Noise

The Noise modifier uses a pseudo-random number generator to variably distribute the property along the stroke.

Amplitude

The maximum value of the noise. A higher amplitude means a less transparent (more solid) stroke.

Period

The period of the noise. This means how quickly the property value can change. A higher value means a more smoothly changing color along the stroke.

Seed

Seed used by the pseudo-random number generator.

Asymmetric

Thickness only -- Allows the thickness to be distributed unevenly at every point. Internally, the stroke is represented as a backbone with a thickness to the right and left side. All other thickness shaders make sure that the left and right thickness values are equal. For the Noise shader however, a meaningful (and good-looking) result can be created by assigning different values to either side of the backbone.

Effect generated with a noise thickness modifier using asymmetric thickness.