Digital mixer and digital mixing method

To mix signals of a plurality of input channels (45), first buses (46) and second buses (49) are provided. It is possible that, even when a user has selected a desired first surround mode and a desired effect to be imparted, an effecter (9) is capable of performing only an effect process corresponding to a second surround mode. However, if arrangements are made such that the input signals are subjected to level adjustment corresponding to the second surround mode and mixed via the second buses to the effecter, the effecter can impart the mixed signals with an effect corresponding to the second surround mode. The effect-imparted signals are returned to the first buses, and mixed on the first buses to provide effect-imparted signals corresponding to the first surround mode. In the second surround mode, sound image localization may be controlled to follow localization in the first surround mode.