TWO STEP FAST FOURIER TRANSFORM METHOD

摘要

PURPOSE:To allow application of a window function, having ripple characteristics in a predetermined pass band and a side lobe level in a folding region, to two step FFT by increasing the degree of freedom in the design of the window function for rough FFT(Fast Fourier Transform method). CONSTITUTION:A window multiplier sets the order of a window function U times as high as the order N of rough FFT and conducts multiplication of a window function having length U.N for an input sample data overlapped at the overlap rate for the order N of rough FFT. An adder 12 divides the multiplication results into U blocks and conducts addition of samples between the blocks thus determining N sample data which are then inputted to a frequency analyzer 4 for rough FFT thus executing N order rough FFT.