Filters…

[Matthew Sanford]

Do filters have to shunt to ground, or could they go to a lower voltage circuit? Say,in 9v circuit could the cap in an LPF go to an op amp using 4.6v so the highs could be used later instead of ground? If so, would it change the characteristics of the LPF?

[fryingpan]

It's not DC voltage, but impedance. Remember that from an AC analysis point of view all DC generators are considered ground.

[fryingpan]

Also, what you are trying to do is essentially a crossover: in essence two separate filters (or a filter + the sum of the inverted filter output and the original signal).

[antonis]

@Matthew: Could you plz post a schematic of what you're trying to do..??

[Matthew Sanford]

@Matthew: Could you plz post a schematic of what you're trying to do..??

Antonis no real specific thing in mind, I generally wade through the vague ideas. For this, say, the high freq. being sent along to be mixed back with the low later (possibly LFO panning between them or something). Frying pan brings up the point though, I could have the LPF and HPF break from the same point like a BMP tone stack but not end at the blending pot - and I suppose the high frequencies would need to go through a cap first with R to ground to be proper anyway? Just wasn't sure if towards lower voltage would be as good as ground, but DC vs AC it is? on that, so the lack of impedance in ground is truly what takes the highs off an LPF?

Just one of the many random odd possible applications my brain goes on in the background, like learning on optocouplers has me thinking of using them as the diodes in a distortion with the transistors taking from there to use somewhere else - in that case, I guess it would be similar to the original signal but not distorted as it goes through the LEDs?

[antonis]

but DC vs AC it is?

Not at all..
Just AC..
(forget all about DC or implement superposition theorem - which results into equivalent outcome for DC sources considered GND)

[Matthew Sanford]

superposition theorem...need to learn... first definition I find "In any linear and bilateral network or circuit having multiple independent sources, the response of an element will be equal to the algebraic sum of the responses of that element by considering one source at a time.", with pictures of where the current goes, and how much voltage across resistors. I think I'm getting it, to understand where all voltage and current lies and where it travels so you then know what everything is at each point.

I need to read more on it all, AC can consider a voltage source as ground right, and caps 'see' things differently too, and all that stuff. Thank you for coddling me 

[FiveseveN]

[Matthew Sanford]

Brilliant, thank you, will pick up at 7 minutes as it is all great info! Also reminded me, the filter is actually a frequency dependent divider, doi. And helped me to realize it's all C but the D and A just signify the speed of wobbles and isn't really that different otherwise...

[ElectricDruid]

Also reminded me, the filter is actually a frequency dependent divider, doi.

Absolutely this. When you get this, you can suddenly see why the lowpass is RC and the highpass is CR.

[Matthew Sanford]

...see why the lowpass is RC and the highpass is CR.

Aye yai yai! You and all your sensible sensical sense! Now to hope it does not fall from brain...