ANTIALIAS - Butterworth anti-aliasing filter
antialias use before increasing the sampling interval of data
i.e. subsampling
Function Prototype:
void antialias (float frac, int phase, int n, float p[], float q[]);
Input:
frac current sampling interval / future interval (should be <= 1)
phase =0 for zero-phase filter; =1 for minimum-phase filter
n number of samples
p array[n] of input samples
Output:
q array[n] of output (anti-alias filtered) samples
Notes:
The anti-alias filter is a recursive (Butterworth) filter. For zero-phase
anti-alias filtering, the recursive filter is applied forwards and backwards.
Author: Dave Hale, Colorado School of Mines, 06/06/90