Various embodiments include systems and methods to provide selectable variable gain to signals in measurements using incident radiation. The selectable variable gain may be used to normalize signals modulated in measurements using incident radiation. The selectable variable gain may be attained using a number of different techniques or various combinations of these techniques. These techniques may include modulating a modulator having modulating elements in which at least one modulating element acts on incident radiation differently from another modulating element of the modulator, modulating the use of electronic components in electronic circuitry of a detector, modulating a source of radiation or combinations thereof. Additional apparatus, systems, and methods are disclosed.