A composite hearing aid system comprises two hearing aids (11, 31) with respective microphones (12, 32) and electronic receivers (17, 37), a microphone (42) and a transmitter (41) adapted to transmit the signal from the microphone (42) to the electronic receivers. At least one of the hearing aids (11, 31) comprises means for inverting the phase of the signal received by the electronic receivers (17, 37). When the phase of the received signal is inverted in one of the hearing aids (11, 31), a release from masking is obtained, and the perceived signal-to-noise ratio is improved. The invention provides a composite hearing aid system, a hearing aid and a method for processing audio signals.