How does a ladder filter work?

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How does a ladder filter work?

Postby decklyn » Sat Feb 24, 2018 12:41 am

I went off the deep end and started building synth gear like crazy.
I can understand most of the components of the synth fairly easily - egs, lfos, vcos, for example are fairly easy to understand.
The filter to me is a complete mystery. I was chatting with a colleague today about how to frame this. How does a square turn into a sine, and we came to the conclusion that it's better to think of the harmonics that are cut rather than thinking of the waveform. And the resonant bump as an increase in harmonics at the point that the filtering starts and then cutting harmonics above/below.

But I'm wondering if someone can help me understand exactly HOW eg a ladder filter achieves this through voltage control. It's really hard for me to wrap my head around and intuit. My friend has an educational background in electrical engineering but he's doing mostly digital and smd work - he could not explain how these things work to me :( so hoping I can get some help grokking this here!
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Re: How does a ladder filter work?

Postby synthchaser » Tue Feb 27, 2018 11:06 pm

I'd recommend reading the active filter cookbook by Don Lancaster. A great book that covers active (transistor-based) filters in detail.
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