The present disclosure relates to a signal processing apparatus and system. In calibration, a sensor section is used to acquire a time of day when a stereo camera image capturing a target is acquired and a time of day when a radar image capturing the target is acquired. The target has a radar reflector and a marker. The image acquisition times of day are acquired while at the same time changing a distance between the sensor section and the target so as to find an amount of time-of-day discrepancy, a difference in time of day between the stereo camera image and the radar image at the same distance. At the time of object detection, the radar image acquired first is buffered and then output together with the stereo camera image acquired by the time-of-day discrepancy later, thus combining the stereo camera image and the radar image.