What are the Types of Filters?

[Casmat]

Greetings fellow HISEr!

I’m in a bit of a pickle, and I need a mighty HISE hero to help me be free! Hoorah!!! To accomplish this difficult task, thou must teach me, the different types of filters! As I was taking a gander through the different nodes in scriptnode after searching “filter”, I was swashbuckled and perplexed. There’s svf’s (think I’ve heard of them), biquads, and more weird filters (moog?), what even is a linkwitzriley??? I’m absolutely bewildered! Ultimately, I am trying to find the differences and similarities between all these filters! Alongst with which one is the best to use? O, which great hero shall this day's woes abate? Shall it be thou, fairest of the fair?

Farewell!

P.s. Shakespeare sucks
Don’t feel offended..

[Dan Korneff]

The State Variable Filter is capable of producing various filter responses from its state variable. You'll see that it has a cutoff frequency and resonance that use the same state. The Biquad Filter is created by a second-order linear differential equation. You can use it for all sorts of things, from lowpass, highpass, bandpass, notch and peak. The Moog Filter is a classic ladder filter. It has a warm, and resonant character. The Linkwitz-Riley filter is a crossover filter with the ability to maintain a flat amplitude response when summed. Hope this helps answer your question.

[Casmat]

@Dan-Korneff Interesting, thanks HISE hero! What do you use most of the time?

[aaronventure]

@Casmat Not who you asked, but there's no right answer here, it depends on your use case.

Do you need to do multiband DSP processing? Use Linkwitz-riley to split your signal into bands (you can verify that it's mathematically correct when summing by comparing the input with the phase inverted sum, which should get you a perfect silence). Do you need an oldschool synth filter? Use the Moog.

Etc. Etc. I suggest some reading on DSP and filters. I'm sure most DSP books will cover this in one way or the other, but if you want to learn about filters specifically, give this a try https://www.native-instruments.com/fileadmin/ni_media/downloads/pdf/VAFilterDesign_2.1.0.pdf

This is a very dense work but you don't need to understand all the math stuff to get a grasp at the theory and looking at the charts. If you play along with the available filters and examine the results on a frequency analyzer, you'll get a good idea of what they do. Of course if you understand the math here then this might be an interesting rabbit hole to get lost in for a few days/weeks.

[Casmat]

@aaronventure cool! Thanks!