Since DVD-ROM data reading speed is faster than its transferring speed to the next data processing block, the data read out is first stored in buffer memory. When the buffer memory overflows, the head jumps to the previous track to re-read the track already read . When monitoring RF signals with DL7440/DL7480, this buffer memory overflow signal is input to the trigger gate terminal, that prohibits triggering during a track-jump period and proceeds with signal analysis, separating unneeded RF signal.