Note: this post is from 2006, outbound links may be broken.
Jeff Rippe releases HyperFilter
HyperFilter is a high frequency filter with a selectable cutoff slope of -12, -24 or -36dB/Octave.
The filter is extremely useful for removing hiss, crackles and even sampling noise from your audio. The filter has 2 controls: cutoff slope and cutoff frequency.
The cutoff frequency is variable from 1KHz to 20KHz. The passband is flat (Butterworth filter) and has unity gain. The cutoff frequency upper limit is automatically adjusted depending on sample rate (for example, upper limit when used on 22.05KHz sample rate signals is 10KHz).
Visit Jeff Rippe’s website for more information and a link to download HyperFilter.