New speech enhancement techniques for low bit rate speech coding

In this paper we present novel solutions for pre-processing noisy speech prior to low bit rate speech coding. We strive especially to improve the estimation of spectral parameters and to reduce the additional algorithmic delay caused by the enhancement pre-processor. While the former is achieved using a new adaptive limiting algorithm for the a priori signal-to-noise ratio (SNR) estimate, the latter makes use of a novel overlap/add scheme. Our enhancement techniques were evaluated in conjunction with the 2400 bps mixed excitation linear prediction (MELP) coder by means of formal and informal listening tests.