Butterworth 's filter implementation is , in those terms , an insertion - loss filter .
Insertion - loss filter is a relatively trivial one mathematically since the active amplifiers used by Butterworth ensured that each stage individually worked into a resistive load .
Butterworth 's filter implementation is , in those terms , an insertion - loss filter , but it is a relatively trivial one mathematically since the active amplifiers used by Butterworth ensured that each stage individually worked into a resistive load .