FIR Filter Design using windowed ideal filter method.
| Parameters: | N – order of filter (number of taps) : cutoff – cutoff frequency of filter (normalized so that 1 corresponds to : 
 width – if width is not None, then assume it is the approximate width of : 
 window – desired window to use. :  | 
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| Returns: | h – coefficients of length N fir filter. :  |