yeah just gotta move between 0 and 1 and all is well
Simplex is a little more lenient since you can use the integer scale, but for zooming you still have to deal with the partial movements in the 0-1 scale along whatever zoom area/volume/hyperwhatever you are looking at. You can't just say 'i was at 0-1 and now zooming im at 0-20 or whatever, since that will screw up things a bit. Take whatever scale you begin at (perlin being 0-1 nominally and simplex being whatever to whatever) and scale within that range.
Perlin works as a gradient that is always 0 (parallel to the world) at integers. It looks vaguely like a sin/cos wave function since it is deterministic at integers, but gives more interesting results the more dimensions you use. While Perlin noise uses exponentially larger numbers of gradient points the higher dimension that is observed, Simplex noise is therefore faster the higher dimension you are looking at due to the number of points within the simplex defining how fast it runs.
A 2d Simplex uses d+1 points to define its simplex, so for a 2D grid it uses equilateral triangles to define it. For a 3D volume it uses the 4 point tetrahedron. 4D is difficult to visualize, sadly, but follows the same ruleset of N+1 gradient points instead of Perlin's N^2 points ( I think this is correct, has been a few months since I played with Perlin directly so numbers may be a little off).
Hope this information helps