Lowpass
[Audio Filters]


Detailed Description

The lowpass audio filter is a filter to attenuate sounds in the audio track that are higher than the cutoff frequency. In other words, low frequencies are passed by the filter, and high frequencies are stopped.

Example Usage:

  sc = Flix2_AddFilter(&filter, flix, FE2_FILTER_LOWPASS);
  // Cut off frequencies above 10khz
  if(sc == ON2_OK)
      sc = Flix2_FilterSetParam(filter, FE2_LOWPASS_CUTOFF, 10000.0);

Additional References:

Cookbook formulae for audio EQ biquad filter coefficients by Robert Bristow-Johnson


Defines

#define FE2_FILTER_LOWPASS
 Filter name for use with Flix2_AddFilter().
#define FE2_LOWPASS_Q
 Filter parameter for shape constant ("Q" coefficient).
#define FE2_LOWPASS_CUTOFF
 Filter parameter for cutoff frequency.

Define Documentation

#define FE2_FILTER_LOWPASS

Filter name for use with Flix2_AddFilter().

Definition at line 46 of file lowpass.h.

#define FE2_LOWPASS_CUTOFF

Filter parameter for cutoff frequency.

This is the filter's "corner" frequency. Components of the sound track with frequencies higher than this frequency will be attenuated. If very precise control of the cutoff frequency is required, note that the response of the filter at this frequency is -3db. Note that the maximum frequency is always half of the sampling rate of the produced file (5512.5/11025/22050 for sample rates Hertz11025/Hertz22050/Hertz44100 respectively).

Definition at line 69 of file lowpass.h.

#define FE2_LOWPASS_Q

Filter parameter for shape constant ("Q" coefficient).

The Q coefficient controls the "shape" of the filter. In general, higher numbers mean a sharper response curve. The default value is 0.707, and should be appropriate in most cases. If you feel the default value is inadequate, iterative experimentation is the best way to select a new value. Alternatively, a mathematical description of this filter is linked in the references above.

Definition at line 57 of file lowpass.h.


On2 Technologies, Inc Flix Engine Linux documentation, generated on Tue Nov 2 16:53:00 2010 by doxygen 1.5.5