A body of anatomical, electrophysiological, psychophysical, and behavioral research supports the proposition that there is a division in audition similar to the rod/cone dichotomy in vision. Evidence will be presented for the presence of discrete processes for low and high intensity sounds. Both can be identified in electrophysiological measurements at all levels of the auditory nervous system. Both processes can also be discerned in magnitude estimates of loudness. If subjective loudness is plotted as a function of the cube root of sound pressure, the curve consists of two linear sections with a discontinuity of slope at approximately 65 dB SPL. Both segments are present for frequencies up to at least 3 kHz. Linearity is preserved in the presence of a masking noise but the variation in slope and intercept constants suggests the operation of different mechanisms of masking for each process.