A filterbank for filtering an information signal, the filterbank structure comprising a filter means defining a filter bandwidth, said filter means filtering said information signal and separating said information signal into a plurality of frequency band signals each representing one of a plurality of uniformly spaced frequency bands within said filter bandwidth;
- wherein the filter means comprises:
- (a) a first analysis filterbank means for separating said information signal into a plurality of N separate frequency band signals;
- (b) a processing means for receiving and processing each of said separate frequency band signals to provide N separate processed frequency band signals;
- and
- (c) a second synthesis filterbank means for receiving and recombining the N separate processed frequency band signals into a single output signal;
- wherein the first analysis filterbank means, the processing means and the second synthesis filterbank means utilize digital signal processing, the first analysis filterbank means being adapted to receive an input digital sample stream and the second synthesis filterbank means providing an output digital data stream as the output signal;
- wherein the filterbank circuit includes an analog-to-digital conversion means connected to said first analysis filterbank for receiving said information signal and for converting said information signal into said input digital sample stream at an initial input sampling rate which forms said information signal for the analysis filterbank, and a digital-to-analog conversion means connected to said second synthesis filterbank for converting the output digital data stream to form an analog version of said single output signal;
- and
- wherein the first analysis filterbank means comprises:
- (a) a blocking means for receiving the input digital sample stream and blocking a first number, R where R≦N, of the digital samples so as to provide a blocked input digital sample stream, the ratio of N/R corresponding to an oversampling factor;
- (b) an analysis window means for applying an analysis window function to the input digital sample stream to provide a windowed blocked digital sample stream, said analysis window function being defined by a set of analysis window coefficients;
- (c) a time folding means for overlapping and adding blocks of said windowed blocked digital sample stream, each of said blocks comprising N digital samples, to provide a summed block of N digital samples;
- and
- (d) a discrete transform means for receiving said summed block of N digital samples and transforming the N digital samples into a discrete frequency domain signal having N components, the N components corresponding to the N frequency band signals.