User`s manual

73
4.4.10: Slot Filter
Application:
NOTE: The Slot filter has very little use in speech enhancement applications; the main
value is in isolating other types of signals that are non-speech in nature.
The Slot filter is used to isolate, or "slot", a single-frequency signal, such as a tone or a
whistle, in the input audio, attenuating all other audio. This is the exact opposite of the Notch
filter function.
To properly utilize the Slot filter, you will first need to identify the frequency of the signal to
be isolated; this is best done using the Spectrum Analyzer window. See Section 4.8.2: for
complete instructions on operating the Spectrum Analyzer window.
Once the frequency of the signal has been identified, initially set Stopband Attenuation to 60
dB and the Slot Width to the narrowest possible value. Next, set the Slot Frequency to the
signal frequency. Fine adjustment of the Slot Frequency may be necessary to place the slot
right on top of the signal. This is best done by adjusting the Slot Frequency up or down 1 Hz
at a time while listening to the Slot filter output on the headphones.
Usually, the signal frequency will not remain constant but will vary slightly due to
modulation, recorder wow and flutter, and acoustic "beating". Therefore, you may need to
increase the Slot Width from its minimum setting to avoid having the signal move in and out
of the slot.
To optimize background noise reduction for your application, set the Stopband Attenuation to
60dB. If, however, you wish to leave a small amount of the background noise mixed in with
the isolated signal, adjust the Stopband Attenuation to the desired value.
Figure 4-33 Slot Filter Control Window