frequency response to phase and magnitude representation
[db,phi] =dbphi(repf)
:db,phi vector of gains (db) and phases (degrees) : :repf vector of complex frequency response :
db(k) is the magnitude of repf(k) expressed in dB i.e. db(k)=20*log(abs(repf(k)))/log(10) and phi(k) is the phase of repf(k) expressed in degrees.