1. A digital signal processing apparatus comprising: signal converting means for converting an input analog signal to a multi-valued binary level signal; and a plurality of fundamental elements provided at nodes of a tree structure, each of the fundamental elements performing a first convolution with respect to an input signal and a predetermined scaling function and a second convolution with respect to the input signal and a predetermined wavelet function to wavelet-transform the input signal, wherein the multi-valued binary level signal output from said signal converting means is supplied to the fundamental elements provided at a lowest level of the tree structure, a result of wavelet-transform by fundamental elements at a given level is supplied to fundamental elements at a next higher level, and the scaling function and the wavelet function being determined based on a level of the fundamental elements in the tree structure.