Which statement is not an accurate description of differences between FIR and II
ID: 1715892 • Letter: W
Question
Which statement is not an accurate description of differences between FIR and IIR filters?
a. Recursive filters have poles determined by the denominator polynomial, which means that they cannot guaranteed to be stable, a factor that was not a concern with FIR filters.
b. IIR filters are difficult to design to provide linear phase in the pass band of the filter, unlike FIR filters where linear phase was a guarantee.
c. IIR filters require fewer coefficients than FIR filters for similar filter design requirements and thus, require less memory and execute in less time.
d. IIR filters are capable of smaller transition widths between pass bands and stop bands and also may provide greater attenuation in the stop bands than FIR filters.
Explanation / Answer
Option B is not accurate
The reason is :
The main advantage digital IIR filters have over FIR filters is their efficiency in implementation, in order to meet a specification in terms of passband, stopband, ripple, and/or roll-off. Such a set of specifications can be accomplished with a lower order (Q in the above formulae) IIR filter than would be required for an FIR filter meeting the same requirements. If implemented in a signal processor, this implies a correspondingly fewer number of calculations per time step; the computational savings is often of a rather large factor.
On the other hand, FIR filters can be easier to design, for instance, to match a particular frequency response requirement. This is particularly true when the requirement is not one of the usual cases (high-pass, low-pass, notch, etc.) which have been studied and optimized for analog filters. Also FIR filters can be easily made to be linear phase (constant group delay vs frequency)—a property that is not easily met using IIR filters and then only as an approximation (for instance with the Bessel filter). Another issue regarding digital IIR filters is the potential for limit cycle behavior when idle, due to the feedback system in conjunction with quantization.
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