Ashly Protea DSP360 Manuel d'utilisation - Page 7

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Operating Manual - PROTEA™ DSP480 and DSP360 System Processors

whereas a larger "wider" bandwidth produces an

audible change to the overall tone of a signal.

Parametric filters are best used to hunt down

and eliminate problem feedback frequencies,

add or remove a characteristic "hot spot" from

microphones, or clean up room resonance situa-

tions. It is well worth the time getting proficient

with parametric EQ filters, as they offer the best

solution to many EQ problems.

Protea 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 frequencies

(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 DSP480 or

DSP360 EQ section of Protea NE Software. The software works whether a unit is connected or not, so it is an invaluable teach-

ing tool as well as an audio setup tool for Protea products. The program is available on the Ashly web site.

4 .6c Delay

In large installations or outdoor

venues there are often many speaker

clusters in various locations to get the

best coverage possible. Since sound trav-

els relatively slow through air (1130 ft/s

at 20ºC), multiple loudspeaker locations

can create a situation where the original

audio signal, simultaneously leaving all loudspeakers, 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 unintelligible

in the farther reaches of the venue with direct line-of-sound to multiple loudspeakers. The solution is to delay the audio signal

to the loudspeakers located beyond the main stage area, so that sound comes out of the distant loudspeakers at the exact time

that sound from the main stage loudspeakers arrives. Up to 682 milliseconds of time delay are available, allowing secondary

loudspeaker clusters to be time aligned with the primary speakers up to 771 feet (235m) away from the main stage area.