User`s manual

57
4.4.4: 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 0 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 60dB). 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.
Description of controls is as follows:
Cutoff Frequency: Specifies frequency in Hertz below which all signals are attenuated.
Frequencies above this cutoff are unaffected. Minimum Cutoff Frequency is 0
Hz (no frequencies attenuated), while the maximum Cutoff Frequency depends
upon the System Bandwidth setting. Cutoff Frequency can be adjusted in 1 Hz
steps
Stopband Specifies amount in dB by which frequencies
Attenuation: below the Cutoff Frequency are ultimately attenuated. Stopband attenuation is
adjustable from 10dB to 60dB in 1 dB steps.
Figure 4-21 Highpass Filter Control Window