class:: FOS
summary:: First order filter section.
related:: Classes/SOS
categories::  UGens>Filters>Linear


Description::

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

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


classmethods::

method::ar, kr

argument::in
Signal input.

argument::a0
See formula above.

argument::a1
See formula above.

argument::b1
See formula above.

argument::mul

argument::add

Examples::

code::

(
// 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;
)

::