**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.