1. A circuit comprising: a signal processing circuit for accepting a discrete-valued input characterizing an observation of a signal and for generating a set of continuous-valued outputs, each output characterizing a corresponding log likelihood ratio (LLR) based measure of an association of the signal with one or more of a set of representative levels, the signal processing circuit including: a plurality of mapping circuits, each configured to map a different range of the discrete-valued input to a respective discrete-valued output signal according to a modeling of the characteristics of the observation of the signal; and a plurality of conversion circuits each configured for accepting the discrete-valued output signal of a corresponding mapping circuit to generate a respective one of the set of continuous-valued output.