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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 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.
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
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 available on all CHOP nodes.
Scope
To determine the channels that are affected, some CHOPs have a scope string. Patterns can be used in 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.
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 the rate of the first input to resample the others.
Resample At Maximum Rate
Resample to the 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 of the time parameters.
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, the existing parameters are not converted to the new units.
Time Slice
Time slicing is a feature that boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel needs 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 the 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 to it for display in the graph, but you can override the color with the 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.
Locals ¶
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.
Examples ¶
NoiseBasic Example for Noise channel node
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.
NoiseTransform Example for Noise channel node
This example demonstrates using the Noise CHOP to generate animation and apply it to geometry.