Houdini 19.0 Nodes Channel nodes Copy

Copy channel node

Produces multiple copies of the second input along the timeline of the first input.

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This CHOP produces multiple copies of the second input along the timeline of the first input. The first input provides the trigger signals or the convolve levels.

The Copy CHOP can be used to produce a motion every time a trigger occurs. It can be used to trigger motion, such as eyelid blinks. The copies it produces can be identical, or the copies can be re-cooked each time a copy is added to the timeline. It is useful for triggering a sound multiple times, where the sounds may overlap in time.

Each copy that is added to the output can be completely different than any other copy. By passing variables through the Variables page, the second (Copy) input can be any chop chain that uses the variables and recooks to create each copy.



Copy Method

Method used for the copy operation.

Triggered Copy

The second input is copied (convolved) over the first input’s trigger points only. A trigger point occurs whenever the first input’s channel crosses the Trigger Threshold value. Overlapping copies are added.


For every sample in the first input’s channel, the second input is shifted to that point in time, scaled by the sample value, and added into the output channels.

Output Method

How to output the channels

One Channel Per Template Channel

Each output channel is a channel from the first input combined with the corresponding channel from the second input.

One Channel Per Copy Channel

Each output channel is a channel from the second input, with copies triggered by every channel of the first input.

Trigger Threshold

The threshold value for triggering copies.


What to do with remaining samples at end of the interval.

Discard Remainder

Output interval = input interval.

Make Output Longer

Output is longer if envelope unfinished.

Mix Remainder to Beginning

Add remainder to samples at the start.

Keep Non-Scoped Channels

If on, non-scoped channels are copied to the output, otherwise they are deleted.


Cook Each Copy

Recook the second input for each triggered copy.

Param 1-10

The parameters are re-calculated for each copy. The first field is the parameter name, the second is its value. You can use local variables and the ic() functions. The parameters you set here are available to any CHOP in the network attached to the second input through function param(“name”, initval), where initval is any initial value for the parameter, usually set to 0.


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.



The current index.


The current channel (0 to NC-1).


The total number of channels.


The value at the current index of the current channel.


The copy number. (The first thing it copies is 0.)


CopyAnimation Example for Copy channel node

This file demonstrates how the Copy CHOP can be used to copy channels and apply them to geometry.

CopyChannels Example for Copy channel node

This example demonstrates how the Copy CHOP additively copies the values of a channel onto the time line of another to create a new channel.

CopyStamping Example for Copy channel node

This example demonstrates how to use the CopyStamp feature of the Copy CHOP. Custom variables are created within the Copy CHOP and used to modify the geometry.

In the file, geometry is imported into CHOPS. The Alpha attribute is scoped and manipulated using the Copy Stamping technique.

The new Alpha data is then brought back to the SOP level, and applied to the geometry’s Position.

See also