A method self-adapts signal quality of non-audio data exchanged via an audio channel between a mobile terminal and a payment accessory. The method includes at least one iteration of the following acts: reception, by the mobile terminal, of a reference signal transmitted by the payment accessory; analysis, in the mobile terminal, of the received reference signal, the analysis delivering at least one item of information representative of the quality of the reference signal, referred to as quality information; transmission, by the mobile terminal to the payment accessory, of the quality information. In the above iteration, the roles of the mobile terminal and the payment accessory can be switched.