According to a first aspect, a sound processor unit of a cochlear implant system is disclosed. The sound processor unit comprises an electric circuit, which comprises a sound processor antenna with a sound processor antenna capacitance and a sound processor antenna inductance, wherein the sound processor antenna capacitance and the sound processor antenna inductance are connected in series and form a resonant circuit. An improved cochlear implant system is provided in that the electric circuit of the sound processor unit further comprises a switching element connected in series with the sound processor antenna capacitance and the sound processor antenna inductance, and the electric circuit of the sound processor unit further comprises an inductive element connected in parallel with the switching element, wherein when the switching element is in a closed state, the inductive element is in a short-circuited state and the sound processor antenna has a first resonant frequency, and when the switching element is in an open state, the inductive element is in a non-short-circuited state and the sound processor antenna has a second resonant frequency which differs from the first resonant frequency.