The high-pass filter
From Atomix
The high-pass filter correction is obtained by multiplying the spectrum by <math>1+\left( \frac{f_c}{f} \right)^2</math> where <math>f_c</math> is the high-pass cut-off frequency and <math>f</math> is the frequency. The high-pass filter is assumed to be of single-pole, or first order, and has a transfer function of <math>\frac{j f/f_c}{1+jf/f_c}</math> where <math>j^2=-1</math>.
