[sdiy] HP from LP ?

[Michael Zacherl]

Hi,
I discussed that briefly in one of the last SDIY meetings,
did some experiments but never came to a sound conclusion:

Is there a ‘cheap’ way of turning a low pass filter into a high pass?

How’s that possibly approached? 
Just something like subtracting the LP’s output from its input signal?
If so, what about resonance?

My point about doing that cheaply is the (upcoming) release of two synths with Moog ladder filter featuring a switchable high pass mode.
To my knowledge, there was no resonating HP filter from Moog so far in any synth. 
Until now.
Since both synths (Moog Mother-32 and Behringer Model D) are on the budget side in terms of money I’d rather expect a simple solution compared to a, say, DSI Pro-2 with two fully featured filters in it.

Any hints?
Thanks, Michael.


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