1.   All we can say in general is that there is a critical frequency, a knife-edge.

2.   They also adversely affect the rate at which the attenuation changes with frequency near critical frequencies.

3.   Making the characteristic impedances of the constant-k and m-derived filter sections identical also ensures that their critical frequencies are the same.

4.   Checking this point, the critical frequencies of m-derived T and -sections are determined by, that is, by and respectively.

5.   It is easily seen that these conditions are identical and reduce to just, the condition governing the critical frequencies of the constant-k prototype.

6.   Making m small sets the resonant frequency very close to the critical frequency so that the attenuation of the prototype is enhanced where it is weakest.