Application of Unimodular Filterbanks for Audio Coding

Abstract

This paper contains the application of Unimodular Filterbanks (UMFBs) based on two new structures for audio coding. Two key properties make UMFBs ideal for audio coding applications. Firstly, they have the lowest possible system delay of M ¿ 1 samples, where M is the number of channels. This property resolves the problem of pre-echoes. Secondly, the presence of nilpotent matrix in the structure furnishes unequal lengths of analysis and synthesis filters to adapt to perceptual limits; long analysis filters for good frequency selectivity and short synthesis filters for noise reduction. The proposed structures ensure perfect reconstruction (PR) and are of minimum delay in the McMillan sense. The number of free parameters is as low as 2M and the optimal set of parameters can be obtained with unconstrained optimization. The low computational overhead makes it suitable for simple and efficient hardware implementation. We have also carried out a brief study of the quantization noise shaping with the proposed structures.