What you said may be true, but it is not a very fruitful way of looking at
the problem. Three reasons I can think of: First, the sampling rate is
usually determined by other factors, such as the nature of the signal, the
analog processing done before the ADC, and the computational power of your
processor. It is not something that you adjust to faciliate the algorithm.
Second, it is easy to made N larger if you want better resolution in your
frequency response specification.
Third, and most im****tant, the frequency resolution of your final filter
does not usually depend on the accuracy of your initial specification. It
depends mainly on the length of the filter kernel.
Here's two links that may help.
Regards,
Steve
http://www.dspguide.com/ch16/1.htm
http://www.dspguide.com/ch17/1.htm
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