It is best to consider two situations. If the interference of the input signal is relatively large, filter first, extract useful components as much as possible, and attenuate useless high-frequency interference. At this point, if you amplify first, the high-frequency interference will be amplified, and then filtering will not be easy to attenuate. Although theoretically, whoever comes first will have the same effect. If the input interference is small, it can be amplified first and then filtered. Because the interference is small, the filtering is not obvious. So enlarge it first and then filter it out!