User`s manual

68
4.4.8: Notch Filter
Application:
The Notch filter is used to remove, or "notch out", a narrow-band noise, such as a tone or a
whistle, from the input audio with minimal effect to the remaining audio. The Notch filter
works best with stable noise sources which have constant frequency; if the frequency of the
noise source varies, then the 1-Channel Adaptive filter is recommended.
To properly utilize the Notch filter, you will first need to identify the frequency of the noise;
this is best done using the Spectrum Analyzer window. See Section 4.8.2: for complete
instructions on operating the Spectrum Analyzer window.
Initially set the Notch Depth to 60 dB and the Notch Width to the narrowest possible value.
Next, set the Notch Frequency to the noise frequency. Fine adjustment of the Notch Frequency
may be necessary to place the notch precisely on top of the noise signal and achieve
maximum reduction of the noise. This is best done by adjusting the Notch Frequency up or
down 1 Hz at a time while listening to the Notch filter output on the headphones.
Often, the noise frequency will not remain absolutely constant but will vary slightly due to
modulation, recorder wow and flutter, and acoustic "beating." Therefore, you may need to
increase the Notch Width from its minimum setting to keep the noise within the notch.
For maximum noise reduction, set the Notch Depth to 60dB. It is best to adjust the Notch
Depth up from 60 dB until the tone is observed, then increase the depth 5 dB.
Description of controls is as follows:
Notch Frequency: Specifies frequency in Hertz which is to be removed from the input audio.
Minimum Notch Frequency is 10 Hz, while maximum Notch Frequency
Figure 4-29 Notch Filter Control Window