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# Filter
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## Basics
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A filter is a circuit which filters out certain parts of the frequency spectrum of the incoming spectrum.
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Filters are named by the spectrum they _cut_ out or _pass_ through:
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- **Lowpass (LP) or Highcut Filter** – cuts away the high frequencies, leaves the low ones
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- **Highpass (HP) or Lowcut Filter** – cuts away the low frequencies, leaves the high ones
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- **Bandpass (BP)** – a combination of LP and HP – leaves stuff around the cuttof frequency, cuts away higher and lower frequencies
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- **Notch** – the inverse of a BP – cuts away stuff around the cutoff frequency, leaves the higher and lower frequencies
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- **Comb Filter** – Nomen est omen
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- ...
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![Different Types of Filters](http://modular.atoav.com/x/Filter_types.png)
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Every filter typically has a well defined Cutoff Frequency – this is the area around which the Filter starts to act.
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Sometimes this area is higher than the rest, this is called "Resonance":
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![Different Types of Filters](http://modular.atoav.com/x/Filter_types_resonant.png)
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## Filters
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There are many different ways to build a filter, each with its own unique character.
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See the Doepfer A-124 Wasp Filter in [this youtube video](https://www.youtube.com/watch?v=A-ZTgWFzDM8)
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See the Doepfer A-106-5 SEM Filter in [this youtube video](https://www.youtube.com/watch?v=4pZDcn6qNn8)
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See the Polivoks VCF in [this youtube video](https://youtu.be/Q5pOU6YaDa0?t=135)
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