Generates spatially coherent 3D noise.
turb(X, Y, Z, depth)
Spatially coherent noise gives random numbers which are close to each other when the X, Y, Z inputs are close to each other.
depth is the amount of fractalization done to the noise.
The noise is calculated on a unit-spaced lattice. This means the noise will be independent between points one unit distance apart. You can scale the inputs to achieve different frequencies.
The range is usually within -1 to 1, but can exceed it depending on the depth. The maximum range is -2 to 2 for high depths.