how to get the biquad filter as eq?

[ChR_is]

Just to chip-in here...

Biquad filters have known side-effects - if you modulate the cutoff frequency they can "blow-up" (edit: basically a divide by zero).

For set frequencies, they work fine but tweaking the cutoff in realtime with a knob on the UI is asking for trouble

Cheers, -Rob @ WI

That is very much true. the biquad filter should not be modulated quickly. it can withstand some slow modulation like smoothed knob tweaks, but that's also asking for trouble. to get around this issue you can smooth the change in cutoff frequency or interpolate the change in coefficients over time. both methods produce slightly different results, but work just fine.
an even better approach would be to not use biquad filters. instead use trapezoidal state variable filters. these can be modelled to essentially behave the same without any of the issues. Cytomic has published a nice paper detailing the process with pseudo code included as well: cytomic svf paper
these filters are efficient and can be modulated at audio-rate.