Recently, significant progress has been made in understanding the contribution of the mammalian cochlear outer hair cells (OHCs) to normal auditory signal processing. In the present paper an outer hair cell model is incorporated in a complete, time-domain, one-dimensional cochlear model. The two models control each other through cochlear partition movement and pressure. An OHC gain (gamma) is defined to indicate the outer hair cell contribution at each location along the cochlear partition. Its value ranges from 0 to 1: gamma=0 represents a cochlea with no active OHCs, gamma=1 represents a nonrealistic cochlea that becomes unstable at resonance frequencies, and gamma=0.5 represents an ideal cochlea. The model simulations reveal typical normal and abnormal excitation patterns according to the value of gamma. The model output is used to estimate normal and hearing-impairment audiograms. High frequency loss is predicted by the model, when the OHC gain is relatively small at the basal part of the cochlear partition. The model predicts phonal trauma audiograms, when the OHC gain is random along the cochlear partition. A maximum threshold shift of about 60 dB is obtained at 4 kHz.