highpass filter design in Matlab
Transfer function of a 1st order HP filter is:

$$H(s)=\frac s{s+wc}=\frac{{\displaystyle\frac s{wc}}}{1+{\displaystyle\frac s{wc}}}\;,where\;wc=2\mathrm\pi\ast\mathrm{fc}$$

&amp; 

a = [1 w0];
b = [w0 1e-48]; % ! two coefficients