matlab中butter和buttap函數的區別

buttap(n) returns the poles and gain of an order n Butterworth analog lowpass filter prototype.

butter designs lowpass, bandpass, highpass, and bandstop digital and analog Butterworth filters.

從這兩條註釋可以看出，butter可以直接設計數字濾波器，而buttap則設計出模擬濾波器，需要設計數字濾波器時，則需要用雙線性變換、脈沖響應不變等方法再轉換。