A digital audio system of an aircraft comprising one or more pieces of audio equipment and one or more pieces of radio equipment providing a reliable side tone to the operators. The audio equipment and the radio equipment have installed in the proximity, respectively, an audio-terminal and a radio-terminal connected to a digital network including digital messages management units and digital signal processors. The digital messages management unit of the audio equipment is provided with a computer program adapted to generate a side tone of an analog audio message issued by the microphone of the audio equipment and to activate/deactivate its sending to the headset of the audio equipment when the audio-terminal receives from the radio-terminal an activation/deactivation command for said side tone.