musicdsp.org source code archive - WSInf

One pole LP and HP (click this to go back to the index)
References : Posted by Bram
Code :
LP:
recursion: tmp = (1-p)*in + p*tmp with output = tmp
coefficient: p = (2-cos(x)) - sqrt((2-cos(x))^2 - 1) with x = 2*pi*cutoff/samplerate
coeficient approximation: p = (1 - 2*cutoff/samplerate)^2
HP:
recursion: tmp = (p-1)*in - p*tmp with output = tmp
coefficient: p = (2+cos(x)) - sqrt((2+cos(x))^2 - 1) with x = 2*pi*cutoff/samplerate
coeficient approximation: p = (2*cutoff/samplerate)^2
Comments
from : skyphos_atw@hotmail.com
comment : coefficient: p = (2-cos(x)) - sqrt((2-cos(x))^2 - 1) with x = 2*pi*cutoff/samplerate
p is always -1 using the formula above. The square eliminates the squareroot and (2-cos(x)) - (2-cos(x)) is 0.
from : q@q
comment : Look again. The -1 is inside the sqrt.