A robust variable-rate speech coder

The goal of this study is to develop a robust and high-quality speech coder for wireless communication. The proposed coder is a perceptually-based variable-rate subband coder. The perceptual metric ensures that encoding is optimized to the human listener and is based on calculating the signal-to-mask ratio in short-time frames of the input signal. An adaptive bit allocation scheme is employed and the subband energies are then quantized using a Max-Lloyd quantizer. The coder is fully scalable-increasing the bit rates, improves the quality of encoded speech. Subjective listening tests, using quiet and noisy input signals, indicate that the proposed coder produces high-quality speech when operating at 12 kbps or higher. In error-free conditions, our coder has comparable performance to that of QCELP or GSM coders. For speech in background noise, however, our coder, at 12 kbps, outperforms QCELP significantly, and for music, it outperforms both QCELP and GSM.