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SOUNDSHAPER: CDP REFERENCE

FILTER - spectral filter


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SPECTRAL > FILTER > FILTER >

SUMMARY
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. 

© Ensemble Software and Composers Desktop Project 2014