An audio signal processing method performs signal processing on a first audio signal to be outputted to a first device that a performer uses, the first audio signal on which the signal processing has been performed being a second audio signal, receiving a setting that causes the first audio signal to send to a monitor bus which is for to output the second audio signal, and performing signal processing on the second audio signal, which is received via the monitor bus and is to be outputted to a second device different from the first device, such that a sound quality of a sound to be outputted by the second device is closer to sound quality of a sound to be outputted by the first device than in a case where the signal processing is not performed on the second audio signal.