dbx PX User Manual page 17

DriveRack
• You will now use the <DATA> wheel to select the number of fixed filters. This will range
from values 0-12. The total number of filters will stay at 12, and the number of live
filters will be = Total Num Filters – Num Fixed. Live and Fixed filter types differ in
that FIXED mode filters are automatically assigned to a frequency creating feedback,
thus remaining at that frequency until cleared by the user. In LIVE mode, live filters
automatically detect and remove feedback frequencies in the presence of audio (music
or speech). When all of the live filters have been used, they begin to round robin.
Essentially this means that the first filter set is replaced where a new feedback is
detected and notched out. This mode is useful because feedback frequencies may change
as the microphone is moved, and/or as the characteristics of the venue change.
The Fixed/Live filter usage will be indicated at the bottom of each page of the AFS menu.
'F' indicates an available fixed filter, and 'L' indicates an available live filter. A blocked
out F or L indicates a filter that is set, or in use. Once the desired number of fixed filters
has been selected, press the <NEXT PG> and the display will read:
• These types pertain to the Q, sensitivity, and algorithm type. The filter is established
by using the formula: Q= Freq divided by Bandwidth. This means that a higher Q will
produce a filter that is more narrow. Values are: Speech (Bandwidth = 1/5 octave and
Q=7.25), Music Low (Narrow notch filter, Bandwidth = 1/10 octave and Q=14.5), Music
Medium (Very Narrow notch filter, Bandwidth = 1/20 octave and Q=29), Music High (Ultra
Narrow notch filter, Bandwidth = 1/80 octave and Q=116). To guarantee that feedback
is suppressed at lower frequencies, the AFS may place wider notch filters at these lower
frequencies (below 700 Hz). Once the desired fixed type has been selected, press the
<NEXT PG> button and the display will read:
• You are now prompted to raise the output gain of the mixer to the level of the
performance. Once the desired level has been set and all of the fixed filters have been
assigned, the unit will automatically move you to the page that indicates the fixed filter
setup has been completed. If you have reached the performance level setting and all
of the fixed filters have not been used, you may want to return to the page that selects
the number of fixed filters and re-adjust the number of fixed in order to provide you with
additional live filters. Regardless, once you have completed the setup, the display will
read:
®
PX
®
Getting Started
Section 2