An unified unit-selection framework for

We propose a unified framework for segment quantization of speech at ultra low bit-rates of 150 bits/sec based on unit-selection principle using a modified one-pass dynamic programming algorithm. The algorithm handles both fixedand variablelength units in a unified manner, thereby providing a generalization over two existing unit selection methods, which deal with ‘single-frame’ and ‘segmental’ units differently. The proposed algorithm performs unit-selection based quantization directly on the units of a continuous codebook, thereby not incurring any of the sub optimalities of the existing ‘segmental’ algorithm. Moreover, the existing ‘single-frame’ algorithm becomes a special case of the proposed algorithm. Based on the rate-distortion performance on a multi-speaker database, we show that fixed length units of 6-8 frames perform significantly better than single-frame units and offer similar spectral distortions as variable-length phonetic units, thereby circumventing expensive segmentation and labeling of a continuous database for unit selection based low bit-rate coding.