Waldorf AFB 16 User Manual - How Does A Filter Work?

      Basic Operation AFB16

15

AFB16 User´s Manual

How does a filter work?

The AFB16 is equipped with 16 analog low pass filters.

The low pass filter type dampens frequencies that lie

above a specified cutoff frequency, and frequencies

below this cutoff point are allowed to pass through

unaffected. The frequencies below the cutoff point are

referred to as the “pass band range”, and the frequencies

above are called the “stop band range”. The AFB16´s

filter dampens frequencies in the stop band with a slope

of either 12dB or 24dB per octave. This means that the

level of a frequency that lies one octave above the cutoff

point will be either 12dB or 24dB lower than the level of

those frequencies of the signal that fall into the pass band

range. The following picture shows the basic principle of

a low pass filter:

Low Pass Filter principle

To give you a more specific example of the dampening

effect, consider this: a reduction of 24dB reduces the

original level one octave above the cutoff point by

approximately 94%. The dampening factor two octaves

above the cutoff point reduces the original level by more

than 99%, which in most cases means this portion of the

signal will no longer be audible.

The AFB16’s filter also features a Resonance parameter

(also called “emphasis”). In the context of a low, band or

high pass filter, resonance means that a narrow frequency

band around the cutoff frequency is emphasized. The

following picture shows the effect of the resonance

parameter on the filter’s frequency curve: