# How would one design a (quasi) linear phase adaptive notch filter for a single complex tone?

While IIR notch filters are attractive, I need to retain phase linearity at the filter output. I imagine that it's possible to use a standard IIR notch filter: https://www.researchgate.net/publication/224174145_A_Complex_Adaptive_Notch_Filter followed by some form of phase equalization. An alternative would be an FIR filter with conjugate symmetric coefficients. I am unaware of any FIR designs in the literature explicitly for a single complex tone.

Any thoughts on the best way forward?

• Question what's the phase of a standard IIR notch filter when you're not close to the notch frequency? Answer : Almost 0, hence almost linear. I suspect that a standard IIR notch filter is good enough
– Ben
Jan 30 '20 at 1:26
– Ben
Jan 30 '20 at 2:10