This fbm function is a more general fbm that takes more parameters.
basis_type selects from a number of basis noise functions:
0: Perlin basis
1: Ridged basis
2: Voronoi basis
x is a 3-vector at which the noise is evaluated.
H controls the fractal dimension: a larger value causes faster attenuation of higher frequencies.
A good default value is 1.
Lacunarity determines the gap in frequencies between different 'octaves' of noise.
A larger lacunarity means each subsequence octave will have higher frequency.
A good default value is 2.
Octaves determines the number of octaves of noise that are added together. If the value has a fractional component, the last octave is attenuated by the fractional part then added.
Effect of number of octaves
Effect of fractal dimension (H)
Effect of Lacunarity
You can download the example Indigo scene used in the images above here.