Comparison of windowing schemes for speech coding

The majority of speech coding algorithms are based on the code excited linear prediction (CELP) paradigm, modelling the speech signal by linear prediction. This coding approach offers the advantage of a very short algorithmic delay, due to the windowing scheme based on rectangular windowing of the residual of the linear predictor. Although widely used, the performance and structural choices of this windowing scheme have not been extensively documented. In this paper we introduce three alternative windowing schemes, as alternatives to the one already used in CELP codecs. These windowing schemes differ in their handling of transitions between frames. Our subject evaluation shows that omitting the error feedback loop yields an increase in perceptual quality at scenarios with high quantization noise. In addition, objective measures show that while error feedback improves the accuracy slightly at high bitrates, at low bitrates it causes a degradation in quality, resulting in a lower SNR.