1. A method for enhancing an audio signal in relation to a hearing impairment, comprising: obtaining an input signal comprising input sub-band signals in a frequency range comprising a source range and a target range; selectively transposing the input sub-band signals in the source range into transposed sub-band signals in the target range according to a predefined transposing rule; determining a masking threshold based on a predefined perceptual model; detecting perceptually relevant sub-band signals of the transposed sub-band signals in the target range, the perceptually relevant sub-band signals of the transposed sub-band signals in the target range exceeding the masking threshold; and selectively replacing input sub-band signals in the target range with corresponding detected perceptually relevant sub-band signals of the transposed sub-band signals in the target range.