Noise - CHOP and TOP

Noise Operators (CHOP and TOP)

Noise is the foundation of organic movement, procedural textures, and any generative behavior that needs a coherent random feel. The Noise CHOP and Noise TOP share the same family of noise functions but operate on different sides of the GPU/CPU divide. Pick the one that matches what you’ll do with the result: per-channel signal work goes through the CHOP; per-pixel image work goes through the TOP.

Noise Types

The two ops do not have identical Type lists. Worth knowing both.

Type	Noise CHOP	Noise TOP	Use for
Sparse	✓	✓	“High quality, continuous noise based on Sparse Convolution”
Hermite	✓	✓	“Quicker than Sparse, but produces lower quality noise”
Harmonic Summation	✓	✓	Sum of progressively higher-frequency harmonics
Brownian	✓	✓	Brownian motion noise (CHOP-listed type)
Random	✓	✓	“(White Noise) Every sample is random and unrelated”
Alligator	✓	✓	“Cell Noise” (Voronoi-style)
Perlin 2D / 3D / 4D		✓ GPU	Classic gradient noise on the GPU (TOP-only)
Simplex 2D / 3D / 4D		✓ GPU	Simplex variant, faster than Perlin in higher dimensions
Random (GPU)		✓ GPU	GPU-side white noise

GPU types are TOP-only and run on the graphics card. Everything else runs on the CPU in both ops.

Shared Key Parameters

Parameter	What it does
Type	Algorithm (see table above)
Period	”The approximate separation between peaks of a noise cycle. It is expressed in Units.” Bigger = wider features
Harmonics	”The number of higher frequency components to layer on top of the base frequency.” More = more detail
Harmonic Spread	”The factor by which the frequency of the harmonics are increased. It is normally 2”
Amplitude	”Defines the noise value’s amplitude (a scale on the values output)“
Offset	DC offset added after amplitude
Seed	”Any number, integer or non-integer, which starts the random number generator”

Animating Noise

Both ops sample noise along a position in noise space. Animate by walking that position over time on the Transform page.

The Noise CHOP wiki explains the technique: “translating, rotating and scaling the line along which the Noise CHOPs samples the noise space” is like “walking in a straight path in the mountains, recording your altitude along the way, then re-starting from the same initial location, walking in a slightly different direction.”

Transform page → tz parameter → expression: absTime.seconds * 0.1

The multiplier sets the speed. 0.1 is slow rolling; 2.0 is jittery.

Noise CHOP Specifics

• Channel Names: takes a pattern. chan[1-3] produces three channels chan1, chan2, chan3, each a separate noise stream.
• Per-sample evaluation: the CHOP evaluates noise at each sample position along the timeline, so a 1-second 60 fps CHOP gives 60 unique noise values.
• Output is unbounded; with default Amplitude the typical range is roughly -0.5 to 0.5. Pipe through a Math CHOP if you need a clean 0..1 or -1..1.

Noise TOP Specifics

• Resolution: set on the Common page. Same as any TOP.
• Monochrome toggle: switches between single-channel grayscale output and 3-channel color noise.
• Output Aspect: maintain input aspect, use resolution-based aspect, or custom.
• Pixel Format: 8-bit fixed clamps the output to [0, 1]; switch to 16- or 32-bit float when you need negative values or HDR (e.g. for displacement maps or normal maps).

Common Patterns

• Drive Geo COMP rotation. Noise CHOP with one channel, exported into geo1.par.Rry, gives organic wobble.
• Procedural displacement map. Noise TOP with Type Perlin 3D, fed as the Normal Map of a PBR MAT, creates a bumpy surface.
• Animated alpha mask. Noise TOP with Monochrome on, fed as an alpha mask in a Composite TOP.
• Spawn jitter for instances. Noise CHOP with three channels, exported as tx ty tz for an instanced Geo COMP.

Common Gotchas

• Period semantics are inverted from frequency. Small Period = high frequency = jittery. Big Period = low frequency = slow rolls. Easy to get backward when reaching for a familiar “frequency” knob.
• Seed jumps reset animation. Changing Seed mid-animation causes a discontinuity. Pick the seed first, then animate.
• Random has no spatial coherence. Two adjacent samples can be wildly different. For smooth movement, never use Random; use Sparse or Perlin.
• GPU and CPU types differ. A patch you build with Noise TOP set to Perlin 2D won’t render the same if you swap the Type to Sparse, even at the same Period. They’re different algorithms.
• Amplitude isn’t a [-1, 1] slider. It’s a multiplier on whatever the underlying noise function returns; that range varies by Type.

Related Nodes

• Constant CHOP: combine with Noise via Math CHOP to bias the output
• LFO CHOP: deterministic oscillation; the regular cousin of Noise
• Math CHOP: remap noise output to whatever range you actually need
• Instancing: feed Noise into per-instance position/color

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