From my understanding, the ADC's are still fixed point and linear. Two (or more) then run in parallel over different signal levels to produce the 32-bit float output.
Encoding audio with different log-scale companding has been around for some time too (since the 1970's) with A-law and mu-law in G.711.
Encoding audio with different log-scale companding has been around for some time too (since the 1970's) with A-law and mu-law in G.711.