Filter - Waldorf Q Keyboard User Manual

Sound Parameters – Filter

Filter

Once the audio signal leaves the mixer, it is sent to the filters. The Q has two independent filter units,
each with its own individual settings. The signal flow in the filters can be controlled in the Routing
section. The filters are components that have significant influence on the Q's sound characteristics.
For a detailed description of the different filter types that are available in the Q, see the section "Filter
Types". For now, we explain the basic function of a filter with the filter type that is used most
commonly in synthesizers: the low pass filter.
The low pass filter type dampens frequencies that lie above a specified cutoff frequency. Frequencies
below this threshold are hardly affected. The frequency below the cutoff point is called the pass band
range, the frequencies above are called the stop band range. The Q's filter dampens frequencies in
the stop band with a certain slope. The slope can be 12dB or 24dB per octave. This means that the
level of a frequency that lies an octave above the cutoff point will be 12dB or 24dB less than those
frequencies of the signal that fall into the pass band.
Level
Frequency
Cutoff
Picture 23: Low Pass Filter principle
To give you an idea of the extent of damping, consider this example of a low pass filter: A reduction
of 24dB reduces the original level one octave above the cutoff point by approx. 94%. The damping
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 is no longer audible.
The Q's filter also features a resonance parameter. Resonance in the context of a low, band or high
pass filter means that a narrow frequency band around the cutoff point is emphasized. The following
picture shows the effect of the resonance parameter on the filter's frequency curve:
Level
Resonance
Frequency
Cutoff
Picture 24: Low Pass Filter Resonance
85 Waldorf Q User's Manual