An auditory model “PhyBAM” is presented, which in the long term aims at reproducing the human auditory perception. In recent years, the awareness has grown that many perceptive features have their origin in the peripheral ear, above all in the cochlea. In the present stage, PhyBAM is actually just a model of the peripheral ear. To simulate the perception of arbitrary sound signals, the signal processing occurring in the cochlea has to be formulated close to the physiological basis. Even so the model must be kept as simple as possible for the given aim. As a compromise, PhyBAM is set up as an ordinary circuit model. In this first of two associated papers, the model structure and the computational methods are presented. The model covers ear canal, middle ear, and cochlea. The cochlea model is by far the most sophisticated part. To include the unsymmetrical conditions at both cochlear windows and the resulting common and differential modes, a two-canal circuit is used. The main challenge is the implementation of the cochlear amplifier on the basis of measured tuning curves and otoacoustic emissions. Finding an appropriate model structure and proper parameters turns PhyBAM into an instrument of cochlear research.