Houdini 19.0 Nodes Channel nodes Pulse

Pulse channel node

Generates pulses at regular intervals of one channel.

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This CHOP generates pulses at regular intervals of one channel. The amplitude of each pulse can be edited with the chop sliders or with handles on the graph.

The Pulse chop can be used as triggers to the Copy CHOP, and can represent regularly-timed events.

By default, the pulses are a single sample long, but you can increase the Pulse Width so that the pulses are steps to the next pulse. You can also interpolate the values between pulses, as Linear, Ease In Ease Out, Cubic or other curves.

The pulses can be restricted to a minimum / maximum limit. If the Limit Type is Clamp, the graph has additional convenient handles at the minimum and maximum for each pulse.

The Pulse CHOP generates a single channel of up to 32 pulses, and you can merge several Pulse chops into a multi-channel CHOP.

The Pulse CHOP uses its optional second input as a start/end reference, so a number of Pulse chops can be stretched to the same interval.

In order to set the value at the last sample, the option, Last Pulse at Last Sample is provided. Otherwise, the last pulse is prior to the last sample.



Number of Pulses

Total number of pulses in the channel.


How to interpolate between pulse values.

Pulse Width

The width of each pulse, in Units.

Limit Type

Pulse values can be clamped into a range given by the minimum and maximum parameters listed below.


The minimum pulse value.


The maximum pulse value.

Last Pulse at Last Sample

If on, the last sample will contain the last pulse, with pulses at the start of intervals of length “Channel Length / (#Pulses -1)”. Otherwise the pulses will be at the start of intervals of length “Channel Length / #Pulses”.

0, 8, 16, 24

Pulse x

The value of each pulse.



The start time of the desired interval.


The end time of the desired interval.

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.


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 channel (0 to NC-1).


The total number of channels.

See also