Finite wordlength effects in quadrature mirror filter banks

The authors investigate the effects of finite wordlength on the performance of QMF (quadrature mirror filter) banks implemented with fixed-point arithmetic. A statistical model for roundoff errors is used to predict the output roundoff noise in each subband. The amplitudes of the parasitic oscillations which are due to a DC component in each subband are predicted with the same model. For two´s complement arithmetic, the authors discuss the effects of truncation and rounding, and present analysis results. A general framework for analyzing different splitting schemes is given. The enhancement of roundoff noise for low frequencies is obvious. It is pointed out that parasitic frequency components can be avoided if two´s complement rounding is used, while roundoff noise can only be reduced by increasing the wordlength