User`s manual

75
4.4.11: Multiple 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, e.g. telephone
“DTMF” tones.
The Multiple Slot filter is used to isolate, or "slot", up to 16 single-frequency signals, such as
tones or whistles, from the input audio, eliminating all other audio. This is the exact opposite
of the Multiple Notch filter function, and is accomplished using a frequency-sampling-
synthesized 1024-tap FIR filter which is calculated in the PC by the PCAP II Plus Master
Control program.
To properly utilize the Multiple Slot filter, you will first need to identify the frequencies of all
signals 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 frequencies of the signals have been identified, set the Slot Freq(uency) of each slot
to be used to the desired signal frequency.
Usually, the signal frequencies will not remain constant but will vary slightly due to
modulation, wow and flutter, and acoustic "beating". Therefore, you may need to increase the
Slot Width of each slot from its minimum setting to avoid having the signal move in and out of
the slot.
Once all the Slot Freqs and Slot Widths have been entered, you will need to build the actual
filter using the Build command. Like the Multiple Notch Filter, this filter is also constructed
in the computer. A brief delay occurs after Build before it takes effect.