---
name: "ilowpass"
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/ilowpass"
---

# ilowpass(9)

Low-pass filter with integer inputs and outputs

## NAME

ilowpass - Low-pass filter with integer inputs and outputs

## SYNOPSIS

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

## DESCRIPTION

While it may find other applications, this component was written to create smoother motion while jogging with an MPG.

In a machine with high acceleration, a short jog can behave almost like a step function.  By putting the **ilowpass** component between the MPG encoder **counts** output and the axis jog-counts input, this can be smoothed.

Choose **scale** conservatively so that during a single session there will never be more than about 2e9/**scale** pulses seen on the MPG.  Choose **gain** according to the smoothing level desired.  Divide the axis.*N*.jog-scale values by **scale**.

## FUNCTIONS

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

  Update the output based on the input and parameters.

## PINS

- **ilowpass.*N*.in s32 in**

  - **ilowpass.*N*.out s32 out**

  **out** tracks **in**\***scale** through a low-pass filter of **gain** per period.

## PARAMETERS

- **ilowpass.*N*.scale float rw (default: *1024*)**

  A scale factor applied to the output value of the low-pass filter.

- **ilowpass.*N*.gain float rw (default: *.5*)**

  Together with the period, sets the rate at which the output changes.  Useful range is between 0 and 1, with higher values causing the input value to be tracked more quickly.  For instance, a setting of 0.9 causes the output value to go 90% of the way towards the input value in each period.

## AUTHOR

Jeff Epler

## LICENSE

GPL