An audio device for modifying the voice transmitted during a telephone call particularly suitable for a mobile telephone system receives from the user of the audio device an analog speech signal. A converter converts the analog speech signal into a digital speech signal comprising at least one fundamental frequency. A set of coded data represents a musical score comprising a set of notes, each note being defined by a fundamental frequency, a duration, and an instrument that plays the note. A digital music signal is extracted from the set of coded data, and a first portion of the digital speech signal is mixed with a first portion of the digital music signal to produce a combined digital signal.