Perceived Quality Degradation Research Articles

Fast SOLA-Based Time Scale Modification Using Envelope Matching

Time scale modification (TSM) of speech and audio signals is very useful in many applications such as MPEG-4 and fast/slow browsing of pre-recorded materials. Synchronized Overlap-and-Add (SOLA) is a time-domain TSM algorithm known to achieve good speech and audio quality. One problem of SOLA is that it requires a large amount of computation in the search of the best matching point between the analysis and synthesis frames. In this paper, we propose two algorithms, envelope-matching TSM (EM-TSM) and modified EM-TSM (MEM-TSM), to simplify the computation with negligible perceptual quality degradation. In EM-TSM, 1-bit sign information is used in the search to substitute the full-precision signal samples used in SOLA. Three additional computation reduction measures, namely simplified formulation, recursive computation and search-point reduction, are applied to achieve significant computation reduction. In MEM-TSM, we reduce the computation of EM-TSM further by introducing zero-crossing point reduction and predictive search skipping. We also improve the quality of the time-scaled signals by introducing multiple-candidate re-examination, and frame-size modification. Simulation results show that the proposed MEM-TSM can achieve computational reduction factors as large as 300 with very good perceptual quality of time-scaled speech and audio.

Low rate WI SEW representation using a REW-implicit pulse model

Reducing the bit rate of waveform interpolation speech coders while maintaining the perceptual quality has been the focus of a great deal of research. This letter proposes a new method of slowly evolving waveform (SEW) quantization specifically targeted at low rate coding. The proposed method uses a pulse model whose parameters are implicitly contained in the quantized rapidly evolving waveform (REW) parameters, thus requiring no bits for transmission. Results indicate no degradation in perceptual speech quality when compared to that of the existing SEW quantization method. This retention of perceptual quality is in spite of a 12% reduction in the overall coder bit rate.