A more general form of the digitizer transfer function (equation 22) is:
Similarly the frequency response of a geophone can be expressed as:
where q and Q are polynomials in s.
The combined frequency response of a digitizer and a seismometer is the multiple of the two response functions, for the digitizer and for the response of the geophone, i.e.:
where and are the gains of the digitizer and geophone and p, P, q and Q are polynomials. For the RD3/OSD3, p(s) is of first order and P(s) of forth order. For the Lennartz geophones, both q(s) and Q(s) are second order polynomials, where as for the Streckheisen STS-2 q(s) is of order three and Q(s) of order eleven.
The velocity proportional frequency response of the SIL system is shown in Figure 4 for the six types of geophones.
The total gain of the system is the multiple of the filter gain (equation 14), the frequency independent gain of the digitizer (equation 17), and the generation constant of the geophone, , i.e.:
For the Lennartz geophones is 400.0 V/m/s while for Guralp seismometers from the Passcal instrument pool is 2000.0 V/m/s, giving a factor five difference in over all gain.