---
name: "biquad"
section: "9"
platform: "linux"
package: "linuxcnc-uspace"
version: "1:2.9.4-2+deb13u1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/biquad"
---

# biquad(9)

Biquad IIR filter

## NAME

biquad - Biquad IIR filter

## SYNOPSIS

**loadrt biquad \[count=*N*\|names=*name1*\[,*name2...*\]\]**

## DESCRIPTION

Biquad IIR filter. Implements the following transfer function: H(z) = (n0 + n1z-1 + n2z-2) / (1+ d1z-1 + d2z-2)

## FUNCTIONS

- **biquad.***N* (requires a floating-point thread)

  ## PINS

- **biquad.*N*.in float in**

  Filter input.

- **biquad.*N*.out float out**

  Filter output.

- **biquad.*N*.enable bit in (default: *0*)**

  Filter enable. When false, the **in** pin is passed to the **out** pin without any filtering.  A **transition from false to true** causes filter coefficients to be calculated according to the current **type** and the describing pin and parameter settings

- **biquad.*N*.valid bit out (default: *0*)**

  When false, indicates an error occurred when calculating filter coefficients (require 2\>**Q**\>0.5 and **f0**\>sampleRate/2)

- **biquad.*N*.type u32 in (default: *0*)**

  Filter type determines the type of filter coefficients calculated.  When 0, coefficients must be loaded directly from the **n0,n1,n2,d1** params.  When 1, a low pass filter is created specified by the **f0,Q** pins.  When 2, a notch filter is created specified by the **f0,Q** pins.

- **biquad.*N*.f0 float in (default: *250.0*)**

  The corner frequency of the filter.

- **biquad.*N*.Q float in (default: *0.7071*)**

  The Q of the filter.

- **biquad.*N*.s1 float out (default: *0.0*)**

  1st-delayed internal state (for debug only)

- **biquad.*N*.s2 float out (default: *0.0*)**

  2nd-delayed internal state (for debug only)

## PARAMETERS

- **biquad.*N*.d1 float rw (default: *0.0*)**

  1st-delayed denominator coef

- **biquad.*N*.d2 float rw (default: *0.0*)**

  2nd-delayed denominator coef

- **biquad.*N*.n0 float rw (default: *1.0*)**

  non-delayed numerator coef

- **biquad.*N*.n1 float rw (default: *0.0*)**

  1st-delayed numerator coef

- **biquad.*N*.n2 float rw (default: *0.0*)**

  2nd-delayed numerator coef

## AUTHOR

Peter G. Vavaroutsos

## LICENSE

GPL