Ashly 4.24C manual Delay LCD Display, 6c Delay

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Operating Manual - PROTEA SYSTEM II 4.24C Crossover / System Processor

Parametric EQ (PEQ) uses peak fil- ters with the ability to control boost or cut, frequency center, and bandwidth. Think of one band of parametric EQ as a single graphic equalizer fader except that the frequency is variable, not fixed, and that the bandwidth, or how "wide" the filter affects the frequency spectrum at the center frequency, is com- pletely variable. The smaller the bandwidth, the less the audio signal on either side of the frequency center is boost or cut, whereas a larger "wider" bandwidth produces an audible change to the overall tone of a signal. Para- metric filters are best used to hunt down and eliminate problem feedback frequencies, add or remove a characteristic "hot spot" from mi- crophones, or clean up room resonance situ- ations. It is well worth the time getting pro- ficient with parametric EQ filters, as they offer the best solution to many EQ problems.

Narrow (Low) Bandwidth

W ide (High) Bandwidth

+20dB
+10dB
0dB
-10dB
-20dB
-30dB
20Hz	200Hz	2KHz	20KHz
	4. 24C Parametric Filters

Protea 4.24C parametric filters have a boost/cut range of +15dB to -30dB. There is more cut than boost because one of the more common uses for parametric filters is to dramatically cut, or "notch out", very narrow fre- quencies (low bandwidth) in order to eliminate system feedback problems.

Every instance of a parametric EQ filter has a center frequency selected. The factory default is 1kHz, but each filter's center frequency is adjustable from 19.7Hz to 21.9kHz in 1/24 octave steps. Carefully sweeping a narrow bandwidth filter through a problem feedback area, with just a slight boost, is a quick way to find the exact frequency causing trouble. Once the offensive frequency has been found, cut the filters level, and then the bandwidth is adjusted as narrow as possible while still eliminating the feedback problem. Bandwidth is adjustable from about 1/64 octave to four octaves, and the lower the bandwidth, the less audible the filter action will be. Finding the problem frequency is relatively easy, but finding the best combination of cut and bandwidth takes a little practice. Again, it is well worth the time becoming comfortable with the notching procedure, so that problems can be quickly addressed with a sufficient but minimal amount of correction.

The EQ functions on all four inputs and eight outputs are switched in or out on an individual channel basis. In other words, each input or output has one "switch" for all of its EQ filters. If certain filters are not going to be used within a channel, simply leave the gain for that filter at 0.0dB, and the filter will have no effect.

For an excellent interactive display of the way parametric and shelving filters work, experiment with the 4.24C EQ section of Protea System Software. The software works whether a unit is connected or not, so it is an invaluable teaching tool as well as an audio setup tool for Protea products. The program is shipped with 4.24C units, but is also available on the Ashly web site.

4.6c Delay

Delay LCD Display

In large installations or out-

door venues there are often many speaker clusters in various locations

to get the best coverage possible. Since sound travels relatively slow

through air (1130 ft/s at 20ºC), mul-

tiple loudspeaker locations can create a situation where the original audio signal, simultaneously leaving all loud- speakers, arrives at a single point in the venue at several different times. Needless to say this causes problems, and what may be crystal clear sound directly in front of any one loudspeaker can be a jumbled mess in the farther reaches

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