A standard first order filter section. Filter coefficients are given directly rather than calculated for you. Formula is equivalent to:

out(i) = (a0 * in(i)) + (a1 * in(i-1)) + (b1 * out(i-1))

### FOS.ar(in: 0, a0: 0, a1: 0, b1: 0, mul: 1, add: 0)

### FOS.kr(in: 0, a0: 0, a1: 0, b1: 0, mul: 1, add: 0)

#### Arguments:

in |
Signal input. |

a0 |
See formula above. |

a1 |
See formula above. |

b1 |
See formula above. |

mul | |

add | |

(
// same as OnePole
{ var x;
x = LFTri.ar(0.4, 0, 0.99);
FOS.ar(LFSaw.ar(200, 0, 0.2), 1 - x.abs, 0.0, x)
}.play;
)
(
// same as OneZero
{ var x;
x = LFTri.ar(0.4, 0, 0.99);
FOS.ar(LFSaw.ar(200, 0, 0.2), 1 - x.abs, x, 0.0)
}.play;
)
(
// same as OnePole, kr
{ var x, ctl;
x = LFTri.kr(0.2, 0, 0.99);
ctl = FOS.kr(LFSaw.kr(8, 0, 0.2), 1 - x.abs, 0.0, x);
LFTri.ar(ctl * 200 + 500);
}.play;
)