Least-squares design of subsampled allpass transformed DFT filter-banks with LTI property

A new design approach for an allpass transformed analysis-synthesis filter-bank (AS FB) with subsampling is proposed, which can be used for adaptive subband processing with non-uniform time-frequency resolution. Signal reconstruction is performed by an FIR synthesis filter-bank whose coefficients are determined by two different linear least-squares (LS) error designs. The presented unconstrained LS optimization leads to perfect reconstruction (PR), but an insufficient bandpass characteristic for the synthesis subband filters. This problem is solved by a second, equality constrained least-squares (CLS) error design, which achieves near-perfect reconstruction (NPR). In the process, the linear distortions are minimized with the constraint for a linear, time-invariant (LTI) overall transfer function. The aliasing-free reconstruction error is significantly lower than for known designs of allpass transformed DFT filter-banks with NPR. Moreover, the new filter-bank design allows for a low and adjustable signal delay.