当系统规格需要具有陡峭的频率截止特性的低通滤波器时,工程师可以选择具有锐过渡频带的“砖墙式”滤波器设计。例如,在调频立体声广播系统中,基带音频的左右声道中的低通滤波器应该具有至少15kHz的-3dB截止频率和低于0.3dB的通带纹波,以及至少19kHz的阻带起始频率、大于50dB的阻带衰减和对两个声道完全相同的相位响应。 When system specifications require a low-pass filter with steep frequency cut-off, engineers can choose a “brickwall” filter design with sharp transition bands. For example, in FM stereo broadcasting systems, the low-pass filters in the left and right channels of baseband audio should have a -3 dB cutoff frequency of at least 15 kHz and a passband ripple below 0.3 dB and a stopband start frequency of at least 19 kHz Stopband attenuation greater than 50 dB, and exactly the same phase response to both channels.