Methods for compensation of imbalance between I (In-phase) and Q (Quadrature) signal paths (12a, 12b, 605a, 605b) in a quadrature receiver (8) and a quadrature transmitter (600) are disclosed. In the receiver case, the imbalance is compensated for by means of post-distortion in the digital domain. In the transmitter case, the imbalance is compensated for by means of pre-distortion in the digital domain. The methods can be carried out with a relatively low computational complexity. Signal-processing devices (30, 610) for carrying out the methods are disclosed as well. The same basic internal structure may be used for the signal-processing device (30) in the receiver case as for the signal processing device (610) in the transmitter case.