User`s manual

59
4.4.5: Bandpass Filter
Application:
The Bandpass filter is used to decrease the energy level (lower the volume) of all signal
frequencies below a specified Lower Cutoff Frequency and above a specified Upper Cutoff
Frequency, thus combining the functions of a Lowpass and Highpass filter connected in series
into a single filter. The signal region between the Lower Cutoff Frequency and the Upper
Cutoff Frequency is called the passband region. The Bandpass filter is useful for
simultaneously reducing both low-frequency rumble and high-frequency hiss.
The Lower 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 Lower 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 Upper Cutoff Frequency is usually set above the voice frequency range (somewhere
above 3000 Hz) so that the voice signal will not be disturbed. While listening to the filter
output audio, the Upper Cutoff Frequency, initially set to its maximum frequency, can be
incrementally lowered until the quality of the voice just begins to be affected, achieving
maximum elimination of high-frequency noise.
The amount of volume reduction outside the passband region 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 each Cutoff Frequency) to the minimum
volume (specified by Stopband Attenuation) can also be controlled by adjusting the Transition
Slope setting.
Figure 4-23 Bandpass Filter Control Window