An aspect of the disclosure is to provide a method and a hearing aid system comprising; a microphone unit configured to receive an acoustical input and provide an audio signal based on the acoustical input, and wherein the audio signal includes a sound pressure level; a storing unit including a normal hearing loudness model, a loudness scheme, a stimulation model and a coding parameter model; a sound output unit configured to stimulate auditory nerve fibers of a recipient of the hearing aid system based on audible stimulations; a processing unit configured to; extract a normal hearing loudness based on the sound pressure level and the normal hearing loudness model, and the normal hearing loudness model includes a plurality of normal hearing loudness as a function of a plurality of sound pressure levels; transform the normal hearing loudness to a secondary hearing loudness according to a loudness scheme; determine a stimulation level within a dynamic range of a recipient of the hearing aid system based on the secondary hearing loudness and the stimulation model, where the stimulation model includes a relation between a plurality of stimulation levels and a plurality of secondary hearing loudness; determine one or more stimulation coding parameters based on the coding parameter model, where the coding parameter model includes a relation between the determined stimulation level and the one or more stimulation coding parameters; and wherein the processing unit is configured to generate the audible stimulations based on the determined one or more stimulation coding parameters and provide the audible stimulations via the sound output unit to the auditory nerve fibers of the recipient of the hearing aid system such that the recipient perceives the secondary hearing loudness.