Since the performance of an active sonar is often limited by reverberation, an instrument which could produce accurate reverberation in real time would be valuable to sonar designers, users, and evaluators. An instrument is proposed which can satisfy their needs. It is equivalent to a digital matched-filter processor run backwards, and divides naturally into a hardware portion and a software portion. The complexity of the hardware portion depends only on the transmitter pulse length, receiver bandwidth, and the number of acoustic beams to be produced simultaneously. It employs the fast Fourier transform (FFT) algorithm, for which very fast computer processors. have been developed. The hardware portion of the reverberation generator is developed to the point where it will produce accurate reverberation if provided with the proper input information. The required input information is generated by the software portion of the instrument. It resembles the range-Doppler map produced by a matched-filter processor, except that the smearing caused by the ambiguity function of the pulse must be removed. The software portion is being developed by experimental and theoretical techniques.