User`s manual

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Stopband Specifies amount in dB by which frequencies above
Attenuation: the Cutoff Frequency are ultimately attenuated. Stopband attenuation is adjustable
from 0dB to 90dB in 1 dB steps.
Transition Specifies slope at which frequencies above the
Slope: Cutoff Frequency are rolled off in dB per octave. Sharpest roll off occurs when
Transition Slope is set to maximum, while gentlest roll off occurs when Transition
Slope is set to minimum. Sharp roll-offs may cause the voice to sound hollow but
will allow more precise removal of high frequency noises. Note that the indicated
value changes depending upon Cutoff Frequency.
A graphical description of the lowpass filter and its controls is given below.
Figure 7-3: Lowpass Filter Graphical Description
7.3 Highpass filter
Application:
The Highpass filter is used to decrease the energy level (lower the volume) of all signal
frequencies below a specified Cutoff Frequency, thus reducing low-frequency noises, such as
tape or acoustic room rumble, from the input audio (The Highpass filter is sometimes called a
"rumble filter").
The Cutoff Frequency is usually set below the voice frequency range (somewhere below 300 Hz)
so that the voice signal will not be disturbed. While listening to the filter output audio, the Cutoff
Frequency, initially set to 100 Hz, can be incrementally increased until the quality of the voice just
begins to be affected, achieving maximum elimination of low-frequency noise.
The amount of volume reduction below the Cutoff Frequency can further be controlled by
adjusting the Stopband Attenuation setting (maximum volume reduction is 90dB). The slope at
which the volume is reduced from normal (at the Cutoff Frequency) to the minimum volume
(specified by Stopband Attenuation) can also be controlled by adjusting the Transition Slope
setting.
Figure 7-4: Highpass Filter Control Window