Many comments point to regularities being present in waves. This makes me wonder; for eg sampling problems, it is possible to construct a sampling of a fair coi

Many comments point to regularities being present in waves. This makes me wonder; for eg sampling problems, it is possible to construct a sampling of a fair coin given a biased coin (eg discard HH, TT, take HT and TH to be the flip; I believe many other sampling methods exist). Given a source of low entropy randomness, what is the best way to convert it into a source indistinguishable from true randomness? Would suitably hashing the low entropy source be sufficient, since good hash functions are supposed to possess avalanche effect and be indistinguishable from randomness (perhaps with schemes of eg recursive hash salting to guard against “replays” from the source) (Is this the kind of stuff that goes on in the kernel /dev/random)?