User`s manual

Page 28
A Closer Look at the NF575 Plug-In
Filter Slopes
Although there are several ltering options available for the Pro Tools™
platform, few, if any, have the precision of the NF575 Noise Filter. Not only
designed for the ultimate in ltering accuracy, the high pass and low pass lters
included in the NF575 have slopes up to 36dB/Oct. Because of the steepness of
the NF575 Noise Filter high pass and low pass lters, even greater amounts of
noise reduction are possible. The transition (slope) between unaffected and
ltered frequencies allows even tighter control over audio signals and the noise
removal process.
Notch Filter Soloing
Great notch ltering is nearly useless if the cyclical noise cannot be monitored
accurately. The notch lter solo buttons use band pass lters in place of the
notch lters, so the user can audition cyclical noise sources over a selectable
frequency bandwidth. When a notch lter band is soloed, the Q control still
affects the lter, and the lter is the exact opposite of the notch. The user is
effectively listening to the removed signal when a notch lter is soloed.
Note the Solo control only solos the lter band by as much as the Range value.
When the Range control is at its maximum reduction, the band will be soloed
the most. When the Range control is at its minimum reduction (no reduction)
the Solo control has no effect.
For each notch lter band, soloing that band and sweeping it across its available
frequency control range will reveal at what frequency the noise source is the
loudest. Upon nding this loudest frequency location, un-solo the notch lter,
and that cyclical noise is now absent from the audio signal. Adjust the Q control
as tightly as possible to remove only the noise and not the desired audio data.
Repeat this process for all notches, or until all audible cyclical noise is removed.
Notch Filter Linking
Sometimes the cyclical noise has a fundamental frequency, but the harmonics
of the periodic noise also contaminate the audio. By linking all the notch lter
frequencies to the rst notch lter band in the NF575, cyclical noise can be
quickly removed. Default settings put the notch lter frequencies at harmonic
intervals automatically (ex: 60, 120, 180, 240, 300 Hz). And if the noise does
not contain harmonics, but rather seemingly unrelated cyclical noises at various
frequencies, the NF575 notch lters can be linked at any frequency interval (ex:
120, 168, 240, 328, 400 Hz).