So, a 2-pole filter refers to a filter with a 12dB/octave slope, while a 3-pole filter has a 18dB/octave slope and so on. This is just a way of defining the slope of the filter in 6db/octave steps. You will often see on synths an indication regarding the number of “poles” the filter has: 2-pole, 3-pole, etc. Thus, the boost produced by a filter with a 12db/octave slope will be twice as high as that produced by a filter with a 6db/octave slope. The more decibels, the more drastic the attenuation. The attenuation that takes place is expressed in decibels/octave. The slope of the filter determines how severe the process will be. It is from this frequency ─ or sometimes right below it, depending on the filter ─ that the other frequencies are cut (although “attenuated” would be a more correct description). The cut-off frequency is a frequency defined by the user of the filter, usually with a potentiometer. Common characteristicsĪll filters work by the combination of one or more “cut-off” frequencies and a “slope.” There are different types of filters, depending on the frequency range you want to cut or boost: Low-pass filters, high-pass filters, band-pass filters, and notch filters.īefore analyzing their differences, let’s first take look at their similarities. But I can tell you already that the idea behind it is to shape sound starting with a signal that is rich in harmonics, which you can remove or highlight…thanks to filters! We’ll come back to subtractive synthesis later.

High pass vs low pass filter