deed to design FIR or IIR?
why not FFT the signal first, and then remove the signal out the frequency band, then IFFT the signal, this process complete the signal filter, it is also fast and available?
why not??????????
 

IIR or FIR

Virttually all DSP applications, have some form of FIR or IIR filters.

Actually, the design of the filter comes after you analyze the signal before hand. Thats why your process is

1.) Gather the signal characteristics. You need to perform FFT here to know the frequenccy components in your signal.

2.) Design a filter. Since you know what are the frequency contents in your signal you can suppress or remove those unwanted components in your signal. This comes the design of FIR or IIR filters.

3.) Convolve or apply your signal to your filter, you get hopefully your desired signal components.


Normally in DSP products, few implement FFT and IFFT algorithms on chip, because these algorithms are rather computationaly extensive and eat lots of system resources. So they analyze the signal first, and design appropriate filters.


Which is better IIR or FIR

IIR filters:
1.) From the name alone, Infinite Impulse Response, means a lot of computation is required which translates into huge resources intake. RAM, program space and computing time.

2.) Becauae IIR filters have poles in their trasfer functions, there is a tendency that the filter becomes unstable; literraly you can get a huge magnitude response or during computaion you get overflow in the resulting computations. Poles can lead to divide by zero which can make the filter unstable.

3.) Some IIR filters hovever can be converted to FIR to improve stability. The Digital FIR Chebyshev filters for example.

FIR filters:
1.) Filter coefficients are finite; however, number of filter coefficient should be sufficiently large so that the computations will converge close to the actual response.

2.) Always stable. FIR filters have no poles in the transfer function.


Hope this clears a bit.
 

Re: IIR or FIR

lmjandy said:
who can tell me, why we deed to design FIR or IIR?
why not FFT the signal first, and then remove the signal out the frequency band, then IFFT the signal, this process complete the signal filter, it is also fast and available?
why not??????????

Did you count the cost of FFT?

Added after 1 minutes:

noviceca said:
lmjandy said:
who can tell me, why we deed to design FIR or IIR?
why not FFT the signal first, and then remove the signal out the frequency band, then IFFT the signal, this process complete the signal filter, it is also fast and available?
why not??????????

Did you count the cost of FFT?

FFT is a kind of block processing, but filter implemented at the time domain is not but pipelined.
 

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