Signal Processing Device, Sonic System and Vehicle

The present disclosure provides a signal processing device. The signal processing device includes: a transmission signal generation unit, configured to generate a transmission signal for a transmitted wave of sound wave; a reception signal output unit, configured to output a received signal based on a received wave of sound wave; and a reflected wave detection unit. The reflected wave detection unit is configured to detect a first reflected wave of the transmitted wave that may be included in the received wave based on a first timing when an envelope detection signal, which is a signal obtained by envelope detection of an absolute value of the received signal during a reverberation period in which a reverberation of the transmitted wave remains, is lower than a first threshold value.