The two T-notch filter
can be used to block unwanted frequencies or if placed in an op amp as a
bandpass filter. the notch frequency occurs where the capacitive
reactance equals the resistance (Xc = R) and if the values are close,
the attenuation can be very high and the notch frequency virtually
eliminated,Insertion of the filter depends on the load, the output is
connected to the subject so that the resistors must be of much lower
value than the load for minimal loss.
For audio frequencies, the filter may act as a bass and treble boost
circuit by attenuating the midrange. With 1.5K resistors and capacitors
0.1 uF, the band is in stop-10dB 500 Hz to 2 kHz. The depth and breadth
of the reaction can be slightly adjusted to a value of 0.5 R and adding
some resistance at the C-values,If the circuit is an operational
amplifier is used as a bandpass filter, the response should be reduced
to avoid oscillation.