Noise channel node

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

All

Parameters

Local variables

Example files

The Noise CHOP makes an irregular wave that never repeats, with values approximately in the range -1 to +1. It appears to have a period like the Wave CHOP, but it is not exact. It generates both smooth curves and noise that is random each sample. It uses the same math as the Noise Texture Operator.

Optionally, an input can be connected. It is assumed that the input contains 1 to 3 channels representing X, Y and Z coordinates of points in space, and are used to sample anywhere in 3D noise space. One index in the input produces one sample in the output.

Optional input: XYZ sample points

Normally the noise is sampled along the X-axis in an XYZ noise space. You can sample anywhere in XYZ.

Parameters

Noise

Type

The noise function used to generate noise.

Sparse	Produces high quality, continuous noise.
Hermite	Produces lower quality noise than Sparse, but quicker.
Harmonic Summation	Sparse noise with the ability to control the frequency step of the harmonics.
Brownian	Produces “Brownian” motion, similar to insect flight.
Random	Every sample is random and unrelated to any other sample. Also know as “white noise” in audio.

Seed

Any number, integer or non-integer. Each number generates completely different noise patterns, but with similar characteristics.

Period

The approximate separation between peaks of a noise cycle, expressed in Units.

Harmonics

The number of higher frequency components to layer on top of the base frequency.

Harmonic Spread

The factor by which the frequency of the harmonics are increased.

Roughness

The amount of the effect of the higher frequency harmonics.

Exponent

Pushes the noise values toward 0, or +1 and -1 (raising the noise to the this power).

Num of Integrals

The number of times to integrate Brownian noise, which affects its smoothness.

Amplitude

The noise’s amplitude.

Constraint

Normalize	Ensures that all noise curves fall between `-1` and `1`.
Constraint	Allows the noise curve to start and/or end at selected values. The average value may also be constrained.
Starting Value	The value noise curves should start at.
Ending Value	THe value noise curves should end at.
Mean Value	The mean value noise curves should have.

Channel

Channel Name	The names of the channels to be created.
Start	The start of the channels.
End	The end of the channels.
Sample Rate	The sample rate of the channels.
Extend Left	The left extend conditions of the channels.
Extend Right	The right extend conditions of the channels.
Default Value	The default value for extend conditions.

Common

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

Scope

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:

`chan2`	Matches a single channel name.
`chan3 tx ty tz`	Matches four channel names, separated by spaces.
`chan*`	Matches each channel that starts with `chan`.
`foot`	Matches each channel that has `foot` in it.
`t?`	The `?` matches a single character. `t?` matches two-character channels starting with t.
`r[xyz]`	Matches channels `rx`, `ry` and `rz`.
`blend[3-7:2]`	Matches number ranges giving `blend3`, `blend5`, and `blend7`.
`blend[2-3,5,13]`	Matches channels `blend2`, `blend3`, `blend5`, `blend13`.
`t[xyz]`	`[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.

Units

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).

Note

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.

Unload

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.

Note

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.

Local variables

I	The current index.
C	The current channel (0 to NC-1).
NC	The total number of channels.
S,E	The start and end indices of the noise curve.

Example files

NoiseBasic

$HFS/houdini/help/examples/nodes/chop/noise/NoiseBasic.cmd

Load | Launch

This example demonstrates the Noise CHOP.

The Noise CHOP makes an irregular wave that never repeats, with values approximately in the range -1 to +1. Or using the “Time Slice” option a single noise value can be returned.

Usages in other examples

Example name	Example for
CopyStamping	Copy channel node	Load \| Launch
Constant02	Constant channel node	Load \| Launch
ChannelBasic	Channel channel node	Load \| Launch
Envelope	Envelope channel node	Load \| Launch
Blend	Blend channel node	Load \| Launch
ChannelSOPColorExample	Channel surface node	Load \| Launch