Noise CHOP
Summary
The Noise CHOP makes an irregular wave that never repeats, with values approximately in the range 1 to +1.
It generates both smooth curves and noise that is random each sample. It uses the same math as the Noise SOP.
You can create several curves with different shapes, and you can adjust period, amplitude, harmonics and more.
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.
All noise functions work identically with Time Slicing on and off, with the exception of Harmonic Summation and Brownian whose methods cannot be limited to 1 in Time Slice mode. When the Timeline wraps around to frame 1, the noise functions will continue uninterrupted.
Parameters  Noise Page
Type type
 ⊞  The noise function used to generate noise. The functions available are:
 Sparse
sparse
 Produces high quality, continuous noise based on Sparse Convolution.
 Hermite
hermite
 Quicker than Sparse, but produces lower quality noise.
 Harmomic Summation
harmonic
 Sparse noise with the ability to control the frequency step of the harmonics. Slowest type.
 Brownian
brownian
 Works like a bug in random flight. With Num of Integrals at 2, its acceleration is changed randomly every frame.
 Random
random
 (White Noise) Every sample is random and unrelated to any other sample. It is the same as "white noise" in audio.
 Alligator
alligator
 Cell Noise.
Seed seed
 Any number, integer or noninteger, which starts the random number generator. Each number gives completely different noise patterns, but with similar characteristics.
Period period
 The approximate separation between peaks of a noise cycle. It is expressed in Units. Increasing the period stretches the noise pattern out.
Period is the opposite of frequency. If the period is 2 seconds, the base frequency is 0.5 cycles per second, or 0.5Hz for short. Hz refers to Hertz, the electrical and audio engineer of the 19th century, not the car guy.
If the Type is set to Random, setting this to zero will produce completely random noise. Otherwise, the period should be greater than zero.
Period Unit periodunit
 Select the units to use for this parameter, Samples, Frames, Seconds, or Fraction.
Harmonics harmon
 The number of higher frequency components to layer on top of the base frequency. The higher this number, the bumpier the noise will be (as long as roughness is not set to zero). 0 harmonics give the base shape.
Harmonics with a base frequency of 0.1Hz will by default produce harmonics at 0.2Hz, 0.4Hz, 0.8Hz, etc. (up to the number of harmonics specified by the Harmonics parameter).
Harmonic Spread spread
 The factor by which the frequency of the harmonics are increased. It is normally 2. A spread of 3 and a base frequency of 0.1Hz will produce harmonics at 0.3Hz, 0.9Hz, 2.7Hz, etc. This parameter is only valid for the Harmonic Summation type.
Roughness rough
 Controls the effect of the higher frequency noise. When roughness is zero, all harmonics above the base frequency have no effect. At one, all harmonics are equal in amplitude to the base frequency. When roughness is between one and zero, the amplitude of higher harmonics drops off exponentially from the base frequency.
The default roughness is 0.5. This means the amplitude of the first harmonic is 0.5 of the base frequency, the second is 0.25, the third is 0.125. The harmonics are added to the base to give the final shape. The Harmonics parameter and the Roughness parameter must both be nonzero to see the harmonic effects.
Exponent exp
 Pushes the noise values toward 0, or +1 and 1. (It raises the value to the power of the exponent.) Exponents greater than one will pull the channel toward zero, and powers less than one will pull peaks towards +1 and 1. It is used to reshape the channels.
Num of Integrals numint
 Defines the number of times to integrate (see the Area CHOP p. 114) the Brownian noise. Higher values produce smoother curves with fewer features. Values beyond 4 produce somewhat identical curves. This parameter is only valid for the Random noise type.
Amplitude amp
 Defines the noise value's amplitude (a scale on the values output).
Reset reset
 Only available if operator's Time Slice
Parameter is on. Toggling this parameter will reset the noise calculation and hold the value until the parameter is released again.
Reset Pulse resetpulse
 Only available if operator's Time Slice
Parameter is on. Pulsing this parameter will reset the noise calculation.
Parameters  Transform Page
The Translate, Rotate, Scale and Pivot parameters let you sample in a different part of the 3D noise space. Imagine a different noise value for every XYZ point in space. Normally, the Noise CHOP samples the noise space from (0,0,0) along the Xaxis in steps of 2/period. /tx /ty /tz /rx /ry /rx /sx /sy /sz /px /py /pz
 By changing the transform, you are translating, rotating and scaling the line along which the Noise CHOPs samples the noise space. A slight Yrotation is like walking in a straight path in the mountains, recording your altitude along the way, then restarting from the same initial location, walking in a slightly different direction. Your altitude starts off being similar but then diverges.
Transform Order xord
 ⊞  Changing the Transform Order will change where things go much the same way as going a block and turning east gets you to a different place than turning east and then going a block. In matrix math terms, if we use the 'multiply vector on the right' (column vector) convention, a transform order of Scale, Rotate, Translate would be written as T * R * S * Position
 Scale Rotate Translate
srt

 Scale Translate Rotate
str

 Rotate Scale Translate
rst

 Rotate Translate Scale
rts

 Translate Scale Rotate
tsr

 Translate Rotate Scale
trs

Rotate Order rord
 ⊞  As with transform order (above), changing the order in which the rotations take place will alter the final position and orientation. A Rotation order of Rx Ry Rz would create the final rotation matrix as follows R = Rz * Ry * Rx
 Rx Ry Rz
xyz

 Rx Rz Ry
xzy

 Ry Rx Rz
yxz

 Ry Rz Rx
yzx

 Rz Rx Ry
zxy

 Rz Ry Rx
zyx

Translate t
 ⊞  XYZ translation values.
 X
tx

 Y
ty

 Z
tz

Rotate r
 ⊞  XYZ rotation, in degrees.
 X
rx

 Y
ry

 Z
rz

Scale s
 ⊞  XYZ scale to shrink or enlarge the transform.
 X
sx

 Y
sy

 Z
sz

Pivot p
 ⊞  XYZ pivot to apply the above operations around.
 X
px

 Y
py

 Z
pz

Parameters  Constraints Page
Constraint constraint
 ⊞  Constraint and its parameters allows the noise curve to start and/or end at selected values. The mean value may also be enforced. Note: This only works when Time Slice is Off because time slicing has no predetermined start/end.
 None
none
 No constraints set.
 Start Value
start
 Sets the noise starting position to the value set in 'Starting Value' parameter below.
 End Value
end
 Sets the noise ending position to the value set in 'Ending Value' parameter below.
 Mean Value
offset
 Sets the noise mean position to the value set in the 'Mean Value' parameter below.
 Start/End Values
endpoints
 Set the starting and ending position of the noise separately using the parameters below.
Starting Value constrstart
 Value for the starting position.
Ending Value constrend
 Value for the ending position.
Mean Value constrmean
 Value for the mean value of the noise.
Normalize normal
 Ensures that all noise curves fall between 1 and 1. Applied before the Amplitude parameter. Only valid for Random and Harmonic Summation noise types, since Hermite and Sparse noise are always normalized. Normalizing random noise occurs between integrations, producing a more controlled curve. Note: This only works when Time Slice is Off because time slicing has no predetermined start/end.
Parameters  Channel Page
Channel Names channelname
 You can creates many channels with simple patterns like "chan[120]
", which generates 20 channels from chan1 to chan20. See the section, Common CHOP Parameters for a description of this and all Options. See Scope and Channel Name Matching Options. Each channel has a unique seed, so all channels will be different with the same parameter settings.
Start start
 Start of the interval, expressed in Units (seconds, frames or samples).
Start Unit startunit
 Select the units to use for this parameter, Samples, Frames, or Seconds.
End end
 End of the interval, expressed in Units (seconds, frames or samples).
End Unit endunit
 Select the units to use for this parameter, Samples, Frames, or Seconds.
Sample Rate rate
 The sample rate of the channels, in samples per second. Default: me.time.rate
Extend Left left
 ⊞  The left extend conditions (before/after range).
 Hold
hold
 Hold the current value of the channel.
 Slope
slope
 Continue the slope before the start of the channel.
 Cycle
cycle
 Cycle the channel repeatedly.
 Mirror
mirror
 Cycle the channel repeatedly, mirroring every other cycle.
 Default Value
default
 Use the constant value specified in the Default Value parameter.
Extend Right right
 ⊞  The right extend conditions (before/after range).
 Hold
hold
 Hold the current value of the channel.
 Slope
slope
 Continue the slope after the end of the channel.
 Cycle
cycle
 Cycle the channel repeatedly.
 Mirror
mirror
 Cycle the channel repeatedly, mirroring every other cycle.
 Default Value
default
 Use the constant value specified in the Default Value parameter.
Default Value defval
 The value used for the Default Value extend condition.
Parameters  Common Page
Time Slice timeslice
 Turning this on forces the channels to be "Time Sliced". A Time Slice is the time between the last cook frame and the current cook frame.
Scope scope
 To determine which channels get affected, some CHOPs use a Scope string on the Common page.
Sample Rate Match srselect
 ⊞  Handle cases where multiple input CHOPs' sample rates are different. When Resampling occurs, the curves are interpolated according to the Interpolation Method Option, or "Linear" if the Interpolate Options are not available.
 Resample At First Input's Rate
first
 Use rate of first input to resample others.
 Resample At Maximum Rate
max
 Resample to the highest sample rate.
 Resample At Minimum Rate
min
 Resample to the lowest sample rate.
 Error If Rates Differ
err
 Doesn't accept conflicting sample rates.
Export Method exportmethod
 ⊞  This will determine how to connect the CHOP channel to the parameter. Refer to the Export article for more information.
 DAT Table by Index
datindex
 Uses the docked DAT table and references the channel via the index of the channel in the CHOP.
 DAT Table by Name
datname
 Uses the docked DAT table and references the channel via the name of the channel in the CHOP.
 Channel Name is Path:Parameter
autoname
 The channel is the full destination of where to export to, such hasgeo1/transform1:tx
.
Export Root autoexportroot
 This path points to the root node where all of the paths that exporting by Channel Name is Path:Parameter are relative to.
Export Table exporttable
 The DAT used to hold the export information when using the DAT Table Export Methods (See above).
Operator Inputs
 Input 0 
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