1. A digital signal processing apparatus for conducting filtering and applying reverberation with respect to a generated musical tone signal, comprising: designating means for generating filtering designation data designating characteristics of said filtering, reverberating designation data designating characteristics of said reverberation, and combination data designating combined characteristics of said filtering and said reverberation, parameter generating means for generating filtering parameters in accordance with said filtering designation data, and for generating reverberating parameters in accordance with said reverberating designation data and said combination data, memory means for storing a plurality of operating algorithms, readout means for reading first and second operating algorithms from said memory means, computing means for filtering said musical tone signal in accordance with said filtering parameters based on said first operating algorithm, and for imparting reverberation characteristics to said musical tone signal in accordance with said reverberating parameters based on said second operating algorithm, said computing means processing said first and said second operating algorithms simultaneously during a single sampling period.