Automatic 1-D de-noising - what is "threshold rescaling using a single estimation of level noise"?

Hello,

The "wden" function for automatic 1-D denoising has an input parameter defining threshold rescaling.

Could anyone please help me understand what the "sln" rescaling option means exactly?

It is said to handle threshold rescaling using a single estimation of level noise based on the first-level coefficients. However, I do not seem to understand how the estimated level gets rescaled at the second and higher wavelet decomposition levels? How is this rescaling option different from "one"?