Low Delay Modulated Filter Bank

摘要

The document relates to modulated sub-sampled digital filter banks, as well as to methods and systems for the design of such filter banks. In particular, the present document proposes a method and apparatus for the improvement of low delay modulated digital filter banks. The method employs modulation of an asymmetric low-pass prototype filter and a new method for optimizing the coefficients of this filter. Further, a specific design for a 64 channel filter bank using a prototype filter length of 640 coefficients and a system delay of 319 samples is given. The method substantially reduces artifacts due to aliasing emerging from independent modifications of subband signals, for example when using a filter bank as a spectral equalizer. The method is preferably implemented in software, running on a standard PC or a digital signal processor (DSP), but can also be hardcoded on a custom chip. The method offers improvements for various types of digital equalizers, adaptive filters, multiband companders and spectral envelope adjusting filter banks used in high frequency reconstruction (HFR) or parametric stereo systems.

主权项

1. An apparatus for processing an audio signal, the apparatus comprising:
a down sampled low delay decimated analysis filter bank comprising M analysis filters, wherein M is greater than 1 and wherein the M analysis filters are generated based on an asymmetric prototype filter p0(n) having a length N; and a down sampled low delay decimated synthesis filter bank comprising M synthesis filters, wherein the M synthesis filters are generated based on the asymmetric prototype filter p0(n); wherein the M analysis filters and the M synthesis filters are interpolated from the asymmetric prototype filter p0(n) according to:12[p0(2i+1)+p0(2i)],0≤i<320.