A system for use in an electronic musical instrument, which system includes a musical sound generating unit for generating a musical sound, and a detection unit for detecting that the magnitude of the musical sound data generated by the musical sound generating unit exceeds a processing capability, on the basis that the value indicated by the most significant bit prior to data processing not equal to that after data processing. A maintaining unit is also included which forcibly maintain the level of a signal representing the musical sound data at a maximum amplitude thereof, on the basis of the result of the detection effected by detection unit.