Houdini 17.5 Nodes Channel nodes

Wave channel node

Creates a waveform that is repeated.

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This CHOP produces a variety of waveforms. On top of the actual waveform, an offset, decay and ramp can be applied.

Multiple channels can be generated by using patterns in the Channel Name parameter. A few examples of name pattern generation:

tx ty tz             tx ty tz
t[xyz]               tx ty tz
chan[1-4]            chan1 chan2 chan3 chan4
c[xyz][1-3:2,15]     cx1 cy1 cz1 cx3 cy3 cz3 cx15 cy15 cz15

These parameters are applied in the following order: Offset, Amplitude, Decay, Ramp, and Expression.




The wave type which is one of the following:


A constant valued "wave".


A sine wave.


A Gaussian wave (also known as bell or normal curve).


A triangular sawtooth wave.


A square wave.


A periodic one-sample pulse wave.


A user defined non-periodic expression.


The period of the wave.


The phase of the wave, from 0 to 1.


The bias of the waveform. Only Gaussian, triangle and square waves have biases.


The value offset of the waveform.


The amplitude of the waveform.

Decay Rate

The decay rate of the waveform, represented as the fraction of decay after 1 Unit of time (default is one second)

Ramp Slope

A ramp is added the wave: amount per Unit of time.


Expression to use for "Expression" Type.


Channel Name

The names of the channels to create. Patterns like chan[1-20] generate multiple channels.

Channel Range

Indicates how much of the channel to cook.

Use Full Animation Range

All of the current global animation range.

Use Current Frame

Only the sample at the current frame.

Use Start/End

Specify the range using the Start/End parameters.

Start, End

The start time of the channels.

Sample Rate

The sample rate of the channels.

Extend Left

The left extend conditions.

Extend Right

The right extend conditions.

Default Value

The default value for extend conditions.


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.


Matches each channel that has foot in it.


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 loop index, which is reset every period.


The current period count, starting at zero.


The current channel (0 to NC-1).


The total number of channels.


The period of the wave (from the Period parameter).


The phase of the wave (from the Phase parameter).


The bias of the wave (from the Bias parameter).


WaveGrid Example for Wave channel node

This example demonstrates how to warp geometry using a Wave CHOP.

The following examples include this node.

Area with one input Example for Area channel node

This example demonstrates the Area CHOP used with one input.

A Wave CHOP is used as a first input source channel for the Area CHOP.

Area with two inputs Example for Area channel node

This is a demonstration of the Area CHOP using two inputs, where a single Wave CHOP is input into the first and second inputs of the Area CHOP.

Area with three inputs Example for Area channel node

This example contains a demonstration of the Area CHOP using all three inputs.

A single Wave CHOP is used in the first and second input as a source and as a range modifier. Then another Wave CHOP is used in the third input to modify the length of the output channel of the Area CHOP.

Blend Example for Blend channel node

This example demonstrates how the Blend CHOP combines several channels together using an interpolated blend weight control.

BlendLimit Example for Composite channel node

You can chain the Composite CHOP together to take two or more channels and do an ordered sequence blend. The Composite CHOP takes a control curve and uses it to determine which channel to use with each Composite CHOP working on two channels at a time, creating a sequence blend. The first Composite node processes the first and second channel, the second Composite node processes the result from the first node and the third channel, and so on.

A key component of this network is the Limit CHOP. It processes the control curve so the range is valid for the pair of channels being processed by the associated Composite node.

Composite Example for Composite channel node

This example demonstrates how the Composite CHOP blends channels together where the first input is the base channel and the second input is the layer channel.

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.

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.

Cycle Example for Cycle channel node

This example demonstrates how the Cycle CHOP seamlessly loops input channels. The Cycle is customized by setting the amount of repetitions before and after the input channel, and by setting up the orientation.

Delay Example for Delay channel node

This example demonstrates how the Delay CHOP copies and layers input channels. The Delay (timing) and Gain (Scale) values of each copy are added together to output a single channel.

Envelope Example for Envelope channel node

This example illustrates how the Envelope CHOP outputs the maximum amplitude of a channel in the vicinity of each sample of the input. Here, envelope1 and envelope2 try to follow the maximum amplitude of the noisy curve they use as input.

To visualize the channels in this demonstration, please enter the CHOP network and use the default CHOPs desktop.

Export Example for Export channel node

This is an example of the Export CHOP. The Export CHOP is a convenient tool for exporting channels. It allows you to match a CHOP’s channels with different destination channels, without needing to rename the channels. This demonstrates a method to export channels from CHOPs to the ty parameter of a model.

Extend Example for Extend channel node

This is an example of how the Extend CHOP determines the values that are computed when sampling outside the interval.

feedbackloop Example for Feedback channel node

In this example, we demonstrate how a feedback node can be used to get the state of a CHOP as it was one frame or time slice ago.

LagBasic Example for Lag channel node

This file demonstrates the Lag CHOP.

The Lag CHOP can apply a lag, or overshoot an input channel. It can also limit the velocity and acceleration of input channels. The result of modifying channels in this way is similar to the effect of the Spring CHOP, yet not as naturalistic.

LimitBasic Example for Limit channel node

This example file uses the Limit CHOP both to limit the height and to "quantize" the values of a channel.

By limiting the height the Limit CHOP can keep data values from going to high or from falling to low. To "quantize" the data, the curve is broken into steps rather than a smooth curve.

MathBasic Example for Math channel node

These examples demonstrate the ability of the Math CHOP to combine multiple channels together.

The first example shows two different methods of controlling the amplitude of a sine wave. The second example shows three different channels combined into one.

MergeBasic Example for Merge channel node

This example file demonstrates the Merge CHOP.

Two CHOPs are read in with the Merge CHOP and then combined in a variety of different ways. The curves can either be stretched or cut off depending on the chosen settings.

Rename Example for Rename channel node

The Rename CHOP renames the channel names in a CHOP.

To visualize the channels in this demonstration, please enter the CHOP network.

For a complete list of the types of renaming possible, please see the Houdini documentation.

Sequence Example for Sequence channel node

The Sequence CHOP is used to combine multiple waves into a single wave.

This CHOP takes all its input CHOPs and appends one wave after another. It is expected the input CHOPs all have the same channels.

The end section of the first CHOP is overlapped with the start section of the second CHOP, and so on for the rest of the input CHOPs. The second input is shifted to line up with the end of the first.

To visualize the channels in this demonstration, please enter the CHOP network.

Shift Example for Shift channel node

This example demonstrates how the Shift CHOP changes the interval of a CHOP wave, keeping its content and length the same.

The Reference parameter chooses whether the Start or the End is being redefined.

The Unit Values parameter sets whether the new Start/End frame is Relative to its original position, or an Absolute frame number.

Slope Example for Slope channel node

This example demonstrates how the Slope CHOP calculates the slope (or derivative) of the input channels.

If the input CHOP represents position, the slope can be interpreted as speed.

By default, the Slope CHOP converts position to speed.

Stretch Example for Stretch channel node

This example demonstrates how the Stretch CHOP changes the Start and/or End interval. It then resamples the input channel, preserving the shape of the channel. The sample rate remains the same, however, the interval changes.

WaveGrid Example for Wave channel node

This example demonstrates how to warp geometry using a Wave CHOP.

DensityViscosity Example for FLIP Solver dynamics node

This example demonstrates two fluids with different densities and viscosities interacting with a solid object.

ChannelSOPColorExample Example for Channel geometry node

This example demonstrates using CHOPs to drive geometry color values via the Channel SOP.

See also

Channel nodes

  • Acoustic

    Design audio filters and sound materials for the spatial audio system.

  • Agent

    Imports an animation clip from an agent primitive.

  • Area

    Calculates the area under a channel’s graph, which is the same as calculating the integral of a channel, or integrating the channel.

  • Attribute

    Adds, removes or updates attributes of the input chop.

  • Audio In

    Receives audio input from the analog audio ports or the digital port.

  • Band EQ

    A 14-band equalizer which filters audio input channels in the same way that a conventional band equalizer uses a bank of sliders to filter fixed-frequency bands of sound.

  • Beat

    Manually tap the beat of a piece of music, and automatically generate a repeating ramp or pulse that continues to keep time with the music after the taps stop.

  • Blend

    Combines two or more chops in input 2, 3 and so on, by using a set of blending channels in input 1.

  • BlendPose

    Performs multi-dimensional, example-based interpolation of channels.

  • Channel

    Creates channels from the value of its parameters.

  • Channel VOP

    Contains a VOP network that can manipulate channel data.

  • Channel Wrangle

    Runs a VEX snippet to modify channel data.

  • Composite

    Layers (blends) the channels of one CHOP on the channels of another CHOP.

  • Constant

    Create up to forty new channels.

  • Constraint Blend

    Combines two or more chops by using a list of weights specified as parameters.

  • Constraint Get Local Space

    Returns an Object Local Transform.

  • Constraint Get Parent Space

    Returns an Object Parent Transform.

  • Constraint Get World Space

    Returns an Object World Transform.

  • Constraint Lookat

    Constrains rotation so it always points toward a target position.

  • Constraint Object

    Compares two objects and returns information on their relative positions and orientations.

  • Constraint Object Offset

    Compares two objects and returns information on their relative positions and orientations.

  • Constraint Object Pretransform

    Returns an Object Pretransform.

  • Constraint Offset

    Applies an transformation offset after evaluating a constraint.

  • Constraint Parent

    Reparent an object.

  • Constraint Path

    Position an object on a path and orient it to the path’s direction.

  • Constraint Points

    Position and Orient an object using point positions from a geometry.

  • Constraint Sequence

    Combines multiple chops by blending the inputs in sequence.

  • Constraint Simple Blend

    Combines two chops by using a single weight specified as a parameter.

  • Constraint Surface

    Position and Orient an object using the surface of a geometry.

  • Constraint Transform

    Takes translate, rotate, and/or scale channels and transforms them.

  • Copy

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

  • Count

    Counts the number of times a channel crosses a trigger or release threshold.

  • Cycle

    Creates cycles.

  • Delay

    Delays the input, and can be run in normal or time-sliced mode.

  • Delete

    Removes channels coming from its input.

  • Device Transform

    Turns data from device inputs into transform data

  • Dynamics

    Extracts any information from a DOP simulation that is accessible through the dopfield expression function.

  • Envelope

    Outputs the maximum amplitude in the vicinity of each sample of the input.

  • Euler Rotation Filter

    Fixes discontinuity of rotation data after cracking matrices

  • Export

    A convenient tool for exporting channels.

  • Export Constraints

    Export Constraints Network on any object

  • Expression

    Modify input channels by using expressions.

  • Extend

    Only sets the "extend conditions" of a chop, which determines what values you get when sampling the CHOP before or after its interval.

  • Extract Bone Transforms

    Extracts the current world or local space bone transforms from a geometry object.

  • Extract Locomotion

    Extracts locomotion from an animation clip.

  • Extract Pose-Drivers

    Creates channels from the specified derived transforms, node parameters and CHOP channels for pose-space deformation.

  • FBX

    Reads in channel data from an FBX file.

  • Fan

    Used for controlling other CHOPs.

  • Feedback

    Get the state of a chop as it was one frame or time slice ago.

  • Fetch Channels

    Imports channels from other CHOPs.

  • Fetch Parameters

    Imports channels from other OPs.

  • File

    Reads in channel and audio files for use by chops.

  • Filter

    Smooths or sharpens the input channels.

  • Foot Plant

    Computes when position channels are stationary.

  • Foreach

    Divides the input channels into groups, cooking the contained network for each group.

  • Function

    Provides more complicated math functions than found in the Math CHOP such as trigonometic functions, logarithmic functions, and exponential functions.

  • Gamepad

    Turns input values for the gamepad or joystick device into channel outputs.

  • Geometry

    Uses a geometry object to choose a sop from which the channels will be created.

  • Gesture

  • Handle

    The "engine" which drives Inverse Kinematic solutions using the Handle object.

  • Hold

    Sample and hold the value of the first input.

  • IKSolver

    Solves inverse kinematics rotations for bone chains.

  • Identity

    Returns an identity transform.

  • Image

    Converts rows and/or columns of pixels in an image to CHOP channels.

  • Interpolate

    Treats its multiple-inputs as keyframes and interpolates between them.

  • InverseKin

    Generates channels for bone objects based on a bone chain and an end affector.

  • Invert

    Returns an invert transform of the input.

  • Jiggle

    Creates a jiggling effect in the translate channels passed in.

  • Keyboard

    Turns key presses into channel output.

  • Lag

    Adds lag and overshoot to channels.

  • Layer

    Mix weighted layers of keyframed animation from multiple Channel CHOPs to a base Channel CHOP.

  • Limit

    Provides a variety of functions to limit and quantize the input channels.

  • Logic

    Converts channels of all its input chops into binary channels and combines them using a variety of logic operations.

  • Lookup

    Uses a channel in the first input to index into a lookup table in the second input, and output values from the lookup table.

  • MIDI In

    The MIDI In CHOP reads Note events, Controller events, Program Change events, and Timing events from both midi devices and files.

  • MIDI Out

    The MIDI Out CHOP sends MIDI events to any available MIDI devices.

  • Math

    Perform a variety of arithmetic operations on and between channels.

  • Merge

    Takes multiple inputs and merges them into the output.

  • Mouse

    Outputs X and Y screen values for the mouse device.

  • Mouse 3D

    Turns input values for the Connexion space mouse into channel outputs.

  • Multiply

    Post multiplies all the input transformations.

  • Network

    Similar to the Pipe In/Out CHOPs in Network mode.

  • Noise

    Makes an irregular wave that never repeats, with values approximately in the range -1 to +1.

  • Null

    Used as a place-holder and does not have a function of its own.

  • Object

    Compares two objects and returns information on their relative positions and orientations.

  • ObjectChain

    Creates channels representing the transforms for a chain of objects.

  • Oscillator

    Generates sounds in two ways.

  • Output

    Marks the output of a sub-network.

  • Parametric EQ

    Filters an audio clip, and then applies other audio effects.

  • Particle

    Produces translate and rotate channels to move Objects according to the positions of particles in a POP Network.

  • Pass Filter

    Filters audio input using one of four different filter types.

  • Phoneme

    Translates english text into a series of phonetic values.

  • Pipe In

    Pipes data from custom devices into a CHOP, without needing the Houdini Developers' Kit or knowledge of Houdini internals.

  • Pipe Out

    Transmit data out of Houdini to other processes.

  • Pitch

    Attempts to extract the fundamental pitch of a musical tone from the input audio.

  • Pose

    Store a transform pose for later use by evaluating the input.

  • Pose Difference

    Computes the difference between two poses.

  • Pretransform

    Takes translate, rotate, and/or scale channels and transforms them using the pretransform of the given object.

  • Pulse

    Generates pulses at regular intervals of one channel.

  • ROP Channel Output

  • Record

  • Rename

    Renames channels.

  • Reorder

    Reorders the first input CHOP’s channels by numeric or alphabetic patterns.

  • Resample

    Resamples an input’s channels to a new rate and/or start/end interval.

  • Sequence

    Takes all its inputs and appends one chop after another.

  • Shift

    This time-shifts a CHOP, changing the start and end of the CHOP’s interval.

  • Shuffle

    Reorganizes a list of channels.

  • Slope

    Calculates the slope (or derivative) of the input channels.

  • Spatial Audio

    The rendering engine for producing 3D audio.

  • Spectrum

    Calculates the frequency spectrum of the input channels, or a portion of the channels.

  • Spline

    Edit the channel data by using direct manipulation of cubic or Bezier handles in the graph of the CHOP.

  • Spring

    Creates vibrations influenced by the input channels, as if a mass was attached to a spring.

  • Stash

    Caches the input motion in the node on command, and then uses it as the node’s output.

  • Stash Pose

    Stashes the bone transforms and pose-drivers for use by the Pose-Space Deform SOP and Pose-Space Edit SOP nodes.

  • Stretch

    Preserves the shape of channels and the sampling rate, but resamples the channels into a new interval.

  • Subnetwork

    Allows for the simplification of complex networks by collapsing several CHOPs into one.

  • Switch

    Control the flow of channels through a CHOPnet.

  • Time Range

    This converts an input node in Current Frame mode to a Time Range mode by re-cooking it multiple times.

  • Time Shift

    This time-shifts a CHOP, re-cooking the node using different time.

  • Transform

    Takes translate, rotate, and/or scale channels and transforms them.

  • TransformChain

    Combines a chain of translate, rotate, and/or scale channels.

  • Trigger

    Adds an audio-style attack/decay/sustain/release (ADSR) envelope to all trigger points in the input channels.

  • Trim

    Shortens or lengthens the input’s channels.

  • VEX Waveform

    This function is a sub-set of the waveform CHOP.

  • Vector

    Performs vector operations on a set or sets of channels.

  • Voice Split

    The Voice Split CHOP takes an audio track and separates "words" out into different channels.

  • Voice Sync

    The Voice Sync CHOP detects phonemes in an audio channel given some audio phoneme samples and pro…

  • Warp

    Time-warps the channels of the first input (the Pre-Warp Channels) using one warping channel in the second input.

  • Wave

    Creates a waveform that is repeated.