Is it possible to get a wider Q shape?

[WillowWolf]

Hello everyone! I've been lurking on the forum for a while, and finally have something to post about!

I'm currently making an SSL style EQ plugin, and I'm curious if it's possible to get a wider bell curve Q shape than what's available by default from either the parametric EQ effect, or from the svf_eq. Right now the 0.3 Q setting is still much narrower than the Q shape on the SSL consoles I've tested.

I'm currently exploring wonky solutions to this problem like using parallel bandpass filters. Any advice would be super helpful!

[Dan Korneff]

As you've noticed, the SSL RC networks are reactive (interacts with the gain) and a low gain boost is much wider than the RBJ cookbook formulas in the biquad/svf.
The best solution is to create a state space model so you not only get the curves, but also the proper phase shift and nonlinearities that come with the analog design.
If you're just going to match the curves with the existing designs, you'll probably have to stack multiple filters at different frequencies to mimic the wider Q.

[griffinboy]

@Dan-Korneff
@WillowWolf

Indeed.
Creating a custom filter is your best bet.

Digital SVFs are a particular topology which have limits to the shapes you can make with them. There are a few different methods to choose from to create digital filters with more flexible frequency responses.