Cool, thanks! 
This tool will also be useful as an example of how to draw freqency response in case of a cascaded filter…
The drawing part isn’t that complicated since both dsp::IIR::Coefficient and dsp::FIR::Coefficient have a function called getMagnitudeForFrequency 
But in case of a cascaded filter we have an array of filters with different coefficients… what should I do? Take the average of their response?
Nope, multiply them… they attenuate by a factor, if I understand that correctly
Cascaded means multiplication of linear gains or addition of dB gains
Thanks for pointing that out. getMagnitudeForFrequency are linear gains, right?
Obviously there exist filters like these … since I use them on daily basis in my music production.
Well, no. They may call it “Butterworth”, but that doesn’t make it so. A butterworth is a filter with Q = sqrt(0.5) as said. So it doesn’t make sense to call it a butterworth if it doesn’t have such a Q.
I’m using Juce’s IIR::Filter, but I need something else because it “doesn’t cut sharp enough”
Right, but a single Butterworth is only gonna make that worse 
Anyway, it seems you’re on track - if you need a steeper slope, you have to cascade more filters, or use a different topology.
I asked if anyone could suggest me a library which is capable of this out of the box
I did provide you with several options that do exactly this, but if you’re not having problems cascading the JUCE ones, go with that. Remember that cascading two identical Butterworths does not make a Butterworth of double the order, if you care about filter slopes, resonance shapes and such.
Meanwhile I’m trying to do this cascaded LP+HP thing, but I have dfficulties,
Just in case you missed it, that cascade, should you succeed, is a complex, slow and indirect way of just creating a normal bandpass.
Hi Ivan,
Did you ever make your PlotComponent app available so we can enter design values and get a bode plot for the different filters?
Cheers,
Rail
Well, that class is more or less ready, and will be available in JUCE at some point I guess, but I can’t tell you when since it doesn’t just depend on me 
However, during the DSP workshop I’ll do at ADC, people attending will be able to see and to use a preview of it 
Okay – I’ll just write my own, thanks. It would help to be able to visualize and test the output for the JUCE FilterDesign design methods.
Cheers,
Rail
Hey Rail,
have you succeeded with creating your own filter plotting tool? Otherwise, python + SciPy could help.
Best regards
Kris
Too many projects to do… so I haven’t had time to do this yet. I’d rather stick to using JUCE thanks. I have filter plotting in a few of the projects I’m working on, but I haven’t had the time to create a standalone test tool.
Rail