Multimode Tree Coding of Speech with Perceptual Pre-weighting and Post-weighting

A low delay and low complexity speech coder based on Multimode Tree Coding is proposed. In our Multimode Tree Coder, a simple mode classification method along with frame energy are used to classify the input speech frames into five different modes. Each mode is coded at a suitable bit-rate using a Tree coder with computationally efficient perceptual error pre-weighting and post-weighting filters, and a G.727 Code Generator. At an average bit-rate about 12 kbps for 50% Voice Activity sequences, the variable rate Multimode Tree Coder produces speech quality equivalent to the G.727 ADPCM coder at 32 kbps, resulting in nearly 63% bit-rate saving. Apart from bit-rate savings, a low delay of 6.125 ms, and low complexity are achieved by our Multimode Tree Coder, making it an interesting alternative to the AMR-NB Codec.