More Filter Diversity

[BobF]

BobsSpectralCrossOver Filter.fsm

(659.01 KiB) Downloaded 1035 times

Hello Gang,
After introducing my “Dual Peak Band Pass Filter”( viewtopic.php?f=3&t=36908#p110264), I remembered a filter produced by Nyle Steiner back in 1974. https://electronicmusic.fandom.com/wiki/Steiner_filter.
I liked the idea of the inputs being LP, HP, and BP and not the outputs. Now I am NOT a coder so I had to figure out another option other than the Sallen Key configuration Steiner used (maybe someone else could do this), so I started to play around with stream addition, subtraction, and inversion on the inputs and outputs of Low Pass and High Pass filters till I came up with this configuration that seems to work with all Low Pass and High Pass filters we use here in FLOWSTONE. I picked my Dual State Variable because I did want 24 db roll off. The demo consists of the schematic for the input and output, the configuration added to a dual state variable filter set to low pass only with a crossfader on the input. Play with the crossfader and cutoff to see want they do. Notice with various settings of the crossfader you can get some shelf filter responses. Next is the same configuration with two sine wave inputs at different frequencies. I call this “Spectral Crossover” as you can sweep from Low Pass to High Pass, passing from one frequency to the other and with more harmonic waveforms (Saw, Square, etc.) from one set of harmonics to the other. I added in/out switches to both LP and HP inputs so you can experiment some. Last is a normal Dual State Variable filter for comparison.
Remember even though this is a working configuration with the “Dual State Variable”, again you can add this Low Pass, High Pass, and Band Pass input configuration to any Low Pass or High Pass filter found on the Flowstone forum (at least I believe so, I probably missed some, but did test a lot of them).
Have fun, and let me know if you discover anything new or have more ideas of your own!
Later then, BobF…..

[Duckett]

Very cool stuff. Many thanks!

[Spogg]

Very interesting idea Bob!

I know almost nothing about filters so I normally just listen, because looking at spectra doesn’t help me to anticipate what sound will happen.
Because of this, it would be really nice if you could knock up a really simple synth so I could play it and hear the results. Nothing fancy; oscillators, env and your filters to switch between.

Cheers

Spogg

[trogluddite]

Thanks's Bob - it great to see something new being done with filter topologies besides the tweaking of different DSP/ASM code models. The icing on the cake is that it uses so few components and can be adapted to whatever filter you prefer to use.

I think that being able to use the same filter to LP one oscillator while applying HP to another could add another string the bow of all sorts of synths. There might be some inter-modulation distortion in that case, so it might not suit "mastering EQ" for folks with golden ears; but in synths, we do that on purpose all the time to make sounds more "interesting" (e.g. FS/AM/Ring-mod'), so I reckon it would definitely be a "feature" rather than a "bug" if it were added as an extra filter mode.

[wlangfor@uoguelph.ca]

Thanks for this, I will be sure to study it

[BobF]

Here is a demo Synth using the "LP/HP Spectral Crossover Filters" as Spogg suggested. Enjoy!

BobsSprectralCrossoverFilter Demo.fsm

(878.59 KiB) Downloaded 994 times

Later then, BobF.....

[Spogg]

Thanks for taking the time to do that Bob.

Now I can hear it, and I’m impressed by what it does.
I suspect the phase shifts in the filter contribute significantly to the sound, but I’m a dunce when it comes to such things.

Many thanks again Bob

Spogg