An 32-kbps ADPCM encoding with a variable initially large leakage and adaptive dual loop predictors

To cope with effects of channel bit errors, a robust quantizer design is proposed. A large leakage is variable initially inserted into the quantizer step size adaptation. In addition, two adaptive predictors in parallel are included in the feed- back loop of an ADPCM encoding system, in which the algorithm of the steepest descent method for predictor coefficient updating is modified to improve robustness. A 32-kbps 4-bit ADPCM encoder with a modified leaky adaptive quantizer and two 2nd order adaptive predictors operating in parallel was evaluated by calculating segmental and long-term averaged signal to distortion ratios. It is shown by computer simulations that this new ADPCM encoding scheme can result in more robust behavior than conventional ADPCM encoding scheme with a first order fixed predictor.