Filters with Self-Oscillation

#1

I am wondering which filter objects are filters with self-oscillation? I noticed, for example, on SSS's morphMode filter it mentions:

Center position is bandpass, lowest position (negative) is lowpass and highest position (positive) is highpass.
Resonance works in all modes, though only the LP filter has self oscillation.

So persumably with resonance turned up in LP mode you would get a sine output like with an analog fitler? I've tried this and cannot get any output from the filter, I've tried this on a couple, same result no output. Is there something I am missing here?

#2

Hi Dianus, there are a lot of filters in the library and maybe I haven’t checked them all, but I must say that the majority of them have a bad behaviour at extreme value of resonance: distortion, aliasing etc. There are good filters in the community/tiar/filter folder but my favourite is the runge-kutta modelled filter vcf4pole2x in the community/jt/filter folder, it’s not surprising that it takes more DSP resources. You can take it to a beautiful self oscillation if you inject in it a tiny bit of signal, i. e. gaussian noise, so that it’s practically inaudible, with the resonance parameter at 64. SELF_RESO_exp.axp (2.8 KB)

#3

patatos, this was great advice! Adding a little gausian noise through an offset mixer to the input seems to push a few of the filters into self oscillation. Apart from vcf4pole2x here are ones that I tested that also work:

sss/filter/dualvcf3 63.50 res
sss/filter/bppSVF 61.50 res
wp/filter/4polelpf 63 res

vcf4pole2x has the purest sine from the ones I tested so it's the best bet.