Time-varying MMSE modulated lapped transform and its applications to transform coding for speech and audio signals

  • Authors:

  • Guangyu Wang;Ulrich Heute

  • Affiliations:

  • Infineon Technologies AG, D-81541 Munich, Germany;Institute for Circuit and System Theory, University of Kiel, Kaiserstr. 2, D-24143 Kiel, Germany

  • Venue:
  • Signal Processing
  • Year:
  • 2002

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Abstract

The time-varying modulated lapped transform (MLT) is used in speech and audio coding schemes to adjust the time-frequency resolution, to eliminate pre-echoes in the reconstructed signal, and to improve the coding quality. In order to maintain the perfect-reconstruction property in transition periods, an asymmetrical window has to be used at cost of poorer frequency characteristics. We firstly generalize a window-design method for transition periods in the time-varying MLT with a rigorous proof of its PR property, then present a new window-design method, with which the prototype window is so designed that the total reconstruction distortion in presence of coefficient quantization is minimized. This leads to the time-varying minimum mean-square error (MMSE) MLT. Experiments have shown that the designed windows have better frequency characteristics than the sine window in both transition and regular periods. A general formulation of the quantization distortion for different quantization-error models and for all coding systems is given. A simplified optimal window-design algorithm without direct minimization of the distortion equation is suggested. As an example a transform-coding scheme with time-varying MMSE MLT for speech and audio signals is presented.