This application relates to methods and apparatus for audio signal processing, for example by a codec. An audio signal processing module (301) has at least one input (303, 304) for receiving first and second input signals (Din1, Din2) and an output path for outputting an output audio signal (Vout). The first and second input signals may be supplied by a first audio component (100) and may correspond to the same source audio data. A controller (305) is configured to compare the first and second input signals and to select one of the first or second input signals as the basis for a signal to be supplied to said output path based on the comparison. The controller may determine a measure of similarity (Sim) in content between the first and second input signals.