A Quick Tour of UniQuest For EWI 4000s
UniQuest for EWI 4000s 21 of 44
Q-FACTOR
•Range is 0.5 to 12.7. This control sets the Quality Factor of the OSC FILTER,
and is analogous to the RESONANCE control found in typical analog synthe-
sizer filter sections.
The Q Factor of an audio filter is defined as the cutoff frequency divided by the
bandwidth (the 3dB change in level around the cutoff frequency). While this sounds
complicated and rather mathematical, it is easier to understand by comparing how
the frequency response curve of a lowpass filter changes with different Q factors:
As can be seen, higher Q Factors mean the filter passes more signal around the cut-
off frequency while stopping more signal content outside this bandwidth. This also
makes the filter more resonant at higher Q factors, which is why the control can also
be thought of as a ‘Resonance’ parameter.
KEY FOLLOW
•Range is -12 to 24. When this control is set to 0, the filter’s cutoff frequency
remains the same for any note played. For all other values of KEY FOLLOW, the
filter’s cutoff frequency will be changed based on the current note.
Note number 72 (which is MIDI Note C 6, and the starting note shown in the 5th
octave of the LCD keyboard display) is the reference point for the filter cutoff fre-
quency: No matter what value KEY FOLLOW is set to, the filter’s cutoff frequency
will apply for this note:
Positive KEY FOLLOW settings will cause the cutoff frequency of the filter to be
raised for notes higher than C6 and lowered for notes lower than C6. Negative set-
tings have the opposite effect. When KEY FOLLOW is +/- 12, the tracking slope is
1:1 or -1:1 respectively, meaning that the cutoff frequency will be shifted by the
same frequency amount as the the note (relative to C6). This produces a very musi-
cal effect.