One pole, one zero LP/HP

References : Posted by mistert[AT]inwind[DOT]it
Code :
void SetLPF(float fCut, float fSampling)
{
    float w = 2.0 * fSampling;
    float Norm;

    fCut *= 2.0F * PI;
    Norm = 1.0 / (fCut + w);
    b1 = (w - fCut) * Norm;
    a0 = a1 = fCut * Norm;
}

void SetHPF(float fCut, float fSampling)
{
    float w = 2.0 * fSampling;
    float Norm;

    fCut *= 2.0F * PI;
    Norm = 1.0 / (fCut + w);
    a0 = w * Norm;
    a1 = -a0;
    b1 = (w - fCut) * Norm;
}

Where
out[n] = in[n]*a0 + in[n-1]*a1 + out[n-1]*b1;

Comments
from : petersteiner[AT]hypemart[DOT]net
comment : what is n? lol...sorry but i mean this seriously! ;)

from : musicdsp[AT]dsparsons[DOT]co[DOT]uk
comment : n is the index of sample being considered. out[] is an array of samples being output, and in[] is the input array. you would construct a loop such that: [Pseudocode] loop n{0..numsamples-1} out[n] = in[n]*a0 + in[n-1]*a1 + out[n-1]*b1; end loop; [/Pseudocode] You will need some cleverness so that [n-1] doesn't cause an index error when n=0, but I'll leave that to you :)

from : petersteiner[AT]hypemart[DOT]net
comment : whoops - sorry, of course n = number... stupid me ;) interesting code, i will see if can adapt that to delphi, shouldn´t be a big deal :) i assume i dont need to place either setHPF or LPF into the samples loop, just the block itself?

from : musicdsp[AT]dsparsons[DOT]co[DOT]uk
comment : absolutey - set the coefficients outside of the loop. There is the case of changes being made whilst the loop is running, depends what platform/host you are writing for. I'm a delphi code as well. Feel free to use my posted address if you need to :) DSP

from : rouncer81[AT]hotmail[DOT]com
comment : implemented first try worked. excellent for what it is.

from : jenaleek[ AT ]yahoo[ DOT ]com
comment : Shouldn't that be float w = 2*PI*fSampling; ??? In which case we can simplify: void SetLPF(float fCut, float fSampling) { a0 = fCut/(fSampling+fCut); a1 = a0; b1 = (fSampling-fCut)/(fSampling+fCut); } void SetHPF(float fCut, float fSampling) { a0 = fSampling/(fSampling+fCut); a1 = -a0; b1 = (fSampling-fCut)/(fSampling+fCut); } You can keep the norm = 1/(fSampling+fCut) if you like.