Filter
Basics
A filter is a circuit which filters out certain parts of the frequency spectrum of the incoming spectrum. Filters are named by the spectrum they cut out or pass through:
- Lowpass (LP) or Highcut Filter – cuts away the high frequencies, leaves the low ones
- Highpass (HP) or Lowcut Filter – cuts away the low frequencies, leaves the high ones
- Bandpass (BP) – a combination of LP and HP – leaves stuff around the cuttof frequency, cuts away higher and lower frequencies
- Notch – the inverse of a BP – cuts away stuff around the cutoff frequency, leaves the higher and lower frequencies
- Comb Filter – Nomen est omen
- ...
Every filter typically has a well defined Cutoff Frequency – this is the area around which the Filter starts to act.
Sometimes this area is higher than the rest, this is called "Resonance":
Filters
There are many different ways to build a filter, each with its own unique character.
See the Doepfer A-124 Wasp Filter in this youtube video
See the Doepfer A-106-5 SEM Filter in this youtube video
See the Polivoks VCF in this youtube video