Houdini 19.0 Nodes Channel nodes Constant

Constant channel node

Create up to forty new channels.

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This chop allows you to create up to forty new channels. Each channel can be named and assigned a different value. To create a channel, enter a channel name in any left parameter in the 0, 10, 20 or 30 pages, then adjust the value to its right.

The interval is one sample by default (at index 0). An interval range can be optionally set in the Channel tab.

A simple Constant CHOP with no inputs is the most common use of the chop. However, the channels names and values can be set up by connecting any CHOP to its input and clicking the Snapshot Input button on the Snap tab. This allows you to get some channels from another chop and adjust them with sliders in the Constant CHOP.

The second input can be used to add offsets to the constant values. When the second input (Active) is greater than zero, any change to the first input will be added to the output of the CHOP. This is useful for adjusting Constant CHOP values from external input devices like a midi slider box. For example you can connect the mouse or a midi slider box to a Mouse or midi In CHOPs, and you can raise/lower the Constant CHOP values by holding the Active input on, while moving the mouse or sliders.



Channel 0-9

User-defined channels 0 to 9.


Channel 10-19

User-defined channels 10 to 19.


Channel 20-29

User-defined channels 20 to 29.


Channel 30-39

User-defined channels 30 to 39.


Snapshot Input

Click this button to capture the input channels' values at the current frame.

First Channel

Specify the starting channel index to snap from.

Active Needs Current

When on, the second input, the Active input only has an effect if this CHOP is the current CHOP. When off, it doesn’t matter if this is the current CHOP. Used by the Animation Editor when editing keyframes.


Single Frame

Only create one-sample channels, at the Start position.


The start position of the CHOP.


The end position of the CHOP.

Sample Rate

The sample rate of the CHOP.

Extend Left

The left extend condition (before the CHOP’s start).

Extend Right

The right extend condition (after the CHOP’s end).

Default Value

The value to use for the “Default Value” extend condition type.


Some of these parameters may not be available on all CHOP nodes.


To determine which channels get affected, some CHOPs have a scope string. Patterns can be used in the scope, for example * (match all), and ? (match single character).

The following are examples of possible channel name matching options:


Matches a single channel name.

chan3 tx ty tz

Matches four channel names, separated by spaces.


Matches each channel that starts with chan.


The ? matches a single character. t? matches two-character channels starting with t.


Matches channels rx, ry and rz.


Matches number ranges giving blend3, blend5, and blend7.


Matches channels blend2, blend3, blend5, blend13.


[xyz]matches three characters, giving channels tx, ty and tz.

Sample Rate Match

The Sample Rate Match Options handle cases where multiple input CHOPs’ sample rates are different.

Resample At First Input’s Rate

Use rate of first input to resample others.

Resample At Maximum Rate

Resample to highest sample rate.

Resample At Minimum Rate

Resample to the lowest sample rate.

Error if Rates Differ

Does not accept conflicting sample rates.


The units for which time parameters are specified.

For example, you can specify the amount of time a lag should last for in seconds (default), frames (at the Houdini FPS), or samples (in the CHOP’s sample rate).


When you change the Units parameter, it does not convert the existing parameters to the new units.

Time Slice

Time Slicing is a feature which boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel does need to be evaluated every frame, then cooking the entire range of the channel is unnecessary. It is more efficient to calculate only the fraction of the channel that is needed. This fraction is known as a Time Slice.


Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.

Export Prefix

The Export prefix is prepended to CHOP channel names to determine where to export to.

For example, if the CHOP channel was named geo1:tx, and the prefix was /obj, the channel would be exported to /obj/geo1/tx.


You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as obj:geo1:tx.

Graph Color

Every CHOP has this option. Each CHOP gets a default color assigned for display in the Graph port, but you can override the color in the Common page under Graph Color. There are 36 RGB color combinations in the Palette.

Graph Color Step

When the graph displays the animation curves and a CHOP has two or more channels, this defines the difference in color from one channel to the next, giving a rainbow spectrum of colors.


Constant01 Example for Constant channel node

This example demonstrates the most common use of the Constant CHOP by creating channels which have one unchanging value.

Constant02 Example for Constant channel node

This example demonstrates how the Constant CHOP can import channels through the first input by adopting their names and values at the current frame.

See also