Filtering attenuates (lessons) the low or high frequencies of a sound.
How to use it
Selecting Filter from the menu will bring up a dialog box with the following three parameters, Filter, Low Pass, High Pass and Normalize. The default parameters will do a small amount low pass filtering.
The Filter field can have a range of 0 to 100%. It controls the amount of filtering. Generally the more a sound is filtered, the more the amplitude drops.
With the Low Pass radio button selected, the high frequencies will be attenuated at -12 dB per octave.
With the High Pass radio button selected, the low frequencies will be attenuated at -12 dB per octave.
When the Normalize check box is selected, the sound will be amplified to the level before it was filtered. When selecting Normalize, you may not get what you expect. For example, when applying a high pass filter to a sound with no high frequencies, there will be no high frequencies to pass through the filter, so all you get is an amplitude drop from filtering out the low frequencies. Normalize boosts the amplitude up to were it was, and it looks like the filter didn't do anything, but it did, Normalize just canceled out the filtering effect.
Notes
To make the filter slope -24 dB per octave, filter the sound again with the same parameters. Filter it again for -36 dB per octave.
