1. A signal receiver configured to process two receive phase signals, having a gain control circuit comprising: detection means configured to identify for each phase signal: (a) a first number of samples during a part of a training period for which that phase signal exceeds a first threshold, (b) a second number of samples during a part of the training period for which that phase signal is below minus the first threshold, and to determine for each phase signal a respective minimum value that is equal to a smaller of the first and second numbers of samples; a first gain stimulus generator configured to generate a first gain stimulus in dependence on the two minimum values; averaging means configured to compute an average of the signal received by the receiver during the training period; a second gain stimulus generator configured to generate a second gain stimulus in dependence on the average estimated by the averaging means during the training period; and a gain control signal generator configured to generate a gain control signal for the receiver in dependence on the first gain stimulus and the second gain stimulus.