Abstract: The aim of this document is to introduce acoustic signal processing in passive sonar system with towed array. The concept of the „acoustic signals processing” includes all possible operations on analogue signals such as amplifying, filtering, sampling and most importantly - operations on digital signals obtained in the sampling process. Digital operations executed in the system include: synchronizing, conversion, sorting, creating deflected beams sets, plotting the power density spectrum received signals and imaging the results. Apart from digital signals processing, we focus on reciprocal connections between microcontrollers and processors in which processing is performed. At the end of this document some exemplary imagings of the output are presented, obtained at the marine testing of this system.