Method and device for detecting a modulation of a physical parameter

The method involves respectively storing first and second sensor signal values (115a,115b) in memories (150,155). The first sensor signal value is recorded with sampling time interval larger than second sensor signal value. Cross-correlation between values is determined to determine decision parameter representing integrated up surface at cross-correlation coefficient at different shift positions using different shift amounts. The modulation of physical quantity is recognized if decision parameter is provided in predetermined relationship with detection threshold. Independent claims are included for the following: (1) the apparatus for detecting modulation of physical quantity; and (2) the computer program product for detecting modulation of physical quantity.