There are TWO high-pass filters in that circuit.
The input cap is one.
The emitter-resistor-bypass is the other.
Both of these capacitors cause a rising output signal level.
Thus 12 db/octave or 40dB/decade.
Its your job to manage the timeconstants of these TWO HPF.
What is the input impedance?
Zin is Z(c1) + the parallel combination of
a) R1
b) R2
c) Miller Capacitance [stage voltage gain * Cob (C collecter to base) ]
d) the sum of beta1/gm + { R4 in parallel with Z(20uF) }, where beta1/gm is R_pi.