Filter
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19
OPTIMIZER
level changes due to dramatic boost or cut adjustments.
The Notch switch puts the filter into notch filter mode. It
provides a deep cut of over 60dB which can be varied in fre-
quency to address any part of the audio spectrum, providing
in excess of 60dB of attenuation at the center frequency. The
Q control varies the bandwidth of the notch from narrow to
wide, while the roll-off control may be used to select either a
steep or gentle roll-off at each side of the notch.
The Notch filter is useful in corrective applications where
it can be used to attenuate mains hum and similar ‘pitched’
interference. Because mains hum contains harmonics, better
results are often achieved by using two Notch filters
together, one tuned to the fundamental frequency and one
an octave higher. The narrower the notch, the less the wan-
ted sound will be affected by the filtering. Notch filtering
also can be used to simulate phasing by manually sweeping
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