According to an embodiment, a hearing aid system is disclosed. The system includes a speech processor communicatively coupled to a microphone. The speech processor is configured to process a microphone signal received at the speech processor for producing an electrical stimulation signal and an acoustic stimulation signal. The speech processor is also configured to generate a modified acoustic stimulation signal by modifying the acoustic stimulation signal at least for a part of a residual frequency range of a patient in dependence on effect of an implantable electrode array on mechanical properties of cochlea of the patient. The system also includes a first unit and a second unit. The first unit comprising a cochlear implant communicatively coupled to the speech processor, the cochlear implant comprising the implantable electrode array configured to be located within a cochlea of the patient and to provide the electrical stimulation based on the electrical stimulation signal to a cochlea within a non-residual frequency range of the patient. The second unit communicatively coupled to the speech processor and adapted to provide the modified acoustic stimulation based on the modified acoustic stimulation signal to the cochlea within the at least in the part of the residual frequency range.
