Reducing feedback in audio systems using the CL-5000
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2.4 Emphasizing Musical Instruments During Recording
Conversely, you can use the CL-5000 to bring out an instrument solo or a lead vocal in a cluttered mix. Match the frequencies
of the equalizer to the frequencies of the instruments to be emphasized (it is best to use a notch filter with a high slope). (Note:
In this application, make sure you only reduce the amplitude of the selected frequencies.) The compression results in a subjective
decrease in the volume of the overall program material. Only the selected frequencies coming from the equalizer remain
uncompressed and are therefore perceived as being louder. This inverse type of compression also helps to emphasize instru-
ments during low-level passages, so that they become more pronounced.
2.5 Reducing Feedback in PA Systems
A common procedure in sound system set-up is equalizing the acoustics to remove feedback. This is generally accomplished by
turning up the system gain to purposely induce feedback, searching for the center frequency of the feedback and then equaliz-
ing at that frequency to remove the feedback. Once this feedback has been attenuated, the system gain is again increased to
induce another feedback point and the whole procedure is repeated until the engineer is satisfied that the relevant problem
frequencies have been corrected. In spite of this equalizing process, feedback remains a difficult problem. Often enough,
acoustic changes occur as the audience enters the room, which again leads to feedback problems. In addition, the frequency
response of the whole system is modified and thus affected by equalizer operation.
Dynamic feedback control is a better solution. Similar to the previously mentioned de-esser application, an equalizer is not
inserted into the audio path but into the sidechain path of the CL-5000. To effectively suppress feedback, the center frequency of
the equalizer is correctly adjusted to match the room’s resonant feedback frequency. This selected frequency now controls the
CL-5000. The signal coming from the equalizer is applied to the DETECTOR LOOP input, while the audio signal is routed
through the CL-5000 audio path. As soon as feedback occurs, the unit temporarily reduces the system gain and thus effectively
suppresses the feedback. In contrast to the technique mentioned above, the frequency response of the PA system is not affected
in any way at all. The use of the CL-5000 in this application can eliminate the possibility of speaker or ear damage.
