Abstract: Simulation of sonar reverberation signals is accomplished from square pul the timing and duration of which are computer determined by known principles by processing the pulses through novel shaper means including diode controlled charging and discharging of a capacitor through different selected resistances to provide appropriate ascent and descent curves to the pulses. The shaped pulses are then used to pulse modulate a doppler-shifted carrier signal which is generated by a voltage controlled oscillator responsive to control signals which are functions of ship's speed, transmission angle and the like. The resulting pulse modulated doppler-shifted carrier is then attentuated to provide the desired simulated reverberation signal components.