Multirate synthesis of reverberators using subband filtering

As an important element in three-dimensional audio reproduction, reverberators serve to enhance the sense of spaciousness by synthesizing the sound reflections and reverberations pertaining to a particular listening environment. However, direct implementation of room responses generally proves impractical due to the extreme complexity of system dynamics. To overcome the difficulties encountered in long convolutions, an efficient multirate signal processing technique is proposed in this paper on the basis of subband filtering scheme. In this method, the frequency dependent property of reverberation time is incorporated into the design procedure. Further simplification follows from the synthesized infinite impulse response (IIR) implementation for each subband. Specifically, the regular IIR filter, the cascaded comb filters and nested allpass filters, and the cascaded comb filter and an FIR filter are developed to implement the subband filters. Genetic algorithms (GA) are employed to optimize the parameters of reverberators. Subjective listening tests are carried out to assess the performance of the proposed techniques. The results demonstrate that the implemented multirate reverberators are capable of delivering natural sensation of room reverberations, as compared to direct measurement.