Though implemented in the frequency domain, this filter has a traditional selection of filter types and controls. MODES 1/2/5. High Pass: Filter frequencies below cutoff frequency (Freq1). Mode 2 normalizes result and Mode 5 adds Gain control. 3/4/6. Low Pass: Filter frequencies above cutoff frequency (Freq1). Mode 4 normalizes result and Mode 6 adds Gain control. 7/8/9. Band Pass / Notch: For Modes 7/8 Bandpass, filter frequencies outside frequency band (Freq1-Freq2). For Mode 9 Notch, filter frequencies inside frequency band (Freq1-Freq2). Mode 8 normalizes result. PARAMETERS freq1 The cutoff frequency, or (in Band/Notch Modes 7-9) the lower limit of the frequency band. For High Pass, frequencies are filtered below this frequency; for Low Pass, they are filtered above it. Range: 10-22050 Hz T-V
freq2
Band Pass / Notch
(Modes 7-9) only: the upper limit of the frequency band.
Frequencies
are filtered outside the band in Band Pass modes, while in
Notch mode
it is the band itself that is filtered.Range: 10-22050 Hz. Freq2 must be higher than freq1. T-V
bandwidth
('Q') The filter's sharpness, in Hz.
Controls the steepness of the decay above/below freq1 and freq2
(as appropriate). Smaller=
narrower "skirts"
(more focused filter). The decay
of amplitude
is from freq1 to freq1+bandwidth
(Low-pass); from freq1 to
freq1-bandwidth (High-pass); and from freq1 to
freq1-bandwidth as well as freq2 to freq2+bandwidth
(Band-pass/notch).
Range: 1-22050 Hz. T-V
gain Amplify
or
lower the level of the output sound. As filtering reduces
the level of
the signal, you may wish to raise the output level
here. Range:
0.001-1-10000,
default 1.
![]() Illustration of 'brickwall' low-pass filtering: smallest possible 'Q' value at 440Hz. cut-off NOTES By working in the frequency domain, the program is capable of very precise and very sharp filtering. The bandwidth of the filter "skirts" ('Q') is also time-variable. With time-varying freq1 (and freq2), various filter-sweep effects are possible.
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