Technical information

APPENDIX 12
The NF575 Noise Filter is a high-resolution  lter set designed to remove a wide
variety of noise types from audio.
The NF575 Noise Filter o ers much greater precision than most other  lter
sets available for Pro Tools using a specially designed set of algorithms for
removing unwanted noise from audio with as little effect on the original
audio as possible. Selectable slopes of 6, 12, 18, 24, 30, and 36 dB/octave and
a frequency control range covering the entire audible spectrum make the
NF575 filters extremely flexible. All five NF575’s notch filters can be linked
harmonically to remove common cyclical noise.
The top half of the NF575 user interface has an input level control at the left
and an output level control at the right with phase reversal switches for each
output channel underneath this. Between these level controls, there is a large
frequency response display, with a set of bar graph meters for input and
output levels to the right of this.
The lower half of the user interface contains the controls for the  lters. At the
left you will  nd a high-pass  lter and at the right a low-pass  lter. These both
have rotary controls for Q (bandwidth) and Frequency, and there is a small
bypass button for each  lter underneath these controls.
The high-pass filter is useful for removing low-frequency rumble, plosive
sounds from vocals or speech, and other unwanted low frequencies. The
low-pass  lter is useful for removing background hiss, wind, and other high-
frequency noise.
In between the high-pass and low-pass  lters, there are  ve notch  lters, each
with rotary controls for Q, Frequency, and Range. The Range control is used
to adjust the amount of signal reduction at the notch  lter Frequency. The
bandwidth (Q) of each notch  lter can be made extremely narrow to remove
the noise while a ecting the remaining audio as little as possible.
The frequency controls of all the notch  lters can be linked at any frequency
interval (e.g. using a harmonic or other relative o set). If you click the link
button, located just to the left of the  rst notch  lter’s frequency control, the
frequency controls for  lters 2 to 5 become linked to this. With the controls
unlinked, you can set the intervals between adjacent notches. Then, with
the controls linked, you can use the  rst frequency control to move all the
frequencies up or down while preserving the intervals between the notches.
Each filter also has a bypass button and a Solo button located below the
rotary controls. The Solo buttons can be used to help identify unwanted noise
frequencies. When you enable a Solo button, the  lter shape  ips from band-