# One pole, one zero LP/HP¶

code
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25``` ```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; ```

```what is n? lol...sorry but i mean this seriously! ;)
```
```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 :)
```
```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?
```
```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
```
```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.
```