Since the default Resonance is 1 / sqrt (2) and not 1 I wonder how to calculate from db boost/cut at res frequency to the value you enter in setResonance.
Resonance in this case means Q factor, which is the amplitude response at the cutoff. dB is
20*log10 of anything -for example
20*log10(amplitude) is often called level. So if you have your cutoff level in dB, your resonance (Q) is
10^(dB/20). Notice that for high Q this is not the actual max amplitude -the peak of resonant filters is a little behind the cutoff point: